Rhinogobius houheensis sp. nov.

(Tables 1–2; Figs. 1–5)

Holotype. BFU 190710001, male, 66.6 mm standard length (SL) (Fig. 1); Baixi River, the upper reach of the Yuan River, Wufeng County, Hubei Province, China, 30°5'6"N 110°40'38"E; collected by Faxiang Hu; July 10, 2019.

Paratypes. BFU 190710002-190710004, 3 females, 60.7–62.4 mm SL, locality same as holotype; July 10, 2019 . BFU 170723001-170723002, 2 females, 61.3–67.9 mm SL; BFU 170723003-170723007, 5 males, 51.1–55.5 mm SL; locality same as holotype; July 23, 2017 . BFU 170723008-170723014, 7 females, 46.2–66.6 mm SL; BFU 170723015, male, 54.2 mm SL; Specific location in 30°4'41"N 110°40'59"E; July 23, 2017. BFU 170725016170725021, 6 females, 51.7–62.4 mm SL; BFU 170725022-170725025, 4 males, 55.5–61.0 mm SL; Specific location in 30°4'4"N 110°41'4"E; July 25, 2017. HNU 170726026-170726027, 2 females, 55.0– 61.2 mm SL; HNU 170726028-170726029, 2 males, 54.0– 69.2 mm SL; Specific location in 30°5'32"N 110°40'15"E; July 26, 2017 . NWIPB 180725030-180725032, 3 females, 62.8–72.5 mm SL; NWIPB 180725033-180725036, 4 males, 42.9–54.2 mm SL; Specific location in 30°5'5"N 110°40'47"E; July 25, 2018 .

Diagnosis. R. houheensis can be distinguished from all its congeners by a combination of the following features: predorsal scale series 0 (Fig. 2); vertebrae counts 12+18=30 (Fig. 3); first dorsal fin rays VI, second dorsal fin rays I/9-I/10 (Fig. 3 and Table 1); pectoral-fin rays 16–17 (Table 1). While alive (Fig. 4), the first dorsal fin consists of dark brown spinous rays and transparent fin membrane, the fin membrane with two navy blue stripes and a black spot between the first to the third spinous rays. The pectoral fin was grayish, its basal portion was light-brown.

Description. Morphometric and meristic measurements for holotype and paratypes given in Table 1.

Body slender, cylindrical anteriorly, laterally and posteriorly compressed. Head moderately broad. Eyes large and dorsolateral in position. Lips thick, with upper lip more prominent than lower one. Snout small, cheek fleshy. Mouth oblique, rear edge extending to vertical line through anterior margin of pupil in males, and merely extend-ing to vertical of anterior edge of orbit in female. Both jaws covered with 3–4 rows of conical and inwardly curved teeth. Anterior nare surrounded by a short tube and posterior nare covered a round hole. Gill opening and extended near-vertical of margin of preopercle.

Fins. First dorsal fin rays VI (Fig. 3 and Table 1); second dorsal fin rays I/9-I/10 (Fig. 3 and Table 1). Second or third spine of first dorsal fin longest and non-filamentous. When depressed, rear tip of first dorsal fin extended to base of second branched ray of second dorsal fin in males, but just reached anterior margin of base of second dorsal fin in female. Anal fin rays I/7-I/8 (Fig. 3 and Table 1). Anal fin origin inserted at vertical line between fourth and fifth branched soft ray of second dorsal fin. Pectoral fin rays 16–17. Pectoral fins broad. Rear tip of pectoral fin extended to vertical line of anus when depressed in male, but could not extend to vertical line of anus in female. Pelvic fin rays I/5, disc rounded, which had two broad membranous lobes (Fig. 1 bottom).

Scales. Body covered with ctenoid scales while mid-trunk scales were enlarged. Anterior predorsal area naked (Fig. 2 and Table 1). Opercle, preopercle, and pelvic base region scale-less. Longitudinal scale series counted 37–40 (modally 38, Table 1). Transverse scale series rounded 12–14 (Table 1).

Head canals. Head canals shown in Figs. 5a and 5b. Nasal extension of anterior oculoscapular canal with terminal pores σ located in vertical between anterior and posterior nares. Anterior interorbital sections of oculoscapular canal separated, with paired pore λ. One single pore κ in posterior region. Pore ω and η present near posterior edge of eyes. Lateral section of anterior oculoscapular canal with pores α and terminal pore ρ. Posterior oculoscapular canal exists two terminal pores θ and τ. Gap between anterior and posterior oculoscapular canals slightly smaller than length of posterior oculoscapular canal. Preopercular canals presented, with pores ε, γ, and δ.

Sensory papillae. Sensory papillae illustrated in Figs. 5b and 5c. Row oblique and uniserial extended under orbit. Row b was longitudinal, extended anteriorly to a vertical through posterior margin of eyes, and its length near orbit diameter. Rows c and d were long, extended to vertical line of rear margin of orbits. Row cp absent. Row f comprised of paired papillae. Opercular papillae included ot, oi, and os. Anterior end of row oi was well-separated from a vertical row ot.

Vertebrae. Total vertebrae counts 12+18=30 (Fig.3, n = 5). In terms of Figs. 3 a–c and 3e (except Fig. 3d, whose body warped and first dorsal fins seem to misregistration while 3D CT scanning), interdigitation of dorsal-fin pterygiophores and neural spines (P–V) 3/II I II I 0/9·10.

Coloration of fresh specimens. Coloration displayed in Fig. 4. Head and body light-brown color with somewhat irregular dark brown spots in both males and females.Color of males deeper compared with that of females. Body dorsal side dark, and ventral side light-dark. Six or seven longitudinal deep brown stripes on lateral. First dorsal fin consisted of dark brown spinous rays and transparent fin membrane, which colored by two navy blue stripes and one black spot from first to third spinous rays; membrane edge covered by golden-yellow speckles. Second dorsal fin membrane also covered golden-yellow spots along edge. Anal fin gray with white margin in both males and females — caudal fin black-brown with a white edge similar to anal fin. Pectoral fin grayish, basal portion light-brown. Pelvic fin membrane grayish.

Distribution and habitat. Currently, the species is only reported from Baixi River (Fig. 6), a freshwater stream in the mountain area, the upper reach of the Yuan River, which is a tributary of the Yangtze River (Fig. 7). It is currently known as an endemic species to this basin, which always lives in shallow part of the river (30–60 cm deep), with sand and gravel mixed substrate. When breeding seasons, the average samples caught by a portable folded fishing net were more in the upper reaches compared with that in the downstream reaches, which implied that to this goby swam the upper reaches of the stream to lay eggs to complete the life histories. Besides, the species had relatively high vertebrae counts. These behaviors suggested that R. houheensis could be a non-diadromous species.

Etymology. The specific name, houheensis, refers to the type locality, the Houhe National Nature Reserve, Hubei Province, China. Chinese name of this species is suggested as ḂOiṘDmñ.

Phylogenetic analysis. The best fit model for the BI tree is GTR + I + G based on AIC. All samples of R. houheensis are clustered into one clade separated from other species of genus Rhinogobius (Fig. 8).

Discussion. The vertebrae count is a substantial diagnostic character of species in genus Rhinogobius (Takahashi & Okazaki 2017) . Suzuki et al. (2017) classified Rhinogobius species as two groups, which had 25–27 vertebrae counts into the lower count group, and vertebrae counts were more than 27 into the higher count group. Comparatively, the vertebrae counts of R. houheensis are almost currently the highest of all species in the genus Rhinogobius, whose number of vertebrae counts is 30.

To distinguish R. houheensis from all its congeners, we compared R. houheensis with 46 valid species with vertebrae counts ≥27 and seven species whose vertebrae counts were unknown (Table 2). Besides vertebrae counts, the other three meristic measurements (predorsal scales, pectoral-fin rays and longitudinal scale counts) were compared. R. houheensis can be distinguished from all its congeners except for R. bedfordi by the following combination of characters: 0 predorsal scales series, 30 vertebrae counts, pectoral fin rays 16–17 and longitudinal scale series 37–40.

Subsequently, R. houheesis was compared with R. bedfordi . Similarly, the longitudinal scales of R. houheesis and R. bedfordi were more than 36. The predorsal scales of R. houheesis were absent, and nape of R. bedfordi covered with small scales. However, R. houheensis could be distinguished from R. bedfordi by having a non-filamentous second spine of the first dorsal fin (vs filamentous in R. bedfordi) (Regan 1908). In addition, R. houheensis is absenting (vs presenting in R. bedfordi) (Suzuki et al. 2017) vertical dark lines or rows of dark spots on the caudal fin.

The maximum vertebrae counts in the genus Rhinogobius were reported to be 29 (Suzuki et al. 2017; Takahashi & Okazaki 2017; Chen et al. 2008; Endruweit 2018).However, some original descriptions of vertebrae counts of the Rhinogobius species did not consider the last caudal vertebrae (urostyle). Therefore, we further compared R. houheensis with R. carpenter, R. liui, R. multimaculatus, R. ngutinhoceps and R. phuongae, which have 29 vertebrae counts. Except for vertebrae counts, R. houheensis could be distinguished from R. carpenter, R. ngutinhoceps and R. phuongae by the following character: 0 predorsal scales series (Table 2). The descriptions (Wu et al. 2008) of R. liui and R. multimaculatus confirmed that the vertebrae counts did include the last caudal vertebrae (urostyle). Conclusively, the new species that the current study described could also be differentiated from species of Rhinogobius whose vertebrae counts were 29.

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a Nape covered with small scales.

b 0 in males, 2–4 in females.

The strongly supported monophyly of R. houheesis population according to Cyt b datasets (Fig. 8) also support-ed the reliability of our results. Those Cyt b datasets of R. houheesis would contribute to the phylogenetic analyses of Rhinogobius species in the future study.

The vertebrae counts were potentially related to the four ecotypes of Rhinogobius (Akihito et al. 2000) . In the rivers and streams of the continents, the species of Rhinogobius generally have high vertebrae counts (Chen et al. 2008). R. houheensis would be a typical sample to study the relationship between morphology and phylogeny, as well as the mechanism of this environmental adaptability in the future study.