Taxonomia de espécies do gênero Elysia Risso 1818 (Mollusca: Gastropoda: Sacoglossa) do Brasil

Abstract

The genus Elysia Risso, 1818 compraises almost a third of all described species of the order Sacoglossa, which is represented by animals with unique evolutionary traits or rare in the animal world. In Brazil, eight valid species are recorded to date: Elysia canguzua, Elysia chitwa, Elysia evelinae, Elysia flava, Elysia ornata, Elysia serca, Elysia subornata and Elysia tuca. Even though numerous, the genus is poorly studied anatomically, with the most recent work focused only to the external morphology, coloration and radula. Thus, the morphological and anatomical characteristics of the described species are not known enough to determine synapomorphies, which characterizes Elysia as a paraphyletic genus. In order to add information to understand the complex of the genus Elysia, we performed a detailed characterization of the digestive, reproductive and nervous systems, as well as external differentiation of the species found. Two species not formally named for Science were described and compared with valid species. Morphological features, such as the presence of ornamentation, pericardial hump length and anastomosis dorsal shape of the parapodia, are important for species identification. The color differs mainly in the presence of black, blue and orange pigments. The reproductive system is differentiated by the type of system (androdiaulic or triaulic), the number of hermaphrodites The reproductive system is differentiated by the type of system (or androdiáulico triáulico), the number of hermaphrodite ampoules, the occurrence of genital receptacle and its connection with the oviduct, the shape the prostate gland and the penis and the duct’s arrangement. The digestive system, although very similar among species, differs mainly in the form of the buccal mass and the ascus’ position, the size of the esophagus and esophageal pouch, the occurrence of folds in the stomach and intestines and the position of the anus. Radula, although not being a strong diagnostic characteristic for the identification of Elysia, provides valuable information about the species. The nervous system had also an important role in species identification, by distinct the size of ganglia, commissures and nerves. The addition of these data together with photographs of living specimens and electron microscopy of the radula, make this work updates the knowledge about the species found in the last century in the country. Although many recent studies show the importance of photosynthetic capacity, molecular approach or larval development in Elysia’s complex to solve the paraphilia status of the genus, the anatomy and morphology proves crucial in this process.