Comparative Morphology and Redescription of Pleurobranchus Species (Gastropoda, Pleurobranchoidea) from Brazil.

Juliana Alvim and Alexandre Dias Pimenta (2016) The taxonomy of Pleurobranchus from Brazil is little known because the internal anatomy and possible intraspecific variation are poorly understood. This study recognizes three valid species from Brazil: Pleurobranchus areolatus Mörch, 1863, P. iouspi Ev. Marcus, 1984 and P. reticulatus Rang, 1832. Pleurobranchus reticulatus and P. areolatus were misidentified for a long time because of their simple descriptions, without photographs of living animals. However, they are distinguished by: color of the rhinophores, P. reticulatus has a uniform color, while P. areolatus has the same pattern as the dorsum; P. reticulatus is larger and has more pinnae free from the body wall than P. areolatus; the prostate is tubular and highly convoluted in P. reticulatus, while in P. areolatus is elongated with the proximal portion rounded; and, the jaws of P. areolatus, the smaller species, have more rows and fewer platelets per row than P. reticulatus. Pleurobranchus emys and P. iouspi are considered synonyms based on the examination of portions of the types, mainly due the presence of a dense layer of spicules in the mantle and because their original descriptions do not differ significantly. A discussion about some possible synonymies was provided and their recognition were based mainly on the diameter of the tubercles of the mantle, the presence/absence of flaps that surrounds the gonopore and the development of a leaflet in the convex portion of the penis. The detailed anatomical study allowed recognition of a general pattern in the position and presence or absence of extrinsic and intrinsic odontophore muscles for Pleurobranchus. The circulatory and nervous systems do not provide useful characters for species delimitation.