Descriptions of mytilid species and definition of the Dacrydiinae n. subfam. (Mytilacea-Bivalvia)

Abstract

Abstract Ten mytilid species are described as new, viz. Modiolus (Modiolus?) nicklesi (tropical W. Africa), M. (M.) pseudobarbatus (tropical W. Africa), M. (M.) thorsoni (tropical W. Africa), Musculus (Musculus) koreanus (Sea of Japan), Rhomboidella obesa (tropical W. Africa), R. malaccana (W. coast of Thailand), Xenostrobus mangle (W. coast of Malaysia), X. balani (W. coast of Thailand), Dacrydium angulare (S. Atlantic), and D. viviparum (Reykjanes Ridge). The latter species has suprabranchial protection of embryos as does the Mediterranean D. hyalinum (Monterosato). Modiolus lulat (Dautzenberg, 1891) is regarded synonymous with M. martorelli (Hidalgo, 1877), and Vignadula Kuroda & Habe, 1971, with Xenostrobus Wilson, 1967. — The descriptions include anatomical and biological notes for several of the species. — The so-called ‘periostracal’ hairs of mytilids are concluded to be secretions of byssus glands, shaped and applied to the shell exterior by the foot of these bivalves. — It is pointed out that the opisthodetic, parivincular ligament of mytilids is separate and secondary in ontogeny. — Species of the Dacrydiinae n. subfam. are characterized by a non-nacreous shell which is homologous with the nepioconch of other mytilids, by functional persistence of the primary ligament and absence or ontogenetically late formation of a weak secondary ligament, by simplification and, in part, reduction of the soft parts. They are thus neoteneous in several respects. The group is briefly discussed and a survey of taxobases is given.