Larval shell development of four species of New Zealand mussels: (Bivalvia, Mytilacea)

Abstract

Larvae of Mytilus cdulis aoteanus, Perna canaliculus, Xenosirobus pulex, and Modiolarca impacta were reared to settlement in the hatchery. A detailed comparative study, based on microscopy (optical and SEM) and morphometry, has been carried out on the four species. External features and the internal hinge structure of the larval shells of the four species show typical mytilid characteristics. Externally, umbo stage larvae of Modiolarca impacta are ovoid in the anterio‐posterior direction, shell heights are substantially less than lengths, umbones are low and broadly rounded, and the anterior end is more pointed than the posterior. Mytilus edulis aoteanus and Perna canaliculus umbo stage larvae are similar, initially ovoid in the anterioposterior direction and later more rounded with shell heights approximately equal to lengths, umbones broadly rounded. The shoulders of P. canaliculus larvae are higher and more angular than those of M. edulis aoteanus. Xenostrobus pulex larvae are round to ovoid in the dorsoventral direction. Shell heights are equal to or greater than lengths, umbones are knobby. Prov‐inculum lengths and shapes are similar in Modiolarca impacta, M. edulis aoteanus, and P. canaliculus. Provinculum length is shorter and the shape distinctive in X. pulex. The provincular teeth number in larvae 200–299 μm long is 16–24 in Modiolarca impacta, 18–24 in P. canaliculus, 20–30 in M. edulis aoteanus, and 10–15 in X. pulex. The primary lateral hinge teeth in pediveliger stage larvae of P. canaliculus do not develop in the other three species.

Keywords:

• bivalve larvae
• Mytilidae
• larval shell development
• larval morphology
• mussels
• Mytilus edulis aoteanus
• Perna canaliculus
• Xenostrobus pulex
• Modiolarca impacta