THE INDO-PACIFIC GEMMULA SPECIES IN THE SUBFAMILY TURRINAE: ASPECTS OF FIELD DISTRIBUTION, MOLECULAR PHYLOGENY, RADULAR ANATOMY AND FEEDING ECOLOGY.

The biology, feeding ecology and phylogenetic relationships of marine snails in the family Turridae remain poorly understood. Here we report our study on four deep-water species in the genus Gemmula, a major group in this family. The four species G. speciosa (Reeve 1843), G. sogodensis (Olivera 2005), G. kieneri (Doumet 1940) and G. diomedea (Powell 1964) were collected at five different sites in the Philippines, and their pattern of distribution in the sites, their feeding behaviour as well as their phylogenetic relationships with each other and with other members of the subfamily Turrinae were investigated. The radular morphology (of two Gemmula species) and potential prey (for one Gemmula species) were also examined. Actual feeding observations were also conducted for Gemmula speciosa and compared with two turrids from other genera.All four Gemmula species showed strikingly different patterns of distribution; each species was found to be relatively much more abundant at one site but not at the other sites. Molecular phylogenetic analysis based on 16S sequences correlated with previously reported 12S sequences and revealed that the four species all belong to a well-supported Gemmula clade within the subfamily Turrinae; and that this clade appeared more closely related to the clades Xenuroturris, Turris and Lophiotoma than to the other clades in the subfamily (i.e., Turridrupa, Unedogemmula and Polystira). Morphological analysis of the radula of both G. speciosa and G. sogodensis revealed that the radulae of the two species were similar but differed from the other turrids, Lophiotoma acuta and Unedogemmula bisaya, by the absence of central teeth, consistent with the separation of the Gemmula clade from the Lophiotoma and Unedogemmula clade.To identify the polychaete group that is targeted as prey by species of Gemmula, analysis of regurgitated food fragments was made; phylogenetic analysis of an mtCOI gene fragment that was PCR-amplified from the regurgitated tissue of one specimen (G. diomedea) indicated close affinity of the prey to the terebellid polychaete Amphitritides. Specimens of Gemmula speciosa, when challenged with the terebellid polychaete Loimia sp., were observed to attack the worm suggesting that Gemmula species feed on terebellid polychaetes. Lophiotoma acuta were also observed to feed on the same species of terebellid but were usually group-feeding in contrast to the solitary feeding of G. speciosa. Unedogemmula bisaya did not feed on the terebellid which also supports the separation of the Gemmula and Unedogemmula clade.Two lines of proof (i.e. the molecular phylogenetic analysis and the feeding challenge) supporting the toxin homology findings previously reported, provide consistent evidence that Gemmula is a distinct clade of worm-hunting Turrinae that feeds on Terebellidae.