Rhinogobius aonumai aonumai, Suzuki & Oseko & Yamasaki & Kimura & Shibukawa, 2022

Suzuki, Toshiyuki, Oseko, Naoharu, Yamasaki, Yo Y., Kimura, Seishi & Shibukawa, Koichi, 2022, A New Species with Two New Subspecies of Rhinogobius (Teleostei: Gobiidae) from Yaeyama Group, the Ryukyu Islands, Japan, Bulletin of the Kanagawa Prefectural Museum (Natural Science) 51, pp. 9-34 : 13-20

Rhinogobius aonumai aonumai subsp. nov.

(New Standard Japanese name: Iriomote-painukibara-yoshinobori)

( Figs. 1–8 & 17A; Tables 1 & 3)

Rhinogobius brunneus (not of Temminck & Schlegel): Hayashi, 1984: 259 (in part: Medium Egg Type, Iriomote-jima Island , the Yaeyama Group of the Ryukyu Islands, Japan) .

Rhinogobius sp. YB: Iwata, 1989: 598 (in part: Iriomote-jima Island); Akihito et al., 1993: 1082 (in part: Iriomote-jima Island); Akihito et al., 2000: 1255 (in part: Iriomote-jima Island); Akihito et al., 2002: 1255 (in part: Iriomote-jima Island); Suzuki et al., 2004: 460 (in part: Iriomote-jima Island); Akihito et al., 2013: 1461 (in part: Iriomote-jima Island); Suzuki et al., 2021: 466 (in part: Iriomote-jima Island).

Holotype. As for Rhinogobius aonumai sp. nov.

Paratypes. As for Rhinogobius aonumai sp. nov.

Photograph Records from Image Database of Fishes. Arabara-gawa River : KPM-NR 211716–211721, 3 males and 3 females, 28.0–43.0 mm SL, 24°22'14.43"N 123°45' 47.16"E, 118 m above sea level, 18 February 2013, Yo Y. Yamasaki; Hora-gawa River: KPM-NR 211722– 211733, 4 males and 8 females, about 40–55 mm SL, upper reaches above Hora Fall (total vertical height 23.3 m), 24°22'10.71"N 123°54' 3.61"E, 174 m above sea

level, 12 June 2011, Yuichi Kano ; Namure-gawa River , a tributary of the Nakama-gawa River System : KPM-NR 211734–211738, 3 males and 2 females, about 40 mm SL, 24°17'50.7"N 123°49' 43.4"E, 15 m above sea level, 15 March 2020, Yoshiyuki Akatuka; Nishifunatsuki-gawa River , a tributary of the Nakama-gawa River System: KPM-NR 211739 and 211740, male and female, about 40 mm SL, 24°18'33.9"N 123°51' 31.0"E, 87 m above sea level, 27 June 2020, Yoshiyuki Akatuka .

Diagnosis. Rhinogobius aonumai aonumai is distinguished from all congeneric species-group taxa (species and subspecies) by having the following combination of features: 9–15 predorsal scales; 32–37 longitudinal scales; 11+15–17=26–28 vertebrae, mode 27; anteriormost two pterygiophores (proximal radials) of second dorsal fin mounted over neural spine of tenth (sometimes nineth and tenth) vertebra; fifth segmented pelvic-fin ray divided into 3–4 (usually four) branches at the position where proximal most segment of each branch alignes transversely; sensory-papillae rows on cheek arranged longitudinally, with no transverse rows; yellow-colored body in freshly-collected; no dark spot on first dorsal fin; caudal fin with 4–14 and 3–10 vertical rows of dark spots or forming dark zigzag bands in males and females, respectively; a pair of short, vertically aligned, rod-shaped dark mark on caudal-fin base in females.

Description. First dorsal-fin rays V (2), VI *(25) or VII (2); second dorsal-fin rays I, 7* (1), I, 8 (21) or I, 9 (7); anal-fin rays I, 8* (21) or I, 9 (8); pectoral-fin rays (left/ right) 18/19 (2), 19/18 (1), 19/19 (16), 20/19 (2) or 20/20* (7); pelvic-fin rays I, 5 (28); segmented caudal-fin rays (upper part + lower part) 8+8 (1) or 9+8* (27); branched caudal-fin rays (upper part + lower part) 6+6 (1), 7+7* (15), 7+8 (2), 8+7 (5), 8+8 (4) or 9+8 (1); longitudinal scales 32 (1), 33 (6), 34 (7), 35 (6), 36* (7) or 37 (1); transverse scales 9 (4), 10 (12), 11 (8) or 12* (3); scales between origin of dorsal fin and dorsal insertion of pectoral fin 7 (8), 8 (9), 9* (9), or 10 (2); predorsal scales 9 (2), 10 (3), 11* (9), 12 (5), 13(5), 14(3) or 15 (1); number of the first branches of fifth segmented pelvic-fin ray (left/ right) at the position where proximal most segment of each branch alignes transversely ( Fig. 3A) 3/3 (7), 3/4 (1), 4/3 (2) or 4/4* (18); P-V 3/122000/10 (1), 3/122100/10 (1), 3/122110/10 (1), 3/122111/10(1), 3/21210/9&10 (3), 3/212100/10 (1), 3/212101/10 (1), 3/212110/10 (1), 3/221010/10 (1), 3/22110/9&10* (3) or 3/221100/10 (8); vertebrae (abdominal + caudal = total vertebrae) 11+15=26 (1), 11+16=27* (18) or 11+17=28 (2).

Head slightly large and slightly depressed; body slightly slender, slightly compressed anteriorly, and compressed posteriorly (see “Variations between rivers”). Snout nearly pointed, long and longer than eye diameter; snout length of males greater than that of females. Eye large, dorsolateral on head, and located slightly behind a vertical through midpoint between snout tip and posterior margin of preopercle. Cheek somewhat bulbous and fleshy. Lips thick and fleshy; anterior tips of both lips even or usually lower lip slightly protruding anteriorly*; gape slightly oblique; posterior margin of lower jaw extending posteriorly to a vertical through anterior margin of eye in females and slightly beyond it* in males. Anterior naris a short tube without skin flap at its tip, and its base located slightly behind the midpoint between snout tip and anterior margin of eye. Posterior naris a round pore with low rim and located at the midpoint between base of anterior naris and anterior margin of eye. 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 about an eye diameter behind a vertical through dorsal insertion of pectoral-fin; first dorsal fin in males near falcate shape, pentagon (becoming slightly narrower distally) shape or semioval*, and higher than second dorsal fin, whereas, in females, semicircular or semioval, and slightly higher than, or slightly lower than second dorsal fin in height; usually second, or third* spine longest; all dorsal-fin spines slender and flexible; usually not filamentous*, or distal tip of second or third spine slightly filamentous; posterior tip (= distal tip of second, usually third, or fourth* spines) of first dorsal fin in males extending between front of origin* and base of third segmented ray of second dorsal fin when adpressed, whereas, in females, posterior tip (= distal tip of third, fourth, fifth or usually sixth spines) not extending to origin of second dorsal fin when adpressed. First and second dorsal fins not connected by membrane (see “Variations between rivers”); all segmented rays of second dorsal fin branched; seventh* or eighth, and second, fourth or sixth segmented rays longest in males and females, respectively; posterior tip (= distal tip of last* or penultimate segmented ray) of second dorsal fin usually not extending* to caudal fin, or to it when adpressed; posterior end of second dorsal-fin above posterior end of anal-fin base. Origin of anal fin below between bases of first and second segmented rays of second dorsal fin; anal fin equal to*, or usually slightly lower than second dorsal fin in height; all segmented anal-fin rays branched; fifth, sixth or seventh* and fourth or sixth segmented rays longest in males and females, respectively; posterior tip (= distal tip of last or penultimate* segmented ray) of anal fin not extending to caudal fin when adpressed. Pectoral fin oval, extending posteriorly to a vertical between base of sixth spine and posterior end of base* of first dorsal fin; all pectoral-fin rays branched, except for dorsalmost ray usually not branched (left side*), or branched once (right side*); ventralmost ray not branched (both side*), or branched once. Pelvic fins fused medially by well-developed frenum (between spines) and connecting membrane (between innermost rays), forming a circular cup-like disc; pelvic fins extending posteriorly to a vertical between bases of second and fifth spines of first dorsal fin (base of third spine*) (see “Variations between rivers”); pelvic fins not reaching to anus; pelvic-fin spine with a rounded membranous lobe at its tip; all segmented rays of pelvic fin branched. Caudal fin elliptical or fan-shaped*.

Scales on body largely ctenoid, becoming smaller anteriorly; anterior edge of scaled areas with ctenoid scales on lateral, dorsal and ventral sides of body reaching respectively to a vertical between a little behind pectoral-fin axilla and origin of second dorsal fin, to second dorsal-fin base, and to anal-fin base (see “Variations between rivers”; Figs. 4A, 4C). Small cycloid scales on anterodorsal part of body before the area with ctenoid scales. Predorsal squamation with trifurcate anterior edge; its mid-anterior extension ( Fig. 3B: P1) extending anteriorly to between transverse lines through sensory-canal pores H′ and L′; anterior extensions of lateral sides ( Fig. 3B: P2) extending anteriorly to posterior oculoscapular canal; greatest concaved point of anterior margin of scaled area of predorsal region between P1 and P2 ( Fig. 3B: P3) extending posteriorly to above between sensory-canal pore H′ and upper end of pectoral-fin axilla. Pectoral-fin base usually naked, or with one or two small cycloid scales. Prepelvic area usually naked, or with some small cycloid scales. Scaled area on belly with small cycloid scales usually extending anteriorly to, or not, side of prepelvic area; belly above pelvic fin naked, and its following anterior part of ventral midline of belly usually naked, or with some small cycloid scales (see “Variations between rivers”; Figs. 4B, 4D).

Cephalic sensory systems are illustrated in Fig. 5. Nasal extension of anterior oculoscapular canal with terminal pore B′ located above both nares. Anterior interorbital sections of the anterior oculoscapular canal separated bilaterally, with paired pore C and a single pore D. Pore E present just behind posterior edge of eye. Lateral section of anterior oculoscapular canal with anterior pore F and terminal pore H′. Posterior oculoscapular canal with two terminal pores K′ and L′. A gap between anterior and posterior oculoscapular canals much narrower than the length of the posterior oculoscapular canal. Preopercular canal present, with three pores M′, N, and O′. In the three paratypes, there is an accessory pore on the canal between pores C and D, pores D and E, and pores M′ and N. Sensory-papillae row “a” oblique and uniserial, composed of loosely-arranged papillae, and extending anteriorly to a vertical through midpoint between anterior margin of eye and anterior margin of pupil. Row “b” longitudinal, composed of densely-arranged papillae, extending anteriorly to a vertical through the center of pupil, and longer than eye diameter in length. Row “c” composed of loosely-arranged papillae, extending posteriorly to a vertical through posterior margin of the eye. Row “d” composed of densely-arranged papillae, extending posteriorly to a vertical through posterior margin of the pupil. Row “cp” comprising a single papilla. Row “f” comprising paired papillae.Anterior end of row “oi” a little separated from a vertical row “ot”.

Coloration of male when freshly collected ( Figs. 1A, 1B, 6A, 6C, 6E, 6G, 6I, 7A, 7C, 7E, 7G). Ground color of head and body usually reddish yellow. Belly pale yellow, and its side greenish. Head grayish; cheek, operculum and gill membrane usually with densely-arranged, many small reddish orange dots (see “Variations between rivers”). Snout with a broad oblique reddish orange stripe between anterior margin of eye and anteriormost part of snout. Several irregular-shaped, short reddish orange stripes and minute spots on dorsal surface of snout and interorbital space, occipital region and nape; anterodorsal margin of cheek with a narrow reddish orange line edged ventrally by a bluish green line; temporal region above operculum with usually a short reddish orange stripe*, or dashed line; upper part of operculum with usually an oblique reddish orange stripe, or dashed line*. Almost all scale pockets on body with reddish orange spots. Ground color of fin membranes pale yellow, partially with bluish sheen. Spines and segmented rays gray. Anterodorsal part of first dorsal fin and distal margin of second dorsal bright yellow; distal margin of anal fin white; distal margin of caudal fin usually bright yellow, or ventral margin white*; membranes around spines and segmented rays of first dorsal and anal fins, and upper and lower parts of caudal fin reddish orange. Second dorsal fin with usually 1–6 (5*) longitudinal rows of reddish orange spots* or forming zigzag stripes; indistinct pale orange mottles above these spots or stripes. Central part of caudal fin with usually 4–14 (13*) vertical rows of reddish orange* or pale orange spots, or forming zigzag bands. Pectoral-fin base with a distinct reddish orange bow-shaped mark, and one or two* vertical rows of reddish orange spots behind it.

Coloration of female when freshly collected ( Figs. 2A, 2B, 6B, 6D, 6F, 6H, 6J, 7B, 7D, 7F, 7H). Resembles that of male, except as follows. Orange marks of head and body darker. Orange dots on cheek fewer in number; on operculum fewer in number or absent; gill membranes with no orange dots. Ventral side of body usually with no orange dots. Spines and segmented rays of fins except for those of first dorsal and pelvic fins yellowish. Second dorsal fin with 3–5 longitudinal rows of reddish orange spots or forming zigzag stripes; membrane above these spots or stripes pale pink. Caudal-fin base with a pair of short, vertically aligned, rod-shaped deep reddish orange mark; central part of caudal fin with 3–10 vertical rows of pale pink spots or forming zigzag bands, membrane behind these spots or bands usually pale pink, or forming indistinct mottles. Pectoral-fin base with a deep reddish orange band or a vertical row of or reddish orange spots behind a bow-shaped mark.

Coloration when alive based on underwater photographs ( Fig. 8). Coloration when alive in the populations of Hinai-gawa and Urauchi-gawa rivers in Iriomote-jima Island resembles that of freshly-collected coloration, except as follows. In the population of Hinai-gawa River, ground color of head and body light grayish green; belly bright yellow. In the population of Urauchi-gawa River, head and body greenish; belly bright yellow; orange and pink color darker; anterodorsal part of first dorsal fin and distal margin of second dorsal fin bright greenish in males.

Coloration when preserved in alcohol ( Figs. 1C, 2C). Ground color of head and body turned to yellowish gray; blue, green, pink, yellow and white color faded; orange and red color turns to brown or gray. Upper half of body with 1–2, and 3–4 longitudinal row(s) of brown spots in males and females, respectively.

Variations between rivers. In females of the population of Hinai-gawa River, head length is shorter [28.1–28.9 % in SL (average 28.6 %) vs 29.0–31.6 % (average 30.8 %) than those of the other populations]; head, body, and caudal peduncle are lower in depth [head depth 14.2–14.8 % (average 14.5 %) vs 16.4–18.7 % (average 17.5 %), body depth at origin of pelvic-fin 14.2–14.8% (average 14.5 %) vs 16.4–18.7 % (average 17.6 %), caudal peduncle depth 11.0–11.4 % (average 11.2 %) vs 10.7–12.8 % (average 12.2 %)]; interspace between dorsal fins longer [8.2–8.6 % (average 8.5 %) vs 4.9–8.1 % (average 6.5 %)] than females of the other populations.

In the population of Hinai-gawa River, pelvic fins are shorter, extending usually posteriorly to a vertical between bases of the second and third spines of the first dorsal fin, whereas the fins extend posteriorly to a vertical between bases of the third and fifth spines of the first dorsal fin in the other populations. In the populations of Kuira-gawa and Aira-gawa rivers, anterior margin of the ctenoid scale area extends to a little behind pectoral-fin axilla ( Fig 4A), whereas the area extends to a vertical between origins of first and second dorsal fins in the other population ( Fig. 4C); ventral midline of belly largely covered with small cycloid scales ( Fig. 4D), although naked except posterior part in other populations ( Fig. 4B).

Furthermore, in the population of Kuira-gawa River, some small reddish orange dots on the cheek, the lower half of operculum, and gill membrane in males ( Fig. 6G), but many densely-arranged dots are present in those of the other populations; females lack orange spots on the lower half of body, whereas many spots are seen in those of the other populations ( Fig. 6H).

Distribution and habitat. Rhinogobius aonumai aonumai is known only from Iriomote-jima Island, the Yaeyama Group of the Ryukyu Islands, Japan. In this island, it is seen in the upper reaches of freshwater streams above waterfalls in montane areas of Geta-gawa, Hinai-gawa, Kura-gawa, Nakara-gawa, Nishida-gawa, Urauchi-gawa and Yuchin-gawa rivers, and the upper reaches of swift freshwater streams without waterfalls of Aira-gawa and Kuira-gawa rivers. In addition, we identified the gobies in the photographs taken from Arabara-gawa, Hora-gawa, and Nakama-gawa rivers registered in the Image Database of Fishes, as R. a. aonumai . The subspecies is usually found in small pools of streams, called “Fuchi” in Japanese.

Etymology. The specific/subspecific name, aonumai , refers to Dr. Yoshimasa Aonuma, who was the pioneer in the taxonomic study of the genus Rhinogobius in the Ryukyu Islands. In his master's thesis, he was the first to suggest that the number of vertebrae in Rhinogobius sp. YB from the Yaeyama Group of the Ryukyu Islands was higher than those from other islands of the Ryukyu Islands ( Aonuma, 1992).