Identity of Crassostrea praia () and other oysters from Rio Grande do Sul, Brazil

The study aimed to identify species of the genus Crassostrea from Rio Grande do Sul and to trace the identity of C. praia, a species recognized under conchological or distributive precepts of native oyster species occurring in an ecological gradient beyond mangrove vegetation. To achieve this, oysters were collected in the southernmost region of Brazil (RS) for morphological and molecular identification of C. praia. The specimens were subjected to a diagnostic PCR-RFLP analysis and sequencing of the mitochondrial 16S rDNA gene. Based on the molecular identity of the specimens, a comparative anatomical assessment was made, involving the sizes of the mantle and the labial palps, the shapes of the accessory heart, heart, and anus, and pattern of the tentacles on the edge of the mantle. The molecular results showed the presence of two species in RS: C. rhizophorae and C. gasar, with the latter being a new occurrence for regions beyond mangrove vegetation. C. praia proved to be conspecific with C. rhizophorae, being its synonym. Anatomical data related to the species are plastic and incapable of generating specific criteria for identification between C. gasar and C. rhizophorae. Regarding the shell criteria used to promote the construction of the C. praia entity, they are deeply related to environmental conditions and the effect of population density on its conchological characters, since its molecular identity indicates that this species is synonymous with C. rhizophorae.