Taxonomy of and biological notes on the bivalve genusMicrogloma, with comments on protobranch nomenclature

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Abstract
The protobranch bivalve genus Microgloma Sanders & Allen, 1973 includes 3 or 4 minute species, shell length 0.85–1.1 mm. They are progenetic and their systematic position proposed herein, in the Nuculanidae (Nuculanoidea), is concluded from their similarity to young specimens of that family and sperm morphology. The genus was hitherto classified in Pristiglomidae (Nuculoidea). Microgloma pusilla (Jeffreys, 1879) occurs on the European continental shelf and slope from Iceland and Norway to the Mediterranean Sea at depths between 200 and 1200 m. Microgloma lumidula (Monterosato, 1880) (new synonym: M. lumerae Sanders & Allen, 1973) occurs from the Bay of Biscay and the Mediterranean Sea to the Canary Islands at depths between 200 and 2351 m. Phaseolus guilonardi Hoeksema, 1993 from the Netherlands and Atlantic France, is tentatively included in Microgloma (new combination). A few live M. pusilla were kept in the laboratory for nearly four years and the development of five young born there, was followed. Reproduction is characterized by simultaneous hermaphroditism and brooding of the embryo in a gonadal pouch. The young stay here after prodissoconch I has formed (length ca 200 µm) and continues to grow after the yolk of the egg has been consumed, presumably based on nutrition transferred from the parent. The young are released at a size of 400 µm, one at a time and after about 9 months of development. Some information is given on growth, longevity and mortality. The classification of the protobranch bivalves is briefly discussed and attention is drawn to several discrepancies in the names of families and their use.

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