Deep-sea vesicomyid clams from hydrothermal vent and cold seep environments: Analysis of shell microstructure

The shell structure of five vesicomyid clams (i.e., Vesicomya species A, V. species B, V. species C, V. species D, and V. species E) from deep-sea hydrothermal vent and cold sulfide/methane seep environments is characterized by scanning electron microscopy (SEM). SEM examination of fractured and sectioned specimens reveals an array of shell microstructures in distinct arrangements. The shell of V. species A contains the most layers (7) and exhibits microstructure patterns markedly different than those of the other four vesicomyid species. The shell microstructure patterns of V. species B and V. species C, although similar, also show important differences. For example, fine spherulitic structure is exclusively found in V. species B, and "coarse" complex crossed lamellar structure only occurs in V. species C. Vesicomya species D and V. species E likewise exhibit similar shell microstructure patterns, although V. species D has an inner fine complex crossed lamellar layer not found in V. species E, and V. species E has an inner irregular complex crossed lamellar layer not present in V. species D. The shell microstructure patterns in the aforementioned species vary from those of previously described deep-sea vesicomyids (i.e., Calyptogena magnifica Boss and Turner, 1980; C. phaseoliformis Metivier, Okutani and Ohta, 1986; and C. cf. pacifica Dall, 1891). Results of these investigations indicate that shell microstructure analysis may be of great value in taxonomic studies of the Vesicomyidae.