The bryozoan genus Arbocuspis (Cheilostomata, Electridae) from the Indian Ocean, with description of a new species from off southwestern Thailand, Andaman Sea

Abstract

Arbocuspis is a bryozoan genus, so far lacking a fossil record. It includes a few, essentially intertropical, living species, all until recently considered as mere varieties of the genotype species Membranipora bellula Hincks, 1881. Scanning electron microscope images of type material are presented for the first time for Arbocuspis bicornis Hincks, 1881 from Ceylon and Arbocuspis multicornis Hincks, 1881 from Australian waters, together with a modern description for this latter species. A new species, Arbocuspis emanuelae n. sp., is erected for specimens from the Andaman Sea. Arbocuspis emanuelae is easily distinguishable from congeners because of its two symmetrically branching spines overarching the opesium, and the group of pointed unbranched spines between them. Species of Arbocuspis are especially adapted to colonise shallow-water habitats and ephemeral substrata, and their apparently wide distributions possibly result from natural and/or anthropogenic-mediated transport, and/or also point to complexes of cryptogenic species. The diagnosis of the genus is amended owing to the occurrence in A. emanuelae n. sp. of several kinds of kenozooids, which were unreported from previously known species.