Tylodina perversa is a species belonging to the phylum Mollusca, class Gastropoda, Order Umbraculida, family Tylodinidae and genus Tylodina. This genus consists of a total of 7 species, among which we find Tylodina perversa. It lives predominantly in the waters of the Mediterranean Sea, where it can be found from the shallowest waters to 10-15 meters deep.
The body of Tylodina perversa has an intense yellow color, which it adopts from the sponges it feeds on. They can reach 3 to 5 cm in length. On the dorsal part of the body there is a thin, slightly conical but very flattened shell, also yellowish in color, with radial brown stripes. The shell is often covered by some algae. Behind the shell, and when the animal is competently distended, we can observe a feather-like structure on the back right side of the animal, which corresponds to the gill with which it performs gas exchange. The mantle of this mollusc is larger than the shell itself, and at the front we will find between the mantle and the shell the cephalic region composed of a pair of long rhinophores, at the base of which we can observe two black dots that are its eyes. Also on the head we can find two short oral tentacles with a slightly triangular shape.
The diet of Tylodina perversa is strongly based on the yellow sponge Aplysina aerophoba, from which, as previously mentioned, it acquires the pigments (urandine) that give the coloration to this mollusc. Such is the incorporation of these pigments from the sponge in the body of the mollusc, that the specimens of Tylodina perversa will pass completely unnoticed on these sponges, and we will have to observe them very carefully to be able to observe them.
Regarding the reproduction of this species, the specimens are hermaphrodites and require cross sperm exchange. After fertilization, the specimens lay clutches, also of intense yellow color that go unnoticed on the sponges, and that adopt a semicircular shape with a slightly irregular surface.Photos: