A remarkable new genus and species of fan worm (Polychaeta : Sabellidae : Sabellinae) associated with marine gastropods

A new genus and species of South African sabellid polychaete, Terebrasabell a heterouncinata, is described. The species lives in burrows in living gast ropod shells and was first discovered in 1993 in red abalone aquaculture fa cilities in southern California. Shell abnormalities in cultured abalones, caused by heavy sabellid infestations, raised concerns about its potential impact on native gastropods. The species has eight thoracic and three abdom inal setigers, and is distinguished by the following features: 1) two pairs of radioles; 2) uncini in thoracic setigers 2-6 acicular, with main fang s urmounted by small teeth, companion setae present; 3) uncini in thoracic se tigers 7-8 avicular, with no main fang and teeth in a rasp-like (serpulifor m) arrangement; 4) abdominal uncini acicular with main fang surmounted by s mall teeth. Members of T. heterouncinata are simultaneous hermaphrodites, w ith sperm produced in setiger 8 and oocytes in setigers 9-10. Sperm have an elongate nucleus and short midpiece. Young are brooded in the adult burrow to a late larval stage with about 6 setigers, but are nonfeeding, lacking a branchial crown. Released larvae crawl over the surface of the mollusc ho st shell and settle under the shell lip, in contact with the mantle tissue. Larvae are subsequently covered by shell from the host, forming the burrow , Crown formation and feeding commence after burrow formation. Cladistic an alyses support the hypothesis that Terebrasabella is most closely related t o Amphiglena, as part of the apomorphic Sabellinae clade, (Laonome (Terebra sabella, Amphiglena)). The early release of late-stage, non-feeding larvae, which enables the association of T. heterouncinata with gastropods,:appear s to have been independently derived in this species as well as several Amp higlena species.