Occurrence and histological characterization marsupia of Diplodon expansus (Küster, 1856) (Mollusca, Bivalve, Hyriidae) in Piraquara River, Parana, Brazil

In limnic bivalve individuals from the family Hyriidae, the gills have, besides the functions of gas exchange and feeding, an important function in the reproductive cycle. The gills undergo changes, resulting in a specialized structure, the marsupium, where the development of larva named glochidia occurs. This study aimed to determine the occurrence and morphological characteristics of marsupia of Diplodon expansus. Six bimonthly samples were carried out between May 2007 and May 2008, in Piraquara River, with capture of 180 specimens larger than 25mm. The total length of the shells was measured to determine the frequencies of size classes. Having predetermined morphological characteristics as a basis, the marsupia were classified into stage I and II. Tissue fragments of marsupia and visceral mass underwent a routine histological approach and they were embedded in paraffin. Nine length classes were recorded, with a 3 mm interval, and the modal class ranged from 50 to 53 mm. Marsupia in stages I and II were observed in 86% of females. Histological observations indicate that marsupia are permanent structures in mature females and that the population of D. expansus has a continuous reproductive strategy, with peaks of glochidia release.