Tylodina perversa is an opisthobranch species quite common in the Costa Brava (NE Spain), especially on sponges Aplysina (Verongia) aerophoba that are found in very shallow water.
Although it has been always considered carnivorous -it is always found feeding on the same type of sponges-, a more detailed study put this fact in jeopardy. Every indication shows that the opisthobranch consistently prefers the sponges with a greater ammount of cyanophyte algae.
Thus, in the article “Tylodina perversa: una oveja disfrazada de lobo” (“Tylodina perversa: a sheep disguised as a wolf”) (1), this is stated: “Our study shows that T. perversa actively selects both sponges and sponge zones with a higher concentration of cyanobacteria [symbionts] implying that a large percentage of the ingested food is not of animal origin. ”
Of course, the lemon-yellow colour of this animal, of exactly the same shade as the sponge on which it is found, is obtained from the sponge, so T.perversa certainly takes advantage of the pigments of the sponge. It does not feed on algae exclusively.
The discussion is set.(1) Turon, X. Becerro, M.A. y Uriz, M.J: “Tylodina perversa: una oveja disfrazada de lobo” en el libro de resúmenes del XI Simposio Ibérico de Estudios del Bentos Marino [168-169]. Málaga 2000