Morfologia comparada de moluscos bivalves da Amazônia direcionada à taxonomia e sistemática filogenética de Hyriidae (Mollusca, Bivalvia, Unionoida)

Abstract

Despite the existence of works on the continental malacofauna from South America, knowledge of the native freshwater mussels of the order Unionoida in the region, especially the Amazon, is still limited. Works on modern systematics have been used for some species from the region, but the classification of taxa of South American Hyriidae is not yet established, and little is known about their anatomy and larvae. In order to enhance our understanding of species of unionoids from genera of the Amazon region and hypothesize relationships among Hyriidae from South America, shells, glochidia and morphology of soft parts were compared. The species studied were Diplodon suavidicus, D. obsolescens, D. hylaeus, Paxyodon syrmatophorus, Prisodon obliquus, Triplodon corrugatus, T. chodo, Castalia ambigua, Castalia quadrata and Callonaia duprei. The material comes from recent collections in rivers and lakes of the Brazilian Amazon basin and also specimens deposited in scientific and private collections. From the glochidia were were described the hook, the outer surface and the outlines of the larval shell. For the conchological study, the adult shells were measured and morphologically compared. Internal anatomy was described from dissected fixed specimens. Glochidia, internal anatomy drawings, outer surface of the periostracum and shell layers of adults were observed by SEM and optical microscope or estereomicroscopic with a digital camera. A phylogenetic nalysis was carried out using a matrix generated from morphological characteristics (shells, larvae, soft parts, ultrastructure) of nine species of South American Hyriidae. Both glochidia and analysis of morphology and morphometry of soft shells revealed important characteristics that distinguish between de Hyriidae genera analyzed. Diplodon suavidicus and D. obsolescens presented glochidia with a hook, thus belonging to the subgenus Diplodon s.s. Diplodon hylaeus, presenting a glochidium without a hook, was included in Diplodon (Rhipidodonta). Spines on the outer surface of the glochidial shell were unique to Paxyodon syrmatophorus and Prisodon obliquus. With regard to the adult shells, the species were recognized by the outline, macro and microscopic ornamentation, prisms from the prismatic layer and the relative widths of the prismatic and nacreous layers. The general organization of the prismatic layer was that of a composit prismatic structure with first order prisms perpendicularly grouped at the top forming a seemingly simple and compact structure and second order prisms visible in the bottom layer, forming a fibrous structure with fine and elongate crystals, diverging downward from the central axis. A new hyriid species from the Amazon, Triplodon chodo, was described from the analysis of shells. The anatomy of Diplodon obsolescens, Prisodon obliquus, Triplodon chodo and Castalia quadrata was described for the first time. Structures such as the presence of secondary papilla in front of the anus and the thickness of the mantle near the anterior gill were unique for Castalia. Interlamellar connections were useful to distinguish Diplodon from Castaliini and Prisodontini. Prisodon obliquus and Paxyodon syrmatophorus both have papillae in the posterior wing region that have not been observed in any other unionoids to date. Finally, a phylogenetic proposal for South American Hyriidae genera based on morphological characters showed that Castalia and the Prisodon-Paxyodon group are monophyletic.