Studies on deep-sea Protobranchia (Bivalvia); the family Malletiidae H. L. Sanders Woods Hole Oceanographic Institution, Woods Hole, Mass., 02543, U.S.A. J. A. Allen University Marine Biological Station, Millport, Isle of Cumbrae, Scotland. Contents Synopsis 195 Introduction 195 Family Malletiidae 196 Malletia 197 Minormalletia 197 Malletiella 197 Malletia abyssorum 197 Malletia johnsoni 205 Malletia grasslei (new species) 211 Malletia surinamensis (new species) 213 Malletia malita (new species) 217 Malletia pallida 220 Malletia polita 222 Malletia cuneata ............ 227 Malletia obtusa 232 Other species 234 Discussion 234 References 236 Appendix 238 Synopsis This paper redefines the deep water protobranch bivalve family Malletiidae and describes the functional morphology, growth and geographical distribution of nine species obtained from abyssal and slope depths of the Atlantic. Three new species are described, all from the Guinea Basin. Subtle differences in the shell shape between different populations are, where possible, quantified and described. The differences are discussed in relation to reproduction and isolation, and taking into account possible slow rates of gene flow and the emergence of sibling species. Introduction This is the fifth paper in a series on the biology and ecology of the deep-sea protobranch bivalves of the Atlantic (Allen & Sanders, 1973, 1982; Sanders & Allen, 1975, 1977). Our interest lies in a multiplicity of aspects of the life and evolution of these molluscs, (Allen, 1978), but in particular we have endeavoured to determine the adaptations of these animals to conditions at great depths. Supported by N.S.F. Grants GB-6027, GA-31105, GA-36554, OCE76-20833 and 20/8837 and NERC Grant GR3/3915A. Woods Hole Oceanographic Institution Contribution No. 5696 Bull. Br. Mus. not. Hist. (Zool.) 49 (2): 195-238 Issued 19 December 1985
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