Trimma

Richard Winterbottom, 2003, A new species of the gobiid fish Trimma from the Western Pacific and Northern Indian Ocean coral reefs, with a description of its osteology., Zootaxa 218, pp. 1-24 : 20-21

[[ Trimma ]]

Discussion

Several studies have been published detailing the osteology of various gobioid genera (e.g. Birdsong, 1975, Microgobius ; Gill and Hoese, 1993, Paraxenisthmus ; Mesterman and Zander, 1984, Pomatoschistus - but including only the caudal structure of the vertebral column; Miller, 1973, Rhyacichthys ; Murdy, 1985, Istigobius ; Springer, 1988, Rotuma ). 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 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 group which lack this structural complex - as Pezold noted. These include the “type” genus Priolepis , as well as Trimma , Trimmatom and Paratrimma . It should be noted that the Priolepis 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 they examined, F. neophytus and F. signipinnis , belong in very different lineages. Note also that the issue of non-monophyly of Fusigobius 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 was particularly closely related to Coryphopterus , as maintained by Randall (1995).

Within Trimma (itself not currently strongly defensible as a monophyletic assemblage even with the inclusion of Trimmatom - see Winterbottom, 1990), null hypotheses can nevertheless be erected for two apparently monophyletic subsets. One of these is the Trimma caesiura 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 complex (nominal species: T. tevegae , T. taylori , T. hoesei , T. griffithsi and probably T. winchi ), 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 and T. griffithsi respectively). There are numerous undescribed new species in both of these complexes.