The genera Bembicium and Risellopsis (Gastropoda: Littorinidae) in Australia and New Zealand
Abstract
The taxonomy of the Australasian littorinid genera Bembicium and Risellopsis is revised. Five Recent species of Bembicium are recognised: auratum, nanum, melanostoma, vittatum and flavescens, the first four of which occur on the Australian mainland, the last on Norfolk and Lord Howe Islands. B. melanostoma, B. vittatum and B. flavescens are sibling species which have been synonymised as B. melanostoma in recent systematic accounts, and are shown to be allopatric and distinguished mainly by characters of the penis. At least three fossil species of Bembicium are known, of which one is described as new, and the fossil record extends back to the late Oligocene or early Miocene. The genus is endemic to Australasia and presently extinct in New Zealand and the Kermadec Islands. The genus Risellopsis is monotypic, represented only, by R. varia in New Zealand, and has no fossil record before the Pleistocene. Systematic descriptions of the shell and animal and details of habitat and distribution are given for each species. These genera are abundant in the intertidal zone and the rather large literature on their biology and ecology is reviewed. Relationships with other littorinacean taxa are discussed. It is suggested that Bembicium and Risellopsis together form a monophyletic group, defined by synapomorphies of anterior salivary glands, anterior position of the junction of the duct of the seminal receptacle with the pallial oviduct, longitudinal division of the jelly gland and trochoidal shell shape. The littorinid genus Peasiella is superficially similar in shell characters, but anatomical features show that it is not closely related to Bembicium and Risellopsis. Interesting features of Bembicium include the type of development (the hatching of planktotrophic veligers from benthic egg masses recorded in two species is rare in the family) and the extreme intraspecific variability in the form of the radular teeth.
