The little world of sea slugs

Flamboyant dresses, mesmerizing dances, fleshy body and unbridled sexuality: all assets that would tantalize a man ... and yet it is our companions divers who are generally under the spell!

Dressed in their evening dress, sea slugs, these creepy little animals sport for many harlequin colors. Moreover, even our Mediterranean and Atlantic waters are populated by magnificent species that have nothing to envy to their tropical cousins. Close relatives of snails, these opistobranch gastropod molluscs (with gills behind the body) are mainly divided into two groups, in the middle of a classification that has often been modified:

≈ We find first of all a "super order" of the Tectibranches: their internal shell more or less visible is covered by parapodia (extensions of the foot). They are divided into several orders, the main ones are the Anaspidea (Aplysies or sea hares ...) and the Sacoglosses (Elysies, Thuridilles ...).

≈ The second group, much better known, is the order Nudibranchs (naked gills). They are shellless and have external gills, except for the suborder Eolidiens which breathe cutaneously and have papillae called cerates which increase the exchange surface.

Almost all individuals meet between the surface and 60m deep, in all environments: seagrass, seaweed, sand, rock, coralligenous, corals ...

The species of the shallows are not very colorful, which allows them to remain discreet more easily. Small Elysses store the chloroplasts of the algae they consume, and in the midst of which they live, camouflaged by their green color. Others, more colorful like flabellins, store in their cerates the cnidoblasts (stinging cells) of the hydraires they devour, which makes them urticant in turn. Nothing like to defend yourself!

Deeper, their dresses are masked by the lack of light; only the beam of a lamp can reveal them ... There, it is a true festival of colors which awaits you. Many species are found on sponges, many of which feed on them. The Dalmatian dory eats only Petrosia ficiformis, the stone sponge that he grazes with his raspy tongue. It is sometimes a challenge for the amateurs to flush out: some species like the dory celestial measure only a few millimeters, and their colors are sometimes confused with their environment.

By diving from spring to autumn, you may have the chance to observe these slugs in full reproduction. Notice to prude minds! The sexual act of these hermaphrodites can last for hours, and repeat itself several times. Each individual can play the role of male and female. Sea hares breed in "rosaries" and form a chain of several individuals. The dories mate head-spades, because of the arrangement of their genitals on the right side. The following eggs are usually spaghetti or rolled ribbons. Sometimes, as in the case of celestial dories, spawning is done inside a sponge, in which the little ones will develop. Once you have learned how to find them (this can become an obsession ...), observe them well. you may have the privilege of attending a strange belly dance ...

Above all, do not touch them, they are small fragile beings.

Good "hunt" with the slug!

Anthony LEYDET - www.zesea.com

Article published in Water Seekers n ° 23