Is it as worm? Is it a caterpillar? NO! It is an onychophoran

A group of small curious caterpillar-like predators hide among forest litter and soil of rainforests and other moist habitats: the onychophorans. Despite few onychophorans species are known worldwide, their anatomical, reproductive and ecological traits make them a unique and independent group of animals. Would you like to know more about them? Keep reading.

Onychophorans or velvet worms are a phylum of small invertebrates that range from 5mm and 15cm, with soft, long and almost non-modified bodies and small conical unjointed legs like those of caterpillars.

Peripatoides novaezealandiae, an onychophoran species from New Zealand. Photo by Gil Wizen (c) (link).

The scientific name of the group, Onychophora, is formed by the Ancient Greek terms onykhos, “claws” and phorós, “to carry“, since on each foot they have a pair of retractable, hardened (sclerotised) chitin claws.

Claws of the onychophoran Euperipatoides kanangrensis. Photo by Martin Smith CC 4.0 (link).

Currently, about 200 species of onychophorans are known worldwide, all of them terrestrial, distributed exclusively in the Southern Hemisphere. They are classified within two families with a mutually exclusive distribution: Peripatidae, with a circumtropical distribution (mainly found in Mexico, Central America, north of South America and Southeastern Asia), and Peripatopsidae, with a circumaustral distribution (mainly Australasia, South Africa and Chile).

Worldwide distribtion of onychophorans. In green: Peripatidae family; in red, Peripatopsidae family; black dots, fossil records. Photo by Benutzer:Achim Raschka CC 3.0 (link).

Some fossil records that date from the early Cambrian suggest that ancient onychophorans probably appeared barely after the Cambrian Explosion and that they eventually moved from water to land.

Who do onychophorans look like?

To date, the most widely accepted idea from both an anatomical and a morphological point of view is that they constitute an independent phylum within Ecdisozoa, i. e., organisms that undergo consecutive molts or ecdysis to change their cuticle, closely related to tardigrades or water bears and arthropods (insects, arachnids and their related groups, myriapods, crustaceans and the extinct trilobites).

Phylogeny of Bilateria (organisms with bilateral symmetry). Source: tolweb.org

Onychophorans, arthropods and tardigrades all together constitute the Panarthropoda group, a monophyletic taxon, i. e., that groups all the descendants of a common ancestor, which validity has been proved by most of studies.

Phylogeny of Panarthropoda. Source: Wikipedia

So, despite resembling worms (annelids), slugs (gastropod mollusks) or caterpillars (lepidopteran larvae), onychophorans do not belong to any of these groups.

Anatomy

Onychophorans have long bodies covered with a thin, flexible chitinous cuticle with pseudo-segmented markings or weak ringed marks. Its cuticle is also covered in tubercles or papillae with sensilla, i. e., small and thin hairs, which give these animals a velvety appearance that gives rise to their common name.

Can you see the papillae that cover its body and the pseudo-segmentation of its cuticle? Photo of the species Eoperipatus totoro by Melvyn Yeo (c) (link)

Their bodies are internally divided into true segments each with a pair of soft, conical, unjointed legs or lobopods, in contrast to those of arthropods. Their movement is from front to back, in a wave, and each pair of legs move in the same direction, so that their way of walking is slow and gradual, making them almost invisible to prey.

The head houses a pair of mandibles, a pair of tiny eyes with chitinous lenses and a developed retinal layer, and a pair of fleshy sensorial appendices resembling antennae of arthropods, but with which they do not share an evolutionary or embryonic origin. They also have a pair of oral papillae near the mouth, each connected to a slime gland that produces and whitish sticky substance or slime they use to hunt or as a defense. These glands occupy almost the entire length of their bodies.

Onicophoran shooting slime through its oral papillae. Photo by Ivo. S. Oliveria and Alexander Baer (c) (link).

Ecology and behaviour

Most of species live primarily in moist, dark microhabitats, such as forest litter and soil, of rainforests or other types of very rainy forests. They are solitary, nocturnal and photonegative, i. e., they hide from light. A very few species are cave dwellings or live in drier woodlands.

All onychophorans are active predators. They hunt pray by shooting an adhesive substance or slime through their oral papillae to immobilize them. They can shoot this substance up to 30 cm:

The slime is 90% water, while its dry residue consists mainly of proteins, sugars, lipids and the surfactant nonylphenol. Onychophorans are the only known organisms able to synthetize the latter substance, which has been widely produced and used by humans for manufacturing, for example, lubricating oils and detergents.

Reproduction

Mating and fertilization

All onychophorans, except the parthenogenetic species Epiperipatus imthurni, reproduce sexually. Females and males show a moderate degree of sexual dimorphism, with females being somewhat larger than males and, in species with a variable number of legs, females have more legs than males.

Fertilization is always internal, even though the way females receive the sperm from males is quite variable. In most onychophorans, males transfer a spermatophore, i. e., a package of sperma, directly to the female’s genital opening. Males of a few species within Paraperipatus genus use a true penis to complete this transference.

However, the strangest case is that of two species within Peripatopsis genus. Males place very small spermatophores on the back or sides of the female; then, amoebocytes from the female’s blood collect on the inside of the deposition side to secrete enzymes that decompose both the spermatophore’s casing and the body wall of the female on which it rests. This releases the sperm, which travels through the female’s blood or haemocoel to reach the ovaries, where fertilization takes place.

Types of reproduction

Onychophorans may be oviparous, ovoviviparous or viviparous.

The most common are the ovoviviparous forms, i.e., very well-developed eggs provided with yolk are retained inside the female’s body and they hatch barely before she gives birth. These forms are exclusively found within the Peripatopsidae family.

Oviparous forms, which are less common, have been observed in organisms inhabiting habitats with non-stable food sources and instable environmental conditions where the egg shell and other eggs structures would act as a protective barrier. As it happens with the ovoviviparous forms, the oviparous are exclusively found within the Peripatopsidae family.

Ooperipatellus species from Australia and New Zealand, Peripatopsidae family. Photo by Simon Grove (c) (link).

On the contrary, viviparous forms are very well-represented in tropical regions with stable environments and food sources both in Peripatopsidae and Peripatidae (the latter with a circumtropical distribution). Females produce very small eggs that are retained inside her uterus and nourished directly by maternal fluids or specialized tissues from the mother’s body (placenta). Several weeks or months later, females give birth to well-developed offspring.

Picture of the first known specimen of Eoperipatus totoro, Peripatidae family, from Vietnam. Its specific name, ‘totoro’, refers to the animated film ‘My neightbor Totoro’ by Hayao Miyazaki (Studio Ghibli), because the onychophoran resembles the catbus that appears in the film (go to the article).

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Main photo by Melvyn Yeo (c)

What’s causing the massive death of the nobel pen shell?

The nobel pen shells are the most emblematic molluscs of the Mediterranean since they only live in this sea. Its drastic reduction due to a parasite has led scientists to declare it as endangered. Do not miss this post to know more about the nobel pen shell and what is leading them to extinction, as well as what is being done and what you can do to save the species! 

THE NOBEL PEN SHELL, THE AFFECTED

The nobel pen shells (Pinna nobilis) are molluscs of the bivalve class. This means that they have a shell formed by two lateral shells, which are joined by a hinge.

The shell of the pen shells is shaped like an ear, hence its scientific name (Pinna), since it has a rounded upper part and the lower one ends in a tip. It is by the lower tip that they are buried in the substrate to hold onto the seabed. It can reach a meter long.

The nobel pen shell (Pinna nobilis) is ear-shaped, hence its scientific name (Picture: Doruk Aygün, Creative Commons).

The nobel pen shells are the most characteristic mollusc of the Mediterranean, since it is in this sea the only place in the world where they live. It is, then, a species endemic to the Mediterranean. They are usually found associated with Posidonia meadows and their presence serves as an indicator of good water quality.

Among its threats are the capture by divers, pollution and anchoring of vessels in the Posidonia meadows. Now, anyway, we must add a new threat: a protozoan, which has led it to be in danger of extinction.

A PROTOZOAN, THE CULPRIT

A parasite that affects the digestive system of the pen shells is the culprit that they are in danger of extinction. Specifically, it is a protozoan of the genus Haplosporidium, which penetrates the digestive gland. How the pathogen has entered the mollusc is still a mystery.

In any case, it must be a very specific pathogen, since it has not affected its “sister” species, Pinna rudis, which lives in the same areas.

NOWADAYS SITUATION

At the beginning of autumn 2016, a massive death of pen shells of the species Pinna nobilis was detected in several points of the Spanish Mediterranean coast.

A study carried out by the Balearic Oceanographic Center of the Spanish Institute of Oceanography has concluded that in most of the Spanish Mediterranean coast there are high mortality rates, up to 100% in some points, especially in the populations of Andalusia, Murcia, Valencia Community and Balearic Islands. In fact, this is the massive mortality event that has most affected the species to date.

Map about the situation of Pinna nobilis in different places of the Western Mediterranean coast (Source: Vázquez-Luis et al. 2017).

In this video, you can see a massive death case in Tangó de Xàbia (Valencia Community):

Fortunately, the populations of the Catalan coast still persist, especially those located in Cap de Creus and in the Ebre Delta.

In addition, the high propagation rate of the protozoan could lead to an even worse situation. It is for this reason that it has been declared as a critically endangered species.

HOW ARE SCIENTISTS SAVING THE NOBEL PEN SHELL?

A project of the Ministry of Agriculture and Fisheries, Food and Environment of the Government of Spain, with a cost of 491,521 euros, aims to rescue 215 specimens of the species.

The project consists in its extraction, rescue and conservation in different centres, with the final goal of keeping the specimens healthy to avoid their infection, maintain the species, have a genetic reserve and, in the future, repopulate their habitats again and try reproduce the species in captivity.

WHAT CAN I DO?

According to a decalogue from the Spanish Malacology Society, this is what has to be done in case of finding a nobel pen shell.

In case the animal is alive: 

1. Do not disturb, damage or tear the animal.
2. Do not touch the animal under any circumstances, since the protozoan generates many spores and could contaminate it.
3. Do not disturb the animal by putting us on it, lighting it with a flashlight or trying to open its shells.
4. Try to identify the Pinna species. The young specimens of P. nobilis and P. rudis can be distinguished by the number and size of the ribs of the shells: in P. nobilis they are much smaller and numerous. In larger specimens it is more complicated.
5. If the animal is covered with organisms, even if they are of invasive exotic species, the animal should be left untouched and untapped.
6. If the mollusk is alive but lying on the bottom, do not touch so as not to damage it or infect it.
7. If we see that there are divers or other people touching or bothering an animal, we should gently remove it from the animal.
8. If we see that a diver or fisherman has captured a live animal and tries to get it out of the water or has done so, we must return it to the sea as soon as possible and call the 112 telephone so that the competent authorities take the appropriate measures.

Pinna rudis can be distinguished from Pinna nobilis by the presence of bigger and less numerous ribs (Picture: Creative Commons)

In case the animal is death: 

1. If we find an empty shell, we should leave it in the water. It is a protected species.
2. If we find a dead pen shell with remains of the organism, we should not touch it or move it so as not to expand the pathogen.

Other complementary measures: 

1. If we are going to dive with a boat or sail, in no case will we drop the anchor if there is Posidonia in the seabed.
2. If we have dived in areas with death pen shells, we must clean the equipment with diluted bleach or detergent to prevent the spread of the pathogen to other areas.
3. If you see a live or recently dead specimen of Pinna nobilis, tell it to bzn-biomarina@mapama.es and to cob@ba.ieo.es with the subject “Nacra”.

REFERENCES

• Decálogo de Buenas Prácticas con Pinna nobilis (Sociedad Española de Malacología).
• Maite Vázquez-Luis, Elvira Álvarez, Agustín Barrajón, José R. García-March, Amalia Grau, Iris E. Hendriks, Santiago Jiménez, Diego Kersting, Diego Moreno, Marta Pérez, Juan M. Ruiz, Jordi Sánchez, Antonio Villalba and Salud Deudero, 2017. S.O.S. Pinna nobilis: A Mass Mortality Event in Western Mediterranean Sea. Front. Mar. Sci., 17 July 2017. https://doi.org/10.3389/fmars.2017.00220
• Cover picture: unknown author.

Opisthobranchs: what are they and Mediterranean species

The opisthobranchs are one of the marine animal groups that most attract the attention of divers and lovers of underwater life. Do you want to discover what are they, some curiosities and some species of the Mediterranean?

Most photographs are courtesy of the biologist and oceanographer Marc Collell. Visit his Instagram (@mcollell) and enjoy!

THE GASTROPODA MOLLUSCS

The opisthobranchs are a group of marine animals included in the gastropod molluscs, along with snails, limpets, slugs and periwinkles, among others.

Snails and opisthobranchs are included in the same group of molluscs (Picture: Jürgen Schoner, Creative Commons).

The gastropods, which constitute the largest group of molluscs, with about 70,000 living species and 15,000 fossils, are characterised by a torsion process, a process that takes place in the veliger larva stage, whereby the visceral organs rotate up to 180º. As a result of this process, the anus and mantle cavity are located on the anterior side and are opened above the mouth and head.

However, some groups have reversed the process, so that the anus opens on the right or posterior side.

The gastropods have traditionally been classified into three subclasses:

• Prosobranchia: include most marine snails and some freshwater and terrestrial gastropods. Upon suffering the torsion process, the mantle cavity is anterior and the gill or gills are placed in front of the heart.
• Opisthobranchs: it is the group that occupies us.
• Pulmonata: include land snails, freshwater snails and slugs. Instead of gills, they have lungs.

WHAT ARE OPISTHOBRANCHS?

The opisthobranchs include marine slugs, sea hares and marine butterflies, among others. They are popularly known as nudibranchs, but in reality nudibranchs are only a group of opisthobranchs.

The opisthobranchs have totally or partially reversed the torsion process, so that the anus and gill (if any) are on the right or posterior side. They have two pairs of tentacles, and the second is often modified and named rhinophore, so that it presents a set of folds that increases the chemioreceptor surface and that has an appearance of ears. They have shell or not.

Opisthobranchs have suffered a total or partial process of reversed torsion, so they look as if they had a symmetric body (Picture courtesy of Marc Collell, @mcollell).

The opisthobranchs, at the same time, can be divided into 11 suborders, to emphasise: the nudibranchs, the Sacoglossa and the Anaspidea.

• Nudibranchs have bare gills and never have shells. Gills may have different morphologies and can be located in different parts of the body. They are carnivorous and feed on other invertebrates and nudibranch eggs.
• The Sacoglossa have much more distinct forms and may have shell or not. They normally feed on body fluids from seaweed.
• Anaspidea are popularly called sea hares. They are characterised by having two large lateral expansions in the foot called parapodiums. In addition, they have a very thin inner dorsal shell. Its popular name is due to the fact that rhinophores develop so much that they look like ears.

THE COLOUR OF OPISTHOBRANCHS

If something characterises the opisthobranchia is its variety of colouration, some with very colourful and alarming colours (aposematic coloration) and others with more discrete colouration that are disguised with the substrate (cryptic).

Facelina annulicornis is a nudibranch with cryptic colouration (Picture courtesy of Marc Collell, @mcollell)).

SOME CURIOSITIES OF OPISTHOBRANCHS

Some nudibranchs have the ability to incorporate the urticating cells they ingest from anemones and hydrozoa, such as the plumose marine algae (Aeolid). These have elongated papillae on the back, called cerata, in which the nematocytes of the cnidarians, which serve as a defense, accumulate.

Hermissenda crassicornis is a nudibranch with cerata (Picture: Magnus Manske, Creative Commons).

There are photosynthetic sacoglossal opisthobranchs. This is the case of Elysia chlorotica. This mollusc from North America has the capacity to perform photosynthesis because it incorporates the chloroplasts of the algae it consumes.

Elysia chlorotica has the ability to perform photosynthesis (Picture: Karen N. Pelletreau et al., Creative Commons)

9 EXAMPLES OF MEDITERRANEAN OPISTHOBRANCHS

Aplysia depilans 

Aplysia depilans (Picture courtesy of Marc Collell, @mcollell).

Aplysia depilans is an opisthobranch of the Anaspidea group that is distributed by all the Mediterranean. This sea hare, which is one of the largest in European waters, can reach 30 cm and weigh 1 kg. Its coloration may be brown or greenish, with white or yellowish spots. It lives in shallow seafloor of the coast, where there are abundant algae, from which it feeds.

Cyerce cristallina

Cyerce cristallina (Picture courtesy of Marc Collell, @mcollell).

Cyerce cristallina is an opisthobranch of the Sacoglossa group that is distributed throughout the Mediterranean, in addition to the Atlantic. It has a maximum length of 3.5 cm. Its cream-coloured body may be white, brown or reddish. It is a herbivorous species, which feeds on algae. It has the ability to release the cerata if it feels threatened, which continue to move to distract the opponent.

Placida verticilata

Placida verticilata (Picture courtesy of Marc Collell, @mcollell).

Placida verticilata is an opisthobranch of the Sacoglossa group mentioned in the coasts of English Channel, Canary Islands, Azores, Madeira, the Caribbean and the Iberian Peninsula. It measures between 0.7 and 1 cm in length. It has the body full of chloroplasts, which gives it an olive-green colour, with which it does the photosynthesis. It lives on top of the Codium seaweed, from which it feeds.

Peltodoris atromaculata

Peltodoris atromaculata (Picture: Anders Finn Jørgensen, Creative Commons)

Peltodoris atromaculata is a nudibranch, being one of the most abundant species of the Mediterranean, although it also lives in other zones. Its colour recalls a cow. It can measure up to 12 cm in length. It usually lives on rocky bottoms with low lighting, at the entrance of caves and in coralline backgrounds. It feeds on the sponge Petrosia fisciformis.

Dondice banylensis

Dondice banyulensis (Picture courtesy of Marc Collell, @mcollell).

Dondice banylensis is a nudibranch of the Mediterranean, although it has recently been observed in the Atlantic zone of the Strait of Gibraltar. This nudibranch, which can reach 7 cm in length, lives on a wide variety of substrates and habitats. When it feels threatened, it extends its cerata to the sides to defend itself.

Doto floridicola

Doto floridicola (Picture courtesy of Marc Collell, @mcollell).

Doto floridicola is a nudibranch of southern Europe, although it has been observed in the British coasts and Ireland recently. With translucent body, can exceed a centimetre in length. It usually lives with colonies of hydrozoans such as Aglaophenia and Synthecium. The lays are shaped like a ribbon and placed on top of the hydrozoans.

Felimare picta

Felimare picta (Picture courtesy of Marc Collell, @mcollell).

Felimare picta is a nudibranch that, in addition to other areas, lives on the entire coast of the Iberian Peninsula, both Mediterranean and Atlantic. With a length that can exceed 12 cm, even 20 cm  in some specimens, this nudibranch lives on rocky walls with abundant algae, sponges and other invertebrates, especially dimly lit.

Polycera quadrilineata

Polycera qudrilineata (Picture courtesy of Marc Collell, @mcollell).

Polycera quadrilineata is a nudibranch that inhabits the waters between the Atlantic coasts of northern Europe to the Mediterranean. In the Mediterranean they measure about 2 cm, although outside of it they can reach 4 cm. It lives in walls of rocks with little illumination and abundant briozoa, of which it feeds.

Flabellina afinis

Flabellina affinis (Picture courtesy of Marc Collell, @mcollell).

Flabellina afinis is a very abundant nudibranch in all waters of Europe. It can measure up to 5 cm in length. This colourful nudibranch lives normally above the colonies of hydrozoans of the genus Eudendrium, from which it feeds. The laying, with the shape of an undulating cord, is laid on top of the hydrozoans.

If you have not had enough, watch this video:

Now it is high time you take your snorkel gear or dive and dare to look for opisthobranchs. Of course, you must have patience… What other species, besides those mentioned here, have you seen?

REFERENCES

• Club d’Immersió Biologia (CIB)
• Grup de Recerca d’Opistobranquis de Catalunya (GROC)
• Julie A. Schwartz, Nicholas E. Curtis, and Sidney K. Pierce, “FISH Labeling Reveals a Horizontally Transferred Algal (Vaucheria litorea) Nuclear Gene on a Sea Slug (Elysia chlorotica) Chromosome,” The Biological Bulletin 227, no. 3 (December 2014): 300-312. https://doi.org/10.1086/BBLv227n3p300
• Opistobranquios: los arlequines del mar
• OPK – Opistobranquis
• Cover picture: Photo courtesy of Marc Collell (Instagram: @mcollell)

The elderly organisms of the oceans

Have you ever wondered which are the longest-lived organisms of the seas and oceans of the Earth? The sea turtles are well known to have long lives. But, ¿which is the oldest organism of the ocean (and the planet)?

BOWHEAD WHALES

The bowhead whales (Balaena mysticetus), also called Arctic right whales, live most of the year associated with sea ice in the Arctic ocean. These marine mammals are among the largest animals on Earth, weighing up to 75-100 tons and with a length of 14-17 m on males and 16-18 m on females.

Bowhead whale (Balaena mysticetus) (Picture: WWF).

More than 20 years ago, in 1993, it was discovered by chance that bowhead whales have a longer life than previously thought. Their lifespan was considered to be about 50 years, but the unexpected discovery let to know that they live more than 100 years. In fact, some individuals are known to have lived for about 200 years.

Which was that fortuitous discovery? An Alaskan Eskimo hunted an individual with the tip of a harpoon inside its blubber. This harpoon was created with a technique not used for 100 years.

They are among the mammals that get much older, even among other whales. And the explanation to this fact lies on the extreme cold of their habitat: they have to invest so much energy in maintaining the body temperature that their first pregnancy is usually at 26 years and, therefore, they have a long life expectancy.

SEA TURTLES

In the famous Disney movie Finding Nemo, Marlin, Nemo’s father, meets Crush, a 150-year-old sea turtle. However, do sea turtles live so much?

Do you want to discover the amazing life of the sea turtles? Do you want to know the reason why sea turtles are threatened?

Sea turtles have long lives, but their age is unknown (Picture: Key West Aquarium).

It is well-known that sea turtles have a long life, but their ages are barely known. It has been confirmed that growth lines in some turtle bones are laid down annually, but due to growing at different rates depending on the age, this cannot be used to estimate their age.

However, scientist believe that these awesome reptiles may live long like whales. Those turtles that outlive the first stages of life can expect to live at least 50 years. In addition, biological aging is nearly suspended for these animals.

Despite unknowing the age of the oldest wild sea turtle, it is said to be a 400-year-old captive sea turtle in China.

THE OLDEST KNOWN ANIMALS

Black corals are the oldest known animals on Earth. Notwithstanding, they are not the oldest organisms on the planet.

Leiopathes sp. is a genus of black corals that can live several millenniums (Picture: CBS News).

These coal-dark-skeleton corals grow a great deal less than a millimetre per year, such as the Mediterranean red coral. Despite its name, they usually show yellow, red, brown and green colours. Although they are considered deep-sea corals, they are found worldwide and at all depths.

Research in 2009 demonstrated that a Hawaiian black coral individual included in the Leiopathes glaberrima species had been living and growing since the building of Egyptian pyramids; 4,600 years ago.

Like sea turtles, in case an individual survives the first century of age, there is every likelihood of  living for a millennium or more.

THE IMMORTAL JELLYFISH

It is a fact of life that all living beings die; except for Turritopsis nutricula, the immortal jellyfish. This small (4.5 mm) bell-shaped jellyfish is immortal owing to the fact that possess the capability to age in reverse.

The immortal jellyfish, Turritopsis nutricula (Picture: Bored Panda).

This species starts its life being a mass of polyps growing in the seafloor, which in some point produce jellyfishes that develop gonads to create the following generation of polyps, and then die. This has nothing special in comparison with other jellyfishes. Learn more about these beautiful animals here.

This cnidarian species, under the presence of a stressor or injury, transforms all its cells into larval forms. It is that changes from an adult to a larva. Then, every single larva can transform into a new adult. That process is named transdifferentiation. Little do scientists know about this process in the wild.

Transdifferentiation in Turritopsis nutricula (Picture: Bored Panda).

THE OLDEST ORGANISM ON EARTH

The oldest organism on Earth is neither an animal, algae nor a microorganism. The most elderly organism in the planet is a plant. In concrete, a marine plant known as Posidonia oceanica, commonly known as Neptune Grass or Mediterranean tapeweed. Do you want to know the reason why the Posidonia ecosystems are considered the marine jungles?

Posidonia oceanica meadow (Picture: SINC).

Spanish researchers found out that in Formentera (Balearic Islands) there is a 100,000-year-old Posidonia clone. This means this is the longest-living organism on the biosphere.

The key to understand its age is the clonal growth: it is based on the constant division of cells placed in the meristems and on the extremely slow growth of its stalk (rhizomes).

REFERENCES

• Arnaud-Haond S, Duarte CM, Diaz-Almela E, Marba` N, Sintes T, et al. (2012) Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica. PLoS ONE 7(2): e30454. doi:10.1371/journal.pone.0030454
• NOAA: Black corals of Hawaii
• Palumbi, S.R & Palumbi, A.R (2014). The extreme life of the sea. Princepton University Press
• Reference: The oldest sea turtle
• Rugh, D.J. & Shelden, K.E.W. (2009). Bowhead whale. Balaena mysticetus. In Perrin, W.F; Würsig, B & Thewissen, J.G.M. Encyclopedia of Marine Mammals. Academic Press (2 ed).
• Schiffman, J & Breen, M (2008). Comparative oncology: what dogs and other species can teach us about humans with cancer. The Royal Society Publishing. DOI: 10.1098/rstb.2014.0231
• WWF: How long do sea turtles live? And other sea turtle facts
• Cover picture: Takashi Murai (Bored Panda)

Sex change is also in animals

Sex change is not only present in humans (known as transexuality), but there are some examples of animals that change sex, that is, they are born male or female, and throughout his life, species change to the opposite sex. Do you want to know some of these species? Remember that you can also read a post in this blog about Homosexuality in animals.

TRANSEXUALITY IN ANIMALS

The animal sex change is a fact not very widespread, but is present especially among fish and some mollusks, jellyfishes, crustaceans, echinoderms and worms.

However, in the case of animals, the term used is not transsexuality. The change of sex in the animal kingdom is a particular type of hermaphroditism: sequential hermaphroditism.

This change of sex is usually genetically programmed and  it is influenced by the environment in which it develops. However, at birth they have already both sexes, so that sex determination is not given by the genes.

There are different types of sequential hermaphroditism:

• Protandry: when an organisms is born male and changes to female, such as the clownfish (Amphip
• Protogyny: when an organisms is born female and changes to male, such as wrasses.
• Bidirectional sex change: when an organism has both full female and male sexual organs, but act as a male or female during different stages of its life, such as the  fish Lythrypnus dalli. 

It is clear that this strategy supposes an important benefit in front of other species: in front of extreme conditions, the organisms have the capacity of assuring the future generations by changing their sex.

THE CLOWNFISH

The clownfish is one of the best known examples of sex change in the animal kingdom. Our friend Nemo, throughout its life will become a female. Clownfishes are all born males, but after a certain age they change sex. They can also change sex in case the female dies, so although Nemo’s mother died, found his mother in his father.

Couple of clownfishes, with the female bigger than the male (Picture: Georggete Douwma, Arkive).

The form of reproduction of these very colourful and known fishes is most curious: in each anemone, cnidarian animals with which they live in symbiosis, lives a harem, consisting of one female (bigger in size than the male), a reproductive male and several non-breeding males.

Cycle of clownfish changing sex (Picture: The fisheries blog).

Si la hembra muere, el macho reproductor se transforma en hembra y el macho no reproductor de mayor tamaño madura sexualmente.

JANTHINIDAE SEA-SNAILS

Janthinidae is a group of sea-snails with a unique feature: they use their mucus to produce a bubble raft to float in the ocean. Some of them can produce a bubble per minute.

Violet sea-snail (Janthina janthina) (Picture: Roboastra).

Well, this family of gastropods is made up of individuals who may change sex. Like the clownfish, organisms are born male and then change to female.

BLUESTREAK CLEANER WRASSE

The bluestreak cleaner wrasse (Labroides dimidiatus) is a fish in which the sex change is triggered by some behavioural patterns.

Bluestreak cleaner wrasse (Labroides dimidiatus) (Picture: Darwin Books Cats).

There is usually a dominant male that keeps a harem of females, but if he dies, the dominant female will assume the position of the male in a few hours, courting other females although the change of sex can be extended for two weeks.

THE COMMON SLIPPER SHELL: WHEN SIZE MATTERS

The common slipper shell (Crepidula fornicata) is a marine snail in which the sex change is produced by the size of the animal. This molluscs are born male but, at a certain size, they become females.

They are very curious snails: they live stacked on the top of other animal, with larger organisms at the bottom. This means that the individual of the base is a female and males are above. Thus, when the female dies, the larger male becomes the female of the group.

Common slipper shell (Crepidula fornicata) (Picture: Dr. Keith Hiscock).

It is an exotic species in Spain, which could be living in the whole Galician coast. Anyway, its natural distribution area is North America.

THIS ALSO HAPPENS IN THE MEDITERRANEAN

Until now, we have explained species that live far from the place we life, but the truth is that this behaviour also happens in some Mediterranean species. Some examples are the starlet cushion star (Asterina gibbosa) and the ornate wrasse (Thalassoma pavo).

The ornate wrasse is one of the most colourful fishes in the Mediterranean sea. In that case, they are born females, but according to the sex ratio, they can change to males.

Ornate wrasse (Thalassoma pavo) (Picture: Matthieu Sontag, Creative Commons).

REFLECTION

If you are one of those who thing that sex change in human beings is unnatural, you have read some examples of animals that change their sex.

All you need is Biology is a LGTB-friendly blog and we love everbody equally. More love and respect, and less hate!

REFERENCES

• Acerca ciencia: Los animales que cambian de sexo 
• Alvarado, A (2010). Cambio de sexo en algunas especies animales. Revista Digital Universitaria, Vol. 11, núm. 8
• Catálogo Español de Especies Exóticas Invasoras: Crepidula fornicata 
• Darwin Book Cats: Fun Fish Fact: Some fish change sex
• Hickman, Roberts, Larson, l’Anson & Eisenhour (2006). Principios integrales de zoología. Mc Graw Hill (13 ed).
• Tree of life web project: An Exploration of the Clowfish
• National Geographic (2002, abril). A bordo de burbujas.
• Picture cover: Alexander Vasenin, Creative Commons

Zombie parasites: a reality of science fiction

Many horror films are based on organisms that have the ability to control the victim’s mind. In fact, there is some kind of real parasites and parasitoids which can control its host’s behaviour to guarantee its breeding. In this post, we will discuss some examples of those interesting parasites.

INTRODUCTION

Parasitism is a type of predation where an organism (parasite) extracts a benefit at the expenses of another one (host). The parasites have lost the ability to synthesize some essential molecules that get through hosts, as well as parasitism is a mandatory relationship. There are many types of parasites, but the most interesting examples are zombies parasites.

The parasitic zombies have in common the ability to control and modify the behavior and physiology of the host to guarantee its breeding. Can you find them in different taxonomic groups (fungi, protozoa, nematodes, arthropods…). There are differents mechanisms to fulfill its objective, but the most important are: control the behavior of the host or induce him to suicide.

BEHAVIOUR MODIFICATION

Glyptapanteles is a genus of parasitoid wasp that infects species of Lepidoptera Thyrinteina leucocerae in its larval phase. The larvae become caterpillars which grow and feed normally. In the final stages of development of the caterpillar,  the pupae of parasitoid wasp (the metamorphosis between larvae and the adult stage) are released and settled next to the caterpillar. Before his release, the pupae excrete an endocrine substance that modifies the behavior of the caterpillar forcing him to protect the small pupae. caterpillar stops feeding and move until the adult wasp emerges. At that time, the Caterpillar dies from starvation and exhaustion.

Thyrinteina leucocerae caterpillar protecting a group of pupae of Glyptapanteles sp. (Photo: José Lino-Neto)

Another example of  interesting parasitoid wasp, is the species Hymenoepimecis argyraphaga infecting Plesiometa argyra (a species of tropical spider). In this case, the female sticks to the abdomen of the spider its egg. When the hematophagous (which feed on blood) larvae hatches, injected a chemical substance that causes the host to create a cobweb that is capable of supporting the weight of the cocoon, rather than a cobweb to catch insects. The larvae then feeds the host until it dies and then create its cocoon in the cobweb. Then, it will transform into pupae and eventually will emerge as an adult.

Differences between a normal cobweb of Plesiometa argyra and a modified cobweb. Modified image of William G. Eberhard (Nature, 2000).

The above examples are parasitoids that they finally finished with the life of its host, but there are cases where once the parasitoid releases from the victim’s body, the host can continue to live. This is the case of the infection of the Ladybird Coccinella septempunctata by wasp species Dinocampus coccinellae. The  female wasp injects the eggs in the abdomen of the Ladybird that incubates them inside. When the larvae have been developed (without touching any host’s vital organ), are released and form a cocoon that will protect the Ladybird.  If the host gets to survive for seven days, when the larvae become adult Ladybug will recover and can continue with normal life cycle.

Coccinella septempunctata protecting a cocoon of wasp Dinocampus coccinellae. (Photo:Gilles San Martin)

INDUCTION TO SUICIDE

Myrmeconema neotropicum is a nematode that infects tropical ants of the species Cephalotes atratus. These ants are completely black, but when they are infected with the parasite, their abdomen becomes reddish. This change allows the host camouflaged with certain berries and confuse frugivorous birds. In addition, this parasite is being able to change the behavior of ant and force her to rise to clear and unprotected areas to be located by the predators. The birds are hosts intermediaries, since thanks to their excrement, they get a greater dispersion of the eggs of parasites.

Differences between the abdomen of a Cephalotes atratus normal and an infected. (Photo: Steven Yanoviak)

Another species of nematode, namely Spinochordodes tellinii, infects to crickets Meconema Thalassinum (Orthoptera) species. The larvae of the parasite are in the water and are ingested by mosquitoes (intermediate host). Mosquitoes are swallowed up by Crickets and once in the intestine, the nematode grows up to triple the size of the insect. When the parasite is adult, modifies the behavior of the host causing and induces him to commit suicide in the water. Thus, the parasite is free in its middle order to breed.

Cricket (Meconema thalassinum) infected with the nematode Spinochordodes tellinii. (Photo: Alastair Rae)

The flatworm or platyhelminth Leucochloridium paradoxum infects snails of the species Succinea putris. The host eats the larvae of the parasite that develops into the digestive tract of the host to give rise to the sporocysts (a kind of sacks that contain thousands of larvae, known as cercarias). The sporocysts are directed towards the tentacles of the snail’s eyes and causes a very exaggerated inflammation that resembles a caterpillar. They also induce a change in the behavior of the snail, leading him away from protected areas and forcing them to expose in places where it can be seen by the birds. The movement of the tentacles draws the attention of the birds that eat the snail and spread through their feces the cercaria (next state of maturation of the parasite).

Life cycle of Leucochloridium paradoxum from Ophiguris (2009). The second image shows a parasite in the tentacle of the snail (Succinea putris) imitating a caterpillar. (Photo by Dick Belgers)

Finally, but no less important, highlights the parasitic fungus Ophiocordyceps unilateralis infecting species tropical ants (Camponotus leonardi). The host ingests the spores of the fungus. Once in the digestive system, it induces a change in the behaviour of the Ant, forcing her to climb to high places where anchor with jaws. Once there, the spores germinate through the host’s exoskeleton to release their reproductive structures.

Ant infected by Ophiocordyceps sp. See the reproductive structures of the fungus out of the exoskeleton of the host. (Photo: Alex Wild)

Today, however, the mechanisms used by these parasites zombies information continue to be investigated. Do you think that they seem to beings from a horror film? No,  it is not science fiction. It’s our surprising nature.

REFERENCES

• Carl Zimmer. Mindsuckers. National geographic. November 2014.
• William G. Eberhard. Spider manipulation by a wasp larva. Nature. Num 406, 255-256. Juliol 2000. ISSN: 0028-0836.
• P. Hughes et.al. Extended Phenotype: Nematodes turn ants into birds-dispersed fruits. Current Biology. Vol 17. Num 7.
• Anand Varma. Zombie parasites. National Geographic: Nat Geo Live.
• Nat Geo Live. World’s deadliest: zombie snails. 
• Cover photo: Guilles San Martín.

They look like starfishes, but they aren’t: the brittle stars

Some month ago, we talked about starfishes and we said that there are some animals, which are also echinoderms, with which they can be easily confused. Well, in this post we will talk about these animals: the brittle stars. We are going to explain their features to distinguish them from starfishes and we are going to expose some Mediterranean species. 

THE BRITTLE STARS

The brittle stars or ophiuroids are a class of echinoderms with more than 2,000 living species, which live in all types of seafloor.

Brittle star (Picture: Jose Manuel Cubero, Biodiversidad Virtual).

What features do you have to pay attention to differentiate a brittle star from a starfish? Brittle stars have five arms, which are thin and sharply originate from the central disk. This feature is key to not confuse them with starfishes. Another characteristic you have to observe to differentiate brittle stars from starfishes is in the bottom (oral side) of the animal: the ambulacral grooves are closed and covered by plates. Furthermore, tube feet don’t have suckers because they are more involved in locomotion than in feeding. In fact, their arms are constituted by articulated ossicles (called vertebrae) that allow their displacement.

Having the arms so thin, where are their organs? The mouth is in the lower part of the body and is surrounded by plates acting as jaws. They have no anus, so products that are not digested are expelled through the mouth. All organs are located in the central disc. They use bursae to breathe, which are bags in which water enters and leaves. In addition, the reproductive organs are connected to these bags, so that they expel gametes with water (although some species incubate their offspring). Most species have separate males and females.

Anatomy of a brittle star (Picture: Animal Diversity Web).

Where can you observe brittle stars? Brittle stars normally live in rocky seafloor with low or without light, usually hidden in cracks, where they feed on suspension particles, but some of them are carnivorous and one species can catch fishes by using their arms as a cage.

SOME EXAMPLES FROM THE MEDITERRANEAN SEA

In the Mediterranean Sea, we can find about 34 brittle star species. Six of them are endemic and other 2 species are exotic. Here, we will explain 5 of them.

SMOOTH BRITTLE STAR (Ophioderma longicauda)

It is the largest species. It comprises a pentagon-shaped central disc (about 3 cm of diameter) with arms, which are a bit bony and are 15 cm long. It has a brown colour on the dorsal side and is lighter in the ventral side and arms. They can be find till 50-70 meters deep under rocks, in holes and cracks; but the young individuals can hide between seaweed. They feed on worms and bivalves, mainly during the night.

Smooth brittle star (Ophioderma longicauda) (Picture: Fernando Herranz, Educa Madrid).

COMMON BRITTLE STAR (Ophiothrix fragilis)

Common brittle stars have the whole body covered with long spines, which can take a variable colour (usually brown and grey tonalities). They can measure up to 12 cm. It is the most abundant in both hard and soft bottoms, up to 100 meters deep. It feeds on particles with the ambulacral system. Did you know that they can live about 10 years? A curiosity: if you take one of these brittle stars and let it fall to the bottom, it sinks with open arms, allowing you to distinguish it from the following species.

Common brittle star (Ophiothrix fragilis) (Picture: Animal Base).

BLACK BRITTLE STAR (Ophiocomina nigra)

Although it is similar to the previous species, it can be distinguished from the common brittle star by the fact that in this species the spines are only in the arms, are shorter and are laterally arranged. It also has a brown to black colour, while arms are lighter than the disk (measuring up to 2.5 cm in diameter). It lives in shallow, rocky and sandy areas. To differentiate it from the common brittle star, if you catch one of them and you let the brittle star to drop, the ophiurid sinks with arms folded upwards.

Black brittle star (Ophiocomina nigra) (Picture: Segrest Farms)

AMPHIURA CHIAJEI

It is a small brittle star, with his body normally buried in the mud, so that only shows the arms abroad, which are very long and are used to collect debris. Its color is orange red. It is usually found between 10 and 200 meters deep.

Amphiura chiajei (Picture: Anders Salesjö Photography).

ASTROSPARTUS MEDITERRANEUS

This brittle star can not be confused with any other: it has its entire body covered with granules and has a considerable size. It is of uniform grey colour. They live in deep rocky substrates, sedimentary continental shelf and over gorgonian between 50 and 200 meters deep.

Astrospartus mediterraneus (Picture: Ranenere).

REFERENCES

• Ballesteros E & Llobet T (2015). Fauna i flora de la mar Mediterrània. Ed. Brau
• Club de Buceo de Biología: Ophiocomina nigra
• Club de Buceo de Biología: Ophioderma longicauda
• Club de Buceo de Biología: Ophiothrix fragilis
• Coll M, Piroddi C, Steenbeek J, Kaschner K, Ben Rais Lasram F, et al. (2010) The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats. PLoS ONE 5(8): e11842. doi:10.1371/journal.pone.0011842
• Hichman, Roberts,Larson, l’Anson & Eisenhour (2006). Principios integrales de Zoología. Ed. McGraw Hill (13 ed).
• Martin P (1999). Claves para la clasificación de la fauna marina. Ed. Omega
• Riedl R (1986). Fauna y flora del Mar Mediterráneo. Ed. Omega
• Vàzquez, J & Maluquer-Margalef, J (coord.) (2014). Guia pràctica per conèixer la natura de Catalunya. IPCENA. Lleida. 576 p.
• Foto de portada: Animal Base

Ocean alert: Coral bleaching is massively happening!

We would like that the main picture of this post had been modified using Photoshop, but unfortunately this is not the case. Thanks to the project XL Catlin Seaview Survey, we now know that coral bleaching is massively happening. What causes coral bleaching? How does coral become bleached? Which is the importance of coral in the ocean ecosystems? These questions and more are answered in this post. 

WHAT IS CORAL BLEACHING?

Coral bleaching is the result of the expulsion of symbiotic algae living in the coral tissues (zooxanthellae), producing them to become completely white.

Coral before and after a bleaching event (Picture: Kendall Kritzik, Creative Commons).

The presence of zooxanthellae is frequent in marine cnidarians, especially in species that live in shallow waters, and they are the responsible of the greenish, bluish, yellowish or brownish colour of many coral species. In fact, each cubic millimetre of tissue of the host has 30,000 algae cells. These zooxanthellae are single-celled algae, usually dinoflagellates, that are able to live in mutualism with the coral. So, if zooxanthellae and coral live in mutualism, which are the benefits of this relationship? Coral gets the products of photosynthesis, organic carbon and nitrogen; while the algae receive nutrients, carbon dioxide, protection and a good position with access to sunshine.

Diagram of the location of zooxanthellae in a coral (Picture: Ocean Portal).

WHAT CAUSES CORAL BLEACHING?

Several causes of coral bleaching have been detected:

1. Increased ocean temperature. Climate change is the foremost responsible of the increase in ocean temperature and this is the main stress causing coral bleaching, but it is not the only one. The rise of temperatures may be also produced by El Niño phenomenon. With just an increase of 1ºC of the water for only one month, corals begin to become bleached.
2. Reduced ocean temperature. As warmer water ocean may produce coral bleaching, colder water may also produce these events. Some proofs support this idea: in January 2010, cold water temperature in Florida might have produced coral bleaching that resulted in coral death.
3. Runoff and pollution. Near-shore corals can be bleached due to the pollution carried by precipitation’s runoffs.
4. Freshwater inundation. Due to a low salinity produced by a freshwater inundation, corals may start bleaching.
5. Overexposure to sunlight. High solar irradiation causes bleaching.
6. Extreme low tides. Long exposures to the air can produce bleaching in shallow corals.
7. Disease. Diseases cause coral to be more susceptible.

All these causes produce a stress to the coral and, as a result, corals expel the algae living in their tissues.

HOW DOES CORAL BECOME BLEACHED?

When corals are in a healthy state, they are home to algae, so that they are in a symbiotic relationship. But, when corals are stressed, the photosynthetic machinery of algae produce toxic molecules that cause the corals to expel the symbionts. If the stress is not severe, corals can recover, but they become bleached in severe and prolonged stresses. As a result, corals death because they loose their main source of food and are more susceptible to disease.

Coral bleaching process (Picture: Great Barrier Reef Marine Park Authority, Australian Government).

MASSIVE CORAL BLEACHING EPISODES

Two worldwide episodes of coral bleaching were detected in the 1998 (which killed 16% of the coral reefs around the world) and 2010, but a recent study carried out by the NOAA and the University of Queensland confirm a more severe coral bleaching episode this year (2015). This new episode, which is triggered by El Niño of this year (together with the global change), is predicted to affect the 38% of the worldwide coral reefs, killing 12,000 square kilometres of reefs. The more altered zones will be Australia and the Pacific and Indian oceans.

Bleaching in American Samoa. The first picture (before) was taken in December 2014 and the second (after) in February 2015 (Picture: XL Catlin Seaview Survey).

Nevertheless, coral bleaching doesn’t only occur in massive episodes. Each year, during summer months, some limited coral bleaching is reported all over the globe.

WHY ARE CORALS IMPORTANT?

Despite the fact that coral reefs comprise less than 1% of the underwater ecosystems, they play a major role in the ocean. One quarter of marine life depends on coral because they are the nursery of the sea, so they are an important protein source for animals and humans. Moreover, they protect shorelines from waves and tsunamis. In addition, from an economical point of view, they are one of the most important places of tourist interest and support fishing industries. In fact, they provide food and livelihoods for more than 500 million people around the world.

WHAT CAN YOU DO?

All the activities you do to lessen your carbon dioxide production are good to prevent the Earth from global change and, therefore, are good to avoid coral bleaching. Keep doing like that! Share with us: which are the actions that you take to prevent global change? 

REFERENCES

• Australian Government: Coral bleaching 
• Brusca, RC & Brusca, GJ (2005). Invertebrados. Mc Graw-Hill (2 ed).
• Lohr, J; Munn, C; Colin, B & Wilson, WH (2007). Characterization of a latent virus-like infectionon symbiotic zooxanthellae. Journal of Applied Environmental Microbiology 73 (9): 2976-2981.
• Nature: Oceans and Coasts. Coral Bleaching: what you need to know
• NOAA: What is coral bleaching? 
• Ruppert, EE; Fox, RS & Barnes RD (2004). Invertebrate Zoology. Cengage Learning (7 ed).
• XL Catlin Seaview Survey: Global Coral Bleaching
• XL Catlin Seaview Survey: Global Reef Record

Tardigrades: animals with superpowers

The smallest bears in the world have almost superhero abilities. Actually, they are not bears: water bears is the popular name of tardigrades. They are virtually indestructible invertebrates: they can survive decades without water or food, to extreme temperatures and they have even survived into outer space. Meet the animal that seems to come from another planet and learn to observe them in your home if you have a microscope.

WHAT IS A TARDIGRADE?

Water bear (Macrobiotus sapiens) in moss. Colored photo taken with a scanning electron microscope (SEM). Photo by Nicole Ottawa & Oliver Meckes

Tardigrades or water bears, are a group of invertebrates 0.05-1.5 mm long that preferably live in damp places. They are especially abundant in the film of moisture covering mosses and ferns, although there are oceanic and freshwater species, so we can consider they live anywhere in the world. Even a few meters away from you, in the gap between tile and tile. In one gram of moss they have find up to 22,000 individuals. They are found in Antarctica under layers of 5 meters of ice, in warm deserts, hot springs, in mountains 6,000 meters high and abyssal ocean depths: they are  extremophiles. It is estimated that over 1,000 species exist.

MORPHOLOGY

Its popular name refers to their appearance, and the scientific name to their slow movements. Their bodies are divided into five segments: cephalic, with its tube-shaped mouth (proboscis) with two internal stilettos and sometimes simple eyes (ommatidia) and sensory hairs, and the remaining 4 segment with a pair of legs per segment. Each leg has claws for anchoring to the ground.

Bottom view of a Tardigrade where the five segments of the body are observed. Colored photo taken with a scanning electron microscope (SEM). Photo by Eye Of Science/Science Photo Library

Tardigrade (Echiniscus sp.) In which you can see the claws. Colored photo taken with a scanning electron microscope (SEM). Photo de Eye Of Science/Science Photo Library

Look at this video of Craig Smith to see tardigrade’s movements in more detail:

FEEDING

With its mouth stilettos, tardigrades perforate plants and absorbe the products of photosynthesis, but they can also feed absorbing the cellular content of other microscopic organisms such as bacteria, algae, rotifers, nematodes… Some are predators too and can eat whole microorganisms.

Their digestive system is basically the mouth and a pharynx with powerful muscles to make sucking motions that opens directly into the intestine and anus. Some species defecate only when they shed.

Detail of the mouth of a tardigrade. Colored image of scanning electron microscope (SEM). Photo by Eye Of Science/Science Photo Library

INTERNAL ANATOMY

They have no circulatory or respiratory system: gas exchange is made directly by the body surface. They are covered by a rigid cuticle which can be of different colors and is shed as they grow. With each moult, they lose oral stilettos, to be segregated again. They are eutelic animals: to grow they only increase the size of their cells, not their number, that remains constant throughout life

REPRODUCTION

Tardigrades generally have separate sexes (are dioecious) and reproduce by eggs (are oviparous), but there are also hermaphrodites and parthenogenetic species (females reproduce without being fertilized by any male). Fertilization is external and development is direct: they don’t have larval stages.

Tardigrade egg. Colored image of scanning electron microscope (SEM). Photo by Eye of Science/Science Photo Library

TARDIGRADE’S RECORDS

The tardigrades are incredibly resilient animals that have survived the following conditions:

• Dehydration: they can survive for 30 years under laboratory conditions without a single drop of water. Some sources claim that resist up to 120 years or have been found in ice 2000 years old and have been able to revive, although it is likely to be an exaggeration.
• Extreme temperature: if you boil one tardigrade survives. If you put it to temperatures near the absolute zero (-273ºC), survives. Their survival rate ranges from -270ºC to 150ºC.
• Extreme pressure: they are capable of supporting from vacuum to 6,000 atmospheres, ie 6 times the pressure in the deepest point on Earth, the Mariana Trench (11,000 meters deep).
• Extreme radiation: tardigrades can withstand bombardment of radiation at a dose 1000 times the lethal to a human.
• Toxic substances: if they are immersed in ether or pure alcohol, survive.
• Outer space: tardigrades are the only animals that have survived into space without any protection. In 2007 the ESA (European Space Agency) within the TARDIS project (Tardigrades In Space) left tardigrades (Richtersius coronifer and Milnesium tardigradum) for 12 days on the surface of the Foton-M3 spacecraft and they survived the space travel. In 2011 NASA did the same placing them in the outside of the space shuttle Endeavour and the results were corroborated. They survived vacuum, cosmic rays and ultraviolet radiation 1,000 times higher than that of the Earth’s surface. The project Biokis (2011) of the Italian Space Agency (ASI) studied the impact of these trips at the molecular level.

HOW DO THEY DO THAT?

The tardigrades are able to withstand such extreme conditions because they enter cryptobiosis status when conditions are unfavorable. It is an extreme state of anabiosis (decreased metabolism). According to the conditions they endure, the cryptobiosis is classified as:

• Anhydrobiosis: in case of environmental dehydration, they enter a “barrel status” because adopt barrel shaping to reduce its surface and wrap in a layer of wax to prevent water loss through transpiration. To prevent cell death they synthesize trehalose, a sugar substitute for water, so body structure and cell membranes remain intact. They reduce the water content of their body to just 1% and then stop their metabolism almost completely (0.01% below normal).

  

  Tardigrade dehydrated. Photo by Photo Science Library

• Cryobiosis: in low temperatures, the water of living beings crystallizes, it breaks the structure of cells and the living being die. Tardigrades use proteins to suddenly freeze water cells as small crystals, so they can avoid breakage.
• Osmobiosis: it occurs in case of increase of the salt concentration of the environment.
• Anoxybiosis: in the absence of oxygen, they enter a state of inactivity in which leave their body fully stretched, so they need water to stay perky.

Referring to exposures to radiation, which would destroy the DNA, it has been observed that tardigrades are able to repair the damaged genetic material.

These techniques have already been imitated in fields such as medicine, preserving rat hearts to “revive” them later, and open other fields of living tissue preservation and transplantation. They also open new fields in space exploration for extraterrestrial life (Astrobiology) and even in the human exploration of space to withstand long interplanetary travel, ideas for now, closer to science fiction than reality.

ARE THEY ALIENS?

The sparse fossil record, the unclear evolutionary relatedness and great resistance, led to hypothesis speculating with the possibility that tardigrades have come from outer space. It is not a crazy idea, but highly unlikely. Panspermia is the hypothesis that life, or rather, complex organic molecules, did not originate on Earth, but travelled within meteorites in the early Solar System. Indeed, amino acids (essential molecules for life) have been found in meteorites composition, so panspermia is a hypothesis that can not be ruled out yet.

Photo by Eye Of Science/Photolife Library

But it is not the case of tardigrades: their DNA is the same as the rest of terrestrial life forms and recent phylogenetic studies relate them to onychophorans (worm-like animals), aschelminthes and arthropods. What is fascinating is that is the animal with more foreign DNA: up to 16% of its genome belongs to fungi, bacteria or archaea, obtained by a process called horizontal gene transfer. The presence of foreign genes in other animal species is usually not more than 1%. Could be this fact what has enabled them to develop this great resistance?

DO YOU WANT TO SEARCH TARDIGRADES BY YOURSELF AND OBSERVE THEM IN ACTION?

Being so common and potentially livIng almost anywhere, if you have a simple microscope,  you can search and view living tardigrades by yourself:

• Grab a piece of moss of a rock or wall, it is better if it is a little dry.
• Let it dry in the sun and clean it of dirt and other large debris.
• Put it upside down in a transparent container (such as a petri dish),  soak it with water and wait a few hours.
• Remove moss and look for tardigrades in the water container (put it on a black background for easier viewing). If lucky, with a magnifying glass you’ll see them moving.
• Take them with a pipette or dropper, place them on the slide and enjoy! You could see things like this:

REFERENCES

• Pequeños pero invencibles
• Revelan más secretos del indestructible tardígrado
• Meet the miniature water bear: nature’s ultimate survivor or an alien from another planet?
• Tardígrados, los animales que desafían toda preconcepción biológica
• Tardigrada.es
• Los tardígrados, ositos de agua
• Tiny animal survive exposure to space
• Anhydrobiosis in invertebrates
• “Alien” water bears amaze scientists
• Tardigrada (Astronoo)
• La criptobiosis en el phylum Tardigrada
• El animal “más resistente de la Tierra” se prueba en el espacio
• Cover photo by Oliver Meckes

The nautilus: unusual cephalopods

Nautilus are, probably, one of the least known cephalopods, because their mates the squids, the cuttlefishes and the octopuses are present in fish markets and supermarkets and because they can be seen easily diving or snorkelling. Here, we will focus on their biology and some curiosities.  

INTRODUCTION: THE CEPHALOPODS

Nautilus are a group of marine animals that are included in the Cephalopoda class, which, together with the bivalvia (clams, mussels…), gastropoda (snails, nudibranchs…) and other less-known groups, constitute the molluscs, with about 90,000 extant species (and other 70,000 fossil species). Cephalopods are marine and predator animals. Instead of having the typical foot of the molluscs, they have transformed it into a funnel that expels the water of the body (and, therefore, they can travel for the water by propulsion) and in a crown of arms. Cephalopods have male and female individuals. To reproduce, males introduce a capsule containing espermatozoa (spermatophore) inside the body of the female using a modified arm called hectocotylus.

THE NAUTILUS

The nautilus, or rather nautiloidea, are a subclass of cephalopods characterized by the presence of a coiled, pearly, external shell, which is punctuated with chambers, as a result of their growth. These chambers are connected by a tube tissue called siphuncle, which permit the regulation of the buoyancy of the animal by the entrance or the release of water and liquid.

Individual of the genus Nautilus (Picture: Servando Gion).

Their body, placed in the outermost chamber with the body attached by muscles, present 47 pairs of tentacles, which lack suckers (but they produce adhesive substances), which take part in feeding and present several sense organs. Four of this tentacles, in the male are transformed into copulatory organs. The nervous system is diffused and they present a pair of eyes, which are relatively simple compared with other cephalopods. Like other cephalopods, the funnel permits to travel by propulsion. In case of threat, they can hide inside the shell thanks to the hood. For more anatomical details, watch the picture.

Anatomy of a nautiloid (Picture: Suggest Key Word).

They are nocturnal animals, which feed on deep-water crustaceans and fishes. They live in the tropical region of the Indian and Pacific oceans, close to the bottom, from near the surface to about 500 m depth.

Despite they were abundant in the past, during the Paleozoic and the Mesozoic, nowadays there are just two genera,  Nautilus (with 4 species) and Allonautilus (with 2 species). To identify them, we have to focus on the size of umbilicus, the central part of the shell (outside view): while in Nautilus is small, so that measures between 5 and 16% of the shell; in Allonautilus is big, so that measures the 20% of the shell. Other intern traits, like gills and the reproductive system, let their differentiation. Despite there are differences between the species, they measure about 23 cm of diameter and weigh about 1,5 kg.

Nautilus pompilius (left) and Allonautilus scrobiculatus (right) (Picture: Softpedia)

It is difficult to observe these animals. In fact, an Allonautilus scrobiculatus has been recently spotted after 30-year absence.

REFERENCES

• Brusca & Brusca (2005). Invertebrados. Ed. McGraw Hill (2 ed).
• Hickman, Roberts, Larson, l’Anson & Eisenhour (2006). Principios integrales de Zoología. Ed. McGraw Hill (13 ed)
• Jereb, P.; Roper, C.F.E. (eds). Cephalopods of the world. An annotated and illustrated catalogue of cephalopod species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. 2005. 262p.
• Malacologia.es: Biología de los moluscos