During studies of mangrove communities in central Vietnam (Nhatrang Bay, Tre Is and Dam Bay) a heterosexual pair of pontoniine shrimp, Neoanchistus cardiodytes, was found in the mantle cavity of the deeply burrowing bivalve Mactra grandis (Mactridae). This is the fourth record of pontoniine shrimps in symbiosis with burrowing bivalves, the second record of this species as well as its first record from Vietnam and the Pacific Ocean. A representative of the family Mactridae is firstly reported as a host for pontoniine shrimps and a new host for N. cardiodytes.

The rayed trough-shell Mactra corallina Linnaeus 1758 is a surf clam that inhabits the Atlantic Ocean, Black Sea and Mediterranean Sea and represents a commercially important bivalve. This species is present with two different and well-defined sympatric morphotypes, which differ mainly for the colour of the shell (white in the corallina morph, and brown-banded in the lignaria morph). The aim of this work is to resolve the confused and contradictory systematics of the bivalves belonging to M. corallina putative species by analysing molecular and morphological features. Fifteen specimens of M. corallina corallina (white variant) and 19 specimens of M. corallina lignaria (brown variant) were collected in the North Adriatic Sea and analysed by four molecular markers (12S, 16S, 18S and COI genes, partial sequences). Genetic analyses clearly support the presence of two different species, which were previously ascribed to M. corallina. In addition, 35 specimens identified on a morphological basis as M. c. corallina and 28 specimens identified as M. c. lignaria collected in the same area were used for a morphometric analysis. A positive correlation was found between the maximum width of shell (W), antero-posterior length and between W and the height of specimens from umbo to ventral margin, thus adding to molecular data.