Glossogobius

Hoese, Douglass F., Allen, Gerald R. & Hadiaty, Renny K., 2017, Description of three new species of dwarf Glossogobius from New Guinea and northern Australia, Cybium 41 (2), pp. 179-193 : 181-182

Glossogobius

Glossogobius Gill, 1860: 46 (type species: Gobius platy-

cephalus Richardson, 1846: 204, 318, China, by monotypy).

The genus has been defined and postulated to be related to Psammogobius and Bathygobius ( Hoese and Allen, 2009; Hoese et al., 2015). Molecular studies support the relationship of those genera ( Agorreta et al., 2013). The genus is characterised by a distinctive longitudinal papilla pattern, 26-29 (rarely 25) vertebrae and a bilobed tongue. The present paper brings the total number of recognised and described species to approximately 38. One of the species described here is different from all other known Glossogobius in normally having only 26 vertebrae.

The species described here are dwarf species, maturing at about 20 to 30 mm SL and reaching a maximum size of less than 50 mm SL, making them the smallest in the genus along with Glossogobius bellendenensis and G. muscorum . Only one other species of similar size has been described, Glossogobius minutus , from India with a maximum size known of about 50 mm SL. That species lacks scales in the predorsal region, the pectoral fin base and prepelvic area, similar to the species described here but that species differs in having I,8 anal-fin rays, 18-19 pectoral-fin rays and males with the first one or two dorsal spines filamentous. The dwarf species described here share the following features, which separates them from other species in the genus: mental fraenum indistinct usually with a rounded or truncate posterior margin, rarely with very short lateral lobes fused to the chin ( Fig. 3 ); cheek slightly bulbous, without scales; interorbital narrow, much less than eye diameter; interorbital head pores not paired; predorsal area scaled, naked or with a few scale rows extending to above or just before the posterior preopercular margin ( Fig. 4 ); operculum without scales dorsally; pectoral base naked; prepelvic area usually naked, rarely with a few scattered scales; belly with a large naked patch on midline behind pelvic fin insertion; gill rakers on inner face of first arch and other arches denticulate; typically with two more dorsal rays than anal rays, low pectoral fin count of 13-16, vertebrae 11+15-16 = 26 or 27 and small maximum size of less than 50 mm SL; papilla line 5 very short, extending from below middle of eye to infraorbital pore; a prominent black spot surrounding sixth dorsal spine near base in adults (faint in juveniles). These three species appears to be confined to streams in the Cape York Region of Queensland, and Arnhem Land region of Northern Territory, Australia and southern New Guinea.

Relationships of this group of species are unclear, but the presence of short lateral lobes of the mental fraenum in some large specimens, suggest they may belong to the Glossogobius celebius complex. However, the small mouth and indistinct mental fraenum is also characteristic of the Glossogobius giuris group. Two other small species ( Glossogobius torrentis Hoese & Allen, 1990 and G. coatesi Hoese & Allen, 1990 ) are known from the Sepik and surrounding rivers of northern Papua New Guinea. These species reach a maximum size of 70-100 mm SL and differ from the species treated here in having a prominent curved mental fraenum with distinct lateral lobes, and fully developed papilla lines 5, 7 and 9. Small individuals are often overlooked and assumed to be juveniles. Consequently, it is likely that other dwarf species may exist in other parts of the Indo-Pacific.

The dwarf species treated here were found in some localities with Glossogobius concavifrons and juveniles of that species can be hard to separate from the species treated here. These dwarf species are distinctive from G. concavifrons in usually having 26 or 27 vertebrae (versus usually 28), larger, but few predorsal scales not reaching near the eye in 0-14 rows on the midline (versus reaching to near eye usually with 14-20 scales on the midline), a depressed nape region (versus rounded and elevated); second dorsal rays of I,7-10, rarely I,10 (versus I,9-13, rarely I,9), pectoral rays 13-16, rarely 16 (versus 16-19, rarely 16), longitudinal scale count of 24–28 (versus 29-33). The dwarf species can also be confused with Glossogobius muscorum and G. bellendenensis , which have reduced predorsal scales, similar to the condition in the dwarf species and also reach a similar maximum size (61 mm SL in G. bellendenensis and 44 mm SL for G. muscorum versus 43 mm SL maximum in species described here). The dwarf species described here differ in having fewer vertebrae (26-27 versus usually 28); lower second dorsal rays (I,7-10, rarely 10 versus I,10-11); fewer pectoral fin rays (usually 14-15 versus 16-17) and reduced mental fraenum (usually truncate to a rounded knob versus elevated with distinct lateral lobes).

Figures

Figure 3. – Diagrammatic sketch of mental fraenum. A: Rounded fraenum; B: Truncate fraenum; C: Broad fraenum with short lateral lobes. Scale bar = 5 mm.

Figure 4. – Dark area indicating anterior extent of predorsal and prepelvic scales and head pores in various populations and species of dwarf Glossogobius. A: Glossogobius gnomus; B: G. nanus, Australia; C: G. nanus, Fly River; D: G. pumilus, Bensbach River; E: G. pumilus, Timika region. Scale bar = 5 mm.