An extended geographical distribution of Donax gemmula Morrison, 1971 (Bivalvia: Donacidae): new record from the Brazilian Northeastern coast

Abstract

This study provides the first record of Donax gemmula Morrison, 1971 (Bivalvia: Donacidae) from the Ceará State, Northeast Brazil; up to now it was only known from the Southeastern and Southern Brazilian coast. Shells larger than ~2 mm in length of this species can be distinguished from those of D. striatus Linnaeus, 1767. Both species were collected in the same beaches: Banco dos Cajuais and Pecém. The occurrence of D. gemmula remains unnoticed for others States of the Northeast Brazil, and so we suggest two possible explanations for this finding from Ceará State: i) a recent introduction (e.g., by ballast water); or ii) this species has a continuous distribution along the Brazilian coast (Ceará to Rio Grande do Sul), being not recorded until now because this is not easily collected (the animals are small and bottom samples need to be sieved to obtain them) and may be confused with young specimens of other species of Donax, such as D. striatus.