Curiosities about nudibranchs

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Flabellina affinis by Miquel Pontes

Flabellina affinis

The word “nudibranch” means “naked gills”. Derives from the Latin “nudus” (naked) and the Greek “brankhia” (gills). It refers to the small flower shaped protuberances that can be seen on the back of many of these animals.

There are more than 3,000 species of nudibranchs. They live from the surface to depths of 2,500 meters. They are found in all seas, from the tropics to the poles, although most inhabit the warm seas and shallow waters.

Many nudibranchs are poisonous while others pretend to be poisonous. Some acquire the stinging cells of the hydrozoans that they feed on and store them in their interior for protection. Many species of nudibranchs that eat sponges accumulate toxins in their bodies, so that they become toxic and inedible. Some nudibranchs even synthesize their own chemicals to defend themselves. All these species usually announce with bright colors on their bodies that they are dangerous, toxic or have a bad taste.

At least two species of nudibranchs are capable of making sounds audible to man. In 1884 Philip Henry Goose published observations of a Professor Grant on Facelina annulicornis and Dendronotus frondosus as capable of making a distinctive sound with his mouth, and repeating it at intervals.

Onchidoris neapolitana (2) by Enric Madrenas

Onchidoris neapolitana (2)

Many species of nudibranchs camouflage perfectly in their environment. This is because their survival strategy is to not be detected. Many species have not been discovered until recently because of it.

The nudibranchs are hermaphrodites. This means that they are male and female simultaneously. When they mate they fertilize each other to maximize their chances of survival. Then both lay eggs forming beautiful -usually spiralled- designs.

Some nudibranchs are “solar powered”. These species, usually classified as opisthobranchs, accumulate in their bodies the chloroplasts of the algae or corals from which they feed, so that they keep them active and able to perform photosynthesis when they are exposed to light, synthesizing nutrients that are used by the animal when there is no other food available. .

Most nudibranchs are benthic. They live crawling on the bottom of the sea, but some species like Phylliroe are pelagic, that is, they live in the water column and others like Glaucus live right on the surface.

Rinófor de Felimare picta by Miquel Pontes

Felimare picta, rinóforo

The “horns” of the nudibranchs are called rhinophores. Derived from the Greek “rhino”, nose, and “phore”, to carry, they are basically chemical receptors (we could say olfactory) that allow the animal to locate its food and other specimens to reproduce. A close up inspection reveals they have delicate structures designed to maximize the sensory surface exposed to water, increasing their ability to detect chemical substances. Having these protuberances on the body makes them vulnerable, so many species are able to shrink them inside the body when they are in danger.

Cannibalism exists in the world of nudibranchs. Some species feed on other nudibranchs, sometimes even specimens of the same species if no other food is available. The attack occurs by trapping its prey with the teeth of the radula, or absorbing and digesting it with digestive enzymes, depending on the species.

In some places of the world they eat nudibranchs. In Chile and some islands of Russia and Alaska roast or boil some species of nudibranchs, and even consume them raw. The texture has been described as “gummy”.

Miquel Pontes

Informàtic de profesió, és fotògraf submarí i naturalista aficionat. Submarinista des del 1994, el seu “logbook” compta amb unes 700 immersions al mar Mediterrani i als oceans Atlàntic, Índic i Pacífic. Ha participat i participa en tota mena de projectes divulgatius (llibres, revistes, webs, conferències, exposicions…) com a mitjà per difondre el seu interès principal: protegir els mars i els éssers que hi habiten. Fundador del Grup d’Estudis M@re Nostrum (www.marenostrum.org) Soci fundador del GROC (Grup Recerca d’Opistobranquis der Catalunya). Soci Fundador del VIMAR (Vida Marina). Va descobrir l’interessant mon dels opistobranquis el 1997 de la ma dels seus companys d’immersió i des de llavors ha estat una línia de treball continuada, aportant fotos submarines, observacions fetes al medi i donant suport informàtic per a la difusió d’aquests continguts.