Characteristics of larval and juvenile development in the deep-sea mussel Adipicola pacifica inhabiting whale bones in symbiosis with chemoautotrophic bacteria

In order to understand bivalve life history traits it is necessary to understand the characteristics of the habitats they occupy. Deep-sea bivalves belonging to the families Vesicomyidae and Mytilidae, thrive in deep-sea hydrothermal vents, cold seeps, and are even found on whale carcasses living in symbiosis with chemoautotrophic bacteria. In the latter instance, there is little information on life histories especially for reproductive and developmental strategies. In contrast to most shallow and deep-sea marine environments, the chemosynthesis-based environment can be regarded as unstable due to the temporary nature of the type of habitat in terms of space, chemical composition and time of existence. Reproductive strategies and variations in sexual expression adopt each species to its particular habitat, ensuring reproductive and developmental successes. Ontogenetic studies have been carried out on the mussel Adipicola pacifica (Bivalvia: Mytilidae) on submerged lipid-rich whale bones. We investigated the morphological changes in development from swimming larva to juvenile. This is the first report referring to the larvae in the whale-bone-attached mussel. A. pacifica has a planktotrophic larval stage. The larval life spans were approximately 2-months under experimental conditions. The planktonic larvae of this species can have a long residence time. In the swimming larval stage, just before settlement, the coloration of the larval shell (the prodissoconch) was red to brown. While the velum was lost, the colored prodissoconch remained on the newly developing shell in the settled juvenile. As such this species could be easily identified from others. The long larval period of this species is likely to assist in wide disperse and gives them the opportunity to reach other whale bones at the sea bottom.