Shell sculpture formation in bivalves of the genus Hiatella under different temperature conditions

Abstract

This study examines the effect of water temperature on the formation of shell sculpture in young molluscs of the genus Hiatella. The larvae of H. arctica and H. gallicana were maintained under laboratory conditions at different temperature regimes. The animals were reared from late veligers to juveniles with a shell length of 700 μm. The results of the experiment showed that the shell sculpture, which is a diagnostic species character, was developed to various degrees at different temperatures. The larvae of each species grew to juveniles with variously pronounced shell sculptures ranging from a complete absence of sculpturing to its maximum development. The individuals with smooth shells like those of H. gallicana were the most abundant among the molluscs reared at +5°С. At +12°С, all molluscs formed ridges and two rows of long spines in the posterior portion of the shell, which is typical for H. arctica. At +8°С, the molluscs developed various intermediate forms of shell sculpture. It was, therefore, demonstrated that the development and prominence of shell sculpture is determined by environmental temperature. These results are discussed with regards to the validity of using shell sculpture as a taxonomic character for species in the genus Hiatella.