Thalasseleotrididae

Gill, Anthony C. & Mooi, Randall D., 2012, Thalasseleotrididae, new family of marine gobioid fishes from New Zealand and temperate Australia, with a revised definition of its sister taxon, the Gobiidae (Teleostei: Acanthomorpha), Zootaxa 3266, pp. 41-52 : 46-47

Thalasseleotrididae new family

Type genus. Thalasseleotris Hoese & Larson, 1987: 44 (feminine; type species Thalasseleotris adela Hoese & Larson 1987 by original designation and monotypy).

Diagnosis. Monophyly of the Thalasseleotrididae is supported by a single synapomorphy: membrane connecting the hyoid arch to ceratobranchial 1 broad, extending most of the length of ceratobranchial 1 (= first gill slit restricted or closed) ( Fig. 3 B). Among basal gobioids, only certain Eleotris Bloch & Schneider species (but not others) are known to have expansion of this membrane with some closure of the first gill slit, although not approaching the extent found in thalasseleotridids (Akihito 1967: figs 18–21). The membrane is, however, similarly developed in members of the gobiid genus Hetereleotris Bleeker ( Hoese & Larson 2005) , and in certain Eviota Jenkins species. Because none of these taxa is closely related to thalasseleotridids, we treat the occurrence of restricted or closed gill slits as homoplastic. Other gobioids either have the membrane confined to the extreme base of the first arch (near hypobranchial 1), or only extending to about one third of the length of certatobranchial 1 ( Fig. 3 A). In addition to this synapomorphy, the two included genera share a range of derived characters that are more broadly distributed among gobioid fishes, including: single epural; no mesopterygoid (= endopterygoid); vertebrae 10 + 15–17 (usually 10 + 16–17; note that McDowall’s 1965 counts for Grahamichthys exclude the urostylar complex, and thus are one fewer than reported here); first dorsal pterygiophore pattern 3-22110 or 3-22101 (formula follows Birdsong et al. 1988); anterior four middle + proximal pterygiophores of first dorsal fin closely applied to each other and tipped distally with cartilage; no bony trough in preopercle for support of laterosensory canal; head and anterior body naked (without scales).

Composition. Thalasseleotris Hoese & Larson 1987 (with two species, T. adela Hoese & Larson 1987 from temperate Australia, and T. iota Hoese & Roberts 2005 from New Zealand); Grahamichthys Whitley 1956 (with one species, G. radiata (Valenciennes in Cuvier & Valenciennes 1837), from New Zealand).

Remarks. A close relationship between Grahamichthys and Thalasseleotris was first noted by Hoese and Gill (1993), who suggested that the two genera form the sister group of the Microdesmidae (at that time defined to include the Ptereleotrinae ; we include both taxa in the Gobiidae ), although they retained them within their Eleotridinae. Earlier, in describing Thalasseleotris, Hoese and Larson (1987) noted similarity with the gobiid genus Hetereleotris , with which it shares 10 + 17 vertebrae and the first gill slit closed (see above). However, they recognized that it otherwise lacks gobiid specializations, and instead suggested a possible relationship with the Australian eleotridid genus Philypnodon Bleeker and the Australian-New Zealand genus Gobiomorphus Gill. Our studies do not support a close relationship between these two genera and thalasseleotridids.

We acknowledge that as an alternative to describing the Thalasseleotrididae , we could have simply classified the two included genera in the Gobiidae , which—given the sister relationship noted below—would have not affected the monophyletic status of the Gobiidae sensu lato. We have three primary reasons for not choosing this option. Firstly, such action would leave the Gobiidae (an important taxon in various biological and ecological studies) undiagnosed by external characters; in contrast, under our chosen option specimens can be identified to that family on the basis of one readily observed external character (number of branchiostegal rays). Secondly, inclusion of Thalasseleotris and Grahamichthys in the Gobiidae would have thrown the two genera into the morass that is the suprageneric classification of gobiids. This in turn would have ignored the sister-group relationship between the two genera and the Gobiidae . Thirdly, in order to reflect these relationships, it would ultimately be necessary to erect a family-group name for the two genera anyway (even if only at the subfamilial level).

Figures

FIGURE 3. Lower part of left side first branchial arch and hyoid arch in dorsal view showing degree of development of gill membrane (white) in: A) the odontobutid Micropercops swinhonis, same specimen as in Fig. 1; B) the thalasseleotridid Grahamichthys radiatus, same specimen as in Fig. 1. Abbreviations: ACH, anterior ceratohyal; CB 1, ceratobranchial 1; DHH, dorsal hypohyal; GM, gill membrane; HB 1, hypobranchial 1; PCH, posterior ceratohyal; VHH, ventral hypohyal. Gill rakers not illustrated. Scale bars = 1 mm.