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[[ Trimma ]]

Discussion

Several studies have been published detailing the osteology of various gobioid genera (e.g. Birdsong, 1975, Microgobius ZBK ; Gill and Hoese, 1993, Paraxenisthmus ZBK ; Mesterman and Zander, 1984, Pomatoschistus ZBK - but including only the caudal structure of the vertebral column; Miller, 1973, Rhyacichthys ZBK ; Murdy, 1985, Istigobius ZBK ; Springer, 1988, Rotuma ZBK ). A much larger number of publications deal with selected osteological features of these fishes; these are often comparative in nature and aimed at elucidating phylogenetic relationships (e.g. Akihito, 1963, 1967, 1969, 1971; Birdsong et al., 1988; Harrison, 1989; Larson, 2001; Murdy, 1989; Pezold, 1993; Scsepka et al., 1999; Springer, 1983; Winterbottom, 1990).

Birdsong et al. (1988) placed Trimma in their Priolepis ZBK Group, a large assemblage of genera the species of which dominate the coral reefs of the Indo-Pacific. This group is defined by a dorsal pterygiophore formula of 3-22110, 26 vertebrae, a single epural and two anal fin pterygiophores anterior to the first haemal spine. The only taxon belonging to this assemblage for which all components of the osteology are described is Istigobius ornatus (Murdy, 1985) . Pezold’ s (1993) study of the monophyly of the Gobiinae, based on the oculoscapular pore configurations, unfortunately cannot be applied to certain genera currently assigned to those members of the Priolepis ZBK group which lack this structural complex - as Pezold noted. These include the “type” genus Priolepis ZBK , as well as Trimma , Trimmatom ZBK and Paratrimma ZBK . It should be noted that the Priolepis ZBK group itself may not form a monophyletic assemblage. For example, both Thacker and Cole (2002) and Thacker (2003) conclude from studies of DNA sequences that the two species of Fusigobius ZBK they examined, F. neophytus and F. signipinnis ZBK , belong in very different lineages. Note also that the issue of non-monophyly of Fusigobius ZBK itself was not specifically addressed by Thacker and Cole (2002), who stated that resolution of this issue would have to await revisionary studies of the species currently assigned to that genus. However, they did demonstrate that neither species of Fusigobius ZBK was particularly closely related to Coryphopterus ZBK , as maintained by Randall (1995).

Within Trimma (itself not currently strongly defensible as a monophyletic assemblage even with the inclusion of Trimmatom ZBK - see Winterbottom, 1990), null hypotheses can nevertheless be erected for two apparently monophyletic subsets. One of these is the Trimma caesiura ZBK complex, defined by a very steep-sided trench between the orbits that continues around the posterodorsal margins of the eye (see Winterbottom and Villa, in press, for a list of nominal species included and a more detailed description and illustrations of these structures); the other is the T. tevegae ZBK complex (nominal species: T. tevegae ZBK , T. taylori ZBK , T. hoesei ZBK , T. griffithsi ZBK and probably T. winchi ZBK ), defined by a much broader, flat, bony interorbital region, a better developed rostral cartilage, extensive bony contact between the posteroventral process of the symplectic and the anterodorsal process of the preopercle, and greatly expanded haemal canals in the first few caudal vertebrae (see figs. 26 and 27 in Winterbottom, 1984, of Trimma taylori ZBK and T. griffithsi ZBK respectively). There are numerous undescribed new species in both of these complexes.

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