Rhinogobius telma, SUƶU & Kƚ, 2019

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 : 28-32

Rhinogobius telma sp. nov.

(Standard Japanese name: Tokai-yoshinobori)

( Table 1 ; Figs. 4–6 )

Rhinogobius sp. TO: Suzuki & Sakamoto, 2005: 13 (Gifu and Aichi prefectures, Japan); Suzuki et al., 2010: 11 (Gifu and Aichi prefectures, Japan); Akihito et al., 2013: 1459 (Shizuoka, Aichi, Gifu, Mie prefectures, Japan).

Holotype. BLIP 20000268 , male, 28.7 mm SL, Tokigawa River , Izumichouotomi, Toki, Gifu Prefecture, Japan, 35°21'33.9"N 137°11'27.4"E, 1 April 2000.

Paratypes. Total 13 specimens (ten males and three females), 28.8–39.5 mm SL: BLIP 20000256–20000262 , 20000264–20000266 , seven males and three females, 28.8–37.8 mm SL, Pond of Yanagase park, Yahagi-gawa River, Toyoda, Aichi Prefecture, Japan, 34°59'43.1"N 137°08'51.3"E, 1 April 2000 ; BLIP 20000400 , male, 30.7 mm SL, Shin-ike Pond , Yawatacho, Toyokawa, Aichi Prefecture, Japan, 6 April 2001 ; BLIP 20010401 , male, 33.0 mm SL, Ibi-gawa River , Naoecho, Ogaki, Gifu Prefecture, Japan, 35°20'46.9"N 136°39'19.1"E, 13 November 2001 ; OMNH-P 43682 , male, 39.5 mm SL, a cleared and stained, 2000.04.01 , collected with the holotype.

Diagnosis. Rhinogobius telma is distinguished from all congeneric species by the following unique combination of features: scales on predorsal area small cycloid, 3–15 predorsal scales on predorsal midline; 10+16=26 vertebrae; a low first dorsal fin in males, not extending posteriorly to origin of second dorsal fin when adpressed; third spine of first dorsal fin longest; the lateral and ventral sides of belly with ctenoid and small cycloid scales, respectively; posterior oculoscapular canal and preopercular canal absent; sensory-papillae rows on cheek arranged longitudinally, with no transverse rows; first dorsal fin with a single longitudinal row of vertically-elongate dark markings; no dark large circle or quadrangle markings (spots or blotches) at anteriorpart of first dorsal fin; lower half of caudal fin without reddish orange coloration; caudal fin with some vertical rows of dark dots in both sexes.

Description. Dorsal-fin rays VI-I, 8* (14); anal-fin rays I, 8 (3) or I, 9* (11); pectoral-fin rays 19 (3), 20* (6), or 21 (5); pelvic-fin rays I, 5* (14); segmented caudal-fin rays 9+7 (1), or 9+8* (13); branched caudal-fin rays 6+6* (2), 7+6 (5), or 7+7 (7); longitudinal scales 31 (3), 32 (2), 33* (7), or 34 (2); transverse scales 9* (8), or 10 (6); scales between origin of dorsal fin and dorsal insertion of pectoral fin 6 (3), or 7* (11); predorsal scales 3*(1), 4 (2), 6 (1), 8 (1), 11 (3), 12 (2), 13 (1), 14 (2), or 15 (1); P-V 3/22110/9* (13); vertebrae 10+16=26* (13).

Proportional measurements based on holotype and three paratypes ( BLIP 20000256, 20000265, 20000269) are given in Table 1 . Body relatively short and small (reaching up to 40 mm SL), slightly compressed anteriorly, compressed posteriorly. Head moderately large, slightly depressed. Snout short and round. Eye large, located dorsolaterally on head at a vertical through midpoint between snout tip and posterior margin of preopercle. Cheek somewhat fleshy. Lips thick and fleshy; lower lip slightly protruding beyond upper lip; gape oblique, forming an angle of about 35–40 (35 in holotype) and 40–50 degrees with body axis in males and females, respectively; posterior margin of lower jaw extending slightly beyond a vertical through anterior margin of eye. Anterior naris a short tube without skin flap at its tip, located slightly behind midpoint between snout tip and anterior margin of eye; posterior naris a round pore with low rim, closer to eye than to anterior naris. Gill opening extending anteriorly to a vertical through posterior margin of preopercle. Gill membranes broadly attached to isthmus. No fleshy papillae- or finger-like projections on lateral margin of shoulder girdle. Tongue free from floor of mouth, with rounded anterior margin. Genital papillae cone-shaped in males and oval in females.

Origin of first dorsal fin slightly behind a vertical through dorsal insertion of pectoral fin; first dorsal fin trapezoid or “shogi-piece” shaped in males (“shogi-piece” shaped in holotype), usually semicircular in females; third spine longest; all dorsal-fin spines slender and flexible, not filamentous; when adpressed, third-spine tip not extending to origin of second dorsal fin in both sexes; when adpressed, posterior end (distal tip of the sixth spine) of first dorsal fin extending slightly behind origin of second dorsal fin in males, but not extending to it in females. Second dorsal fin separated from first dorsal fin; second dorsal fin higher than first dorsal fin in height in both sexes; all segmented dorsal-fin rays branched; seventh branched ray longest in males, whereas second ray longest in females; when adpressed, posterior end of second dorsal fin not extending to procurrent-rays part of caudal fin; posterior end of base of second dorsal fin above posterior end of anal-fin base. Origin of anal fin below base of first, second or third (second in holotype) branched second dorsal-fin ray; anal fin slightly lower than second dorsal fin in height; all segmented anal-fin rays branched; sixth or seventh branched ray longest in males (seventh in holotype), whereas fourth ray longest in females; when adpressed, posterior end of anal fin not extending to procurrent-ray of caudal fin. Caudal fin nearly rounded. Pectoral fin oval, posteriorly extending around a vertical thorough origin of second dorsal fin (not reaching in holotype) in both sexes; pectoral-fin rays branched, except for dorsalmost and ventralmost rays fin usually unbranched (unbranched in holotype). Pelvic fins fused medially by well-developed frenum (between spines) and connecting membrane (between innermost rays), forming a round cup in males and a longitudinally elongate cup in females; pelvic fins extending posteriorly to a vertical through fifth or sixth spine base of first dorsal fin (fifth in holotype), and not reaching to anus; pelvic-fin spine without membranous lobe at its tip; all pelvic-fin segmented rays branched; first branched ray longer than spine; first branch of fifth pelvic-fin ray bifid ( Fig. 4A ).

Scales on body small ctenoid anteriorly, moderately large ctenoid posteriorly. Scaly area on body extending posteriorly to base of caudal fin; basal part of caudal fin with small cycloid scales. Anterodorsal part of body before a diagonal line from middle of first dorsal-fin base to dorsal insertion of pectoral-fin with small scales. Anterior part of predorsal area naked. Predorsal squamation with trifurcate anterior edge, anterior extension of middle and both sides extending anteriorly beyond a transverse line through dorsalmost point of pectoral-fin axil to above through middle of opercle ( Fig. 4B ). The other part of head naked. Lateral and ventral sides of belly with ctenoid and small cycloid scales, respectively. Pelvic-fin axil naked. Scaly area of belly usually extending anteriorly to pelvic-fin insertion. Base of pectoral fin and prepelvic areas usually with some small cycloid scales (0–4 in preventral midline).

Cephalic sensory systems of BLIP 20000264 are illustrated in Suzuki & Sakamoto (2005: 15, fig. 1), and not repeated here. Based on our examination of 13 specimens (BLIP 20000256–20000262, 20000264–20000266, 20000268, 20010400, 20010401), considerable variations in development of sensory canals on head are found. On the anterior oculoscapular canal, eight specimens including holotype have a nasal extension with terminal pore B' located anterodorsal to posterior naris; anterior interorbital sections separated with two paired pores C and D; pore E and terminal pore F' behind posterior edge of eye; lateral section lacking. Two specimens have the anterior interorbital sections separated with a single median pore D; other pores same as holotype. Three specimens with an additional pore between C and D, or between D and E; other pores same as holotype. All specimens including holotype have no posterior oculoscapular canal and preopercular canal. The following description of sensory papillae is based on BLIP 20000264. Sensory-papillae row a oblique and uniserial, composed of five sparsely arranged papillae, extending anteriorly to a vertical through middle of eye. Row b longitudinal, composed of densely arranged papillae, extending anteriorly to a vertical through posterior margin of eye; its length slightly shorter than eye diameter. Row c composed of sparsely arranged papillae, extending posteriorly slightly behind a vertical through posterior margin of eye. Row d composed of densely arranged papillae, extending posteriorly slightly behind a vertical through posterior margin of eye. Rows cp and f comprising single and a pair of papillae, respectively. Anterior end of row oi well separated from a vertical row ot.

Coloration of males (see also Suzuki & Sakamoto, 2005: 16, figs. 2A). Freshly-collected coloration of male holotype ( Fig. 5A ) is as follows. Ground color of head and body yellowish gray. Iris vivid yellow, margined dorsally by vivid green. Two oblique stripes on snout; one dull red between eye and tip of snout, the other broad green between ventral margin of eye and posterior end of upper jaw. Cheek grayish. Dorsal parts of cheek and operculum, nape and occipital region with several irregular-shaped, short dull orange lines or spots. Ventroanterior part of head purplish blue. Branchiostegal membrane reddish yellow, without any distinct markings. Dorsal part of operculum with a purplish blue longitudinal marking. Base of pectoral fin with a large oblong black marking. Dorsum of body with six saddle-like, large grayish brown blotches; anteriormost one below origin of first dorsal fin, second one below base of first dorsal fin, third one below between first and second dorsal fins, fourth one below base of second dorsal fin, and the last two on caudal peduncle. Midlateral body with a longitudinal series of five rectangular, large grayish brown blotches; each midlateral blotch below interspace between saddle-like blotches of dorsum of body; interspaces between grayish brown blotches on midlateral body pale green. Belly whitish, tinged with yellow dorsally. Dorsal fins gray, rays yellowish with pale yellow dorsal margins; first dorsal fin with a row of narrow, transversely-elongate violet blotches along spines; lower half of second dorsal fin with 2–3 longitudinal rows of dull purplish red dots. Anal fin light yellowish orange, with a narrow white lower margin. Caudal fin gray, rays yellowish with pale-yellow posterior margin; ventral part of caudal-fin base with two black blotches; central part of caudal fin with two or three vertical rows of gray dots. Pectoral fin nearly transparent, whitish basally, with yellowish gray rays. Pelvic fins gray. When preserved in alcohol ( Fig. 5B ), all blue, green, orange, purple, red and yellow markings faded; ground color of head and body turns to yellowish white; blackish markings on body turn to brown.

Coloration of female ( Fig. 6A ; Suzuki and Sakamoto, 2005: 16, fig. 2B). Freshly-collected coloration of female resembles that of male, except as follows. Cheek not grayish. Branchiostegal membrane not yellowish. An oblong black marking at base of pectoral fin smaller than male’s marking. First two large grayish brown blotches of midlateral body connected. Caudal-fin base with a “<” sharped grayish brown blotch. Pelvic fin grayish white. When preserved in alcohol ( Fig. 6B ), all blue, green, orange, purple, red and yellow markings faded; ground color of head and body turns to yellowish white; blackish markings on body turn to brown.

Coloration when alive (based on photographs in Matsuzawa, 2011). Coloration in males when alive in aquaria resembles that of freshly-collected specimens, except as follows: ground color of head and body yellowish gray; first dorsal fin black, with reddish yellow dorsal margin; markings of second dorsal fin and caudal fins grayish brown.

Distribution. Rhinogobius telma is hitherto known only from the Tokai District of temperate Japan (viz., Aichi, Mie, Gifu, and Shizuoka prefectures), although the population in Shizuoka Prefecture seems to have been artificially introduced ( Suzuki & Sakamoto, 2005; Suzuki et al., 2010; Akihito et al., 2013).

Habitat. Rhinogobius telma is found in shallow freshwater areas with mud bottoms and aquatic vegetation, such as ponds, marshes, reservoirs, canals, creeks of middle or lower reaches of rivers (Suzuki & Mukai, 2010; present study). It is a non-diadromous species, restrictedly found in non- or slow-flowing freshwater habitats throughout the life cycle ( Tsunagawa et al., 2010b; present study).

Remarks. Rhinogobius telma was first noticed by Takahashi et al. (1998); they reported a putative unnamed species of the genus, which agrees well with R. telma in morphological characters, from Aichi Prefecture, Japan, in the 31st annual meeting of the Ichthyological Society of Japan. Subsequently Akihito et al. (2000) provisionally regarded it as one of the varieties of the “Shimahiregata” morphotype of their Rhinogobius sp. OR that further morphological/molecular analyses towards our better understanding for these varieties is necessary. On the internet website (https://tansuigyo.net), anonymous proposed a nickname “Ushi-yoshinobori” for the goby, probably identical with R. telma herein described, in order to distinguished it from the congeners in the Japanese waters. The page is not dated; according to the website writer(s), the page was originally launched on 11 November 2000, but the contents appear to have been modified after that; at least now, many photographs of live fish of the species in aquaria are shown there (downloaded on 17 September 2018). Suzuki & Sakamoto (2005) reported information about the morphology, distribution and habitats of R. telma (as an undescribed species) in detail, and proposed a new standard Japanese name “Tokai-yoshinobori” with a specific abbreviation “TO” for distinguishing it from the other undescribed congeners (viz., “ Rhinogobius sp. TO”) on the basis of a specimen ( BLIP 20000256), that is designated here as a paratype of R. telma .

Yamazaki et al. (2015) analyzed nuclear DNA of the Japanese species of Rhinogobius and concluded that R. telma (as an undescribed species) has a sister relationship with R. flumineus . The latter ( R. flumineus ) is only a single species of the Group I (described below) in the Japanese waters; this is one of the reasons why we recognize the subgroups of the R. brunneus complex assembled based on the vertebral counts (i.e., the Group I and Group II: described below) as the grades (not the clades).

Etymology. The specific name “ telma ” is derived from the Greek word meaning standing water or marsh, in reference to typical habitat of the species. The name should be treated as a noun in apposition.

Figures

Fig. 4. Ventral view of pelvic fin (A) and dorsal view of head (B) of Rhinogobius telma (OMNH-P 43682, paratype, male, 39.5 mm SL), stained with Alizarin Reds. White line indicates the first segment of each branch in the fifth soft ray. Black arrow indicates a slit between branches. Pink dots indicate scales along edge of scaly area on nape and occipital region; P1, P2, and P3 indicate boundary of anterior extension of scaly area along predorsal midline, boundary of anterior extension of scaly area on side of occipital region, and boundary of most concave point of scaly area between P1 and P2, respectively.

Fig. 5. Freshly-collected (A) and alcohol preserved (B) holotype of Rhinogobius telma (BLIP 20000268, male, 28.7 mm SL). Photographed by T. Suzuki.

Fig. 6. Freshly-collected (A) and alcohol preserved (B) paratype of Rhinogobius telma (BLIP 20000265, female, 31.1 mm SL). Photographed by T.Suzuki.