Rhinogobius Gill, 1859

SUƶU, Toshiyuki & Kƚ, Seishi, 2019, Two New Lentic, Dwarf Species of Rhinogobius Gill, 1859 (Gobiidae) from Japan, Bulletin of the Kanagawa Prefectural Museum (Natural Science) 48, pp. 21-36 : 22-23

Genus Rhinogobius Gill, 1859

Rhinogobius Gill, 1859: 145 (type species: Rhinogobius similis Gill, 1859 by original designation and monotypy).

Tu k u g o b i u s Herre, 1927: 119 (type species: Rhinogobius carpenteri Seale, 1910 by original designation).

Sinogobius Liu, 1940: 215 [type species: Gobius (S i n o g o b i u s) s z e c h u a n e n s i s Liu, 1940 (= Rhinogobius liui Chen & Wu, 2008 ) by original designation and monotypy].

Pseudorhinogobius Zhong & Wu, 1998: 149 (type species: Pseudorhinogobius aporus Zhong & Wu 1998 by original designation and monotypy).

Diagnosis. Rhinogobius belongs to the gobiid subfamily Gobionellinae (sensu Pezold, 1993, 2011), and is distinguished from the other gobionelline genera by the following combination of characters ( Chen & Shao, 1996; Yang et al., 2008; Suzuki et al., 2015, 2017): first dorsal fin with 5–7 spines; second dorsal fin with a single spine and 6–11 segmented rays; anal fin with a single spine and 5–11 segmented rays; pectoral fin with 14–23 segmented rays; pelvic fin with a single spine and five segmented rays; 25–44 longitudinal scales; 7–16 transverse scales; P-V 3/2211 0/9 or, in a few exceptions, its derived pattern; 10– 11+15–18=25–29 vertebrae; snout, cheek and operculum naked; body largely with ctenoid scales; cheek with a longitudinal pattern of sensory papillae (sensu Hoese, 1983), except for a single species, R. similis , having several short transverse rows of sensory papillae below the eye; gill opening moderate in size, its anteroventral end extending to a vertical through posterior margin of preopercle; pelvic fins fused medially into a circular/ ovoid disc via frenum (between spines) and connecting membrane (between innermost rays).

Remarks. Rhinogobius is currently known as the most species-rich freshwater gobiid genus, comprising 83 valid species (Suzuki et al., 2017; Takahashi & Okazaki, 2017; Endruweit, 2018; Li et al., 2018; Wu et al., 2018; Xia et al., 2018; present study). As indicated by Chen & Shao (1996) and Suzuki et al. (2015), the genus is divided into two distinct groups; one comprises only a single species R. similis , whereas the other includes all the remaining species. Rhinogobius similis differs from the other congeners by having large ctenoid scales on the nape (vs. nape naked or with cycloid scales in the others) and several short transverse rows of sensory papillae on the cheek (vs. no distinct transverse rows of sensory papillae on cheek). We here assign all species of the genus but R. similis to the “ Rhinogobius brunneus complex”, following Chen & Shao (1996).

Endruweit (2017) resurrected Tukugobius Herre, 1927 , previously regarded as a junior synonym of Rhinogobius , as valid; assigning three described species known from the Philippines, Tukugobius bucculentus Herre, 1927 , Rhinogobius carpenteri Seale, 1910 (type species of Tukugobius ), and Tukugobius philippinus Herre, 1927 , to Tukugobius , with all others to Rhinogobius . However, on the basis of the following reasons, we do not concur with his conclusion. First of all, it is too early to resurrect Tukugobius as valid, based on these three species. Like R. carpenteri , the type specimens of T. bucculentus and T. philippinus were destroyed during the Second World War ( Eschmeyer, 1998; Kottelat, 2013), and the taxonomic status of these species is open to debate. For these two species, Endruweit (2017) merely examined the non-type specimens from the Philippines and did not state the reasons why these were congeneric with R. carpenteri , only stating, “ Tukugobius carpenteri is readily distinguished from all species currently allocated in Rhinogobius by seven pterygiophores supporting the first dorsal fin (vs. 6 in all species from continental Asia, Japan, Taiwan, and Hainan), the first pterygiophore of second dorsal fin inserted in interneural space 9 (vs. 8)”, These characters need further investigation based on broader sampling. For example, some specimens of Rhinogobius sp. BF (one of the new species described below) and Rhinogobius sp. BB have seven pterygiophores for the first dorsal fin, and R. fluminues , and some specimens of Rhinogobius sp. YB have the first pterygiophore of second dorsal fin inserting behind neural spine of ninth vertebra (TS, personal investigation). These inter- or intra-specific variations suggest that the characters shown by Endruweit (2017) are not sufficient to distinguish Tukugobius from Rhinogobius . Furthermore, Endruweit (2017) indicated that some differentiations between R. carpenteri (type species of Tukugobius ) and R. similis (type species of Rhinogobius ), such as configuration of sensory-papillae rows on the cheek (i.e., transverse rows absent vs. present) and squamation of pectoral-fin base (i.e., naked vs. scaly), “may possess intrinsic value at generic level.” Nevertheless, in the gobioid fishes, more than a few examples are known to have these characters as intrageneric variations (see, e.g., Akihito et al., 2013). And, as noted above, the presence of the transverse rows of sensory papillae does not only distinguish R. similis from Tukugobius , but also from the other species of Rhinogobius ; if following his scenario, we should split further his Rhinogobius into two genera. It appears to be merely artificial, less-necessary splitting. We, therefore, do not accept his idea on the limits of Rhinogobius / Tukugobius , and, in this paper, regard the latter ( Tukugobius ) as a junior synonym of the former ( Rhinogobius ).