Tomiyamichthys hyacinthinus, Sato & Motomura, 2025

Tomiyamichthys hyacinthinus sp. nov.

[New English name: Double-filamentous Shrimpgoby; new standard Japanese name: Hotarubi-Onihaze]

Figures 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ; Tables 1–2 View TABLE 1 View TABLE 2

Flabelligobius sp. 3 : Senou et al., 2004: 291, unnumbered figs. (Iriomote-jima island, Yaeyama Islands, Japan; Okinawa Prefecture, Japan).

Tomiyamichthys sp. 3 : Senou et al., 2021: 297, unnumbered figs. [same photos as in Senou et al. (2004)].

Tomiyamichthys sp. : Tashiro et al., 2022: 259, unnumbered figs. (west of Satsuma Peninsula, Minami-satsuma, Kagoshima Prefecture, Japan).

Holotype. KAUM –I. 188639, male, 35.5 mm SL, north side of Ohto Port , Kataura , Kasasa, Minami-satsuma, Kagoshima, Japan, 31°25′25′′N, 130°10′16′′E, 18 m depth, 24 Aug. 2023, M. C. Sato. GoogleMaps

Paratypes. 3 specimens (29.0– 38.8 mm SL), collected from same locality and depth as holotype: KAUM–I. 188409 , male, 33.9 mm SL, 15 Aug. 2023; KAUM–I. 189168 , female, 38.8 mm SL, 30 Aug. 2023; KAUM–I. 191994 , male, 29.0 mm SL, 17 Nov. 2023, M. C. Sato .

Diagnosis. A new species of Tomiyamichthys with the following combination of characters: dorsal-fin rays VI-I, 9; anal-fin rays I, 9; pectoral-fin rays 17; lateral-line scales 45–48 (modally 45); transverse scale rows 14 or 15 (15); gill rakers of first gill arch 4 + 8 or 9 (9); prepelvic region partially scaled; a pale blotch on membranes between fourth and fifth spines of first dorsal fin; second and third spines of first dorsal fin elongated, filamentous with orange bands in males; fourth spine of first dorsal fin longer than first spine in males; first dorsal fin trapezoid, without filamentous spines in females; 2 or 3 transverse rows of yellow blotches anteriorly and longitudinal yellow bands posteriorly on caudal-fin membrane.

Description. Counts and measurements given in Table 2 View TABLE 2 . Body compressed, elongated, deepest at pelvic-fin origin. Head compressed, broader than high. Snout short, its length less than pupil diameter. Eyes close together, slightly interrupting head contour. Deep trough distinct around eye, from interorbital to postorbital regions. Interorbital space extremely narrow, eyes nearly in contact with each other. Mouth terminal, oblique, forming angle of about 30° to horizonal axis of body; posterior margin of maxilla level with or slightly beyond posterior margin of pupil. Lower jaw extending posteriorly slightly beyond upper jaw. Cheek bulging. Occipital region slightly narrower than nape width, separated from upper margin of cheek by curved groove. Interorbital space narrower than pupil diameter. Anterior nasal with short tubular opening just behind anterior margin of upper jaw; no fleshy flap at tip of anterior naris. Posterior nasal with very short tube at ca. midpoint between anterior nasal opening and anterior margin of pupil.

Teeth in both jaws incurved, slender and pointed (not canine-like), large anteriorly, smaller posteriorly; anterior part of upper and lower jaws with three and four rows of teeth, respectively, narrowing to single row posteriorly.

Tip of tongue blunt, free from mouth floor. Gill opening wide, extending to about level of posterior edge of preopercle; ventral two-thirds of lower part of gill slit closed by membrane; gill membranes attached only anteriorly to isthmus; gill rakers poorly developed.

Cephalic pores and papillae rows ( Fig. 3 View FIGURE 3 ) well developed; large pore (B′) immediately adjacent to each posterior nostril; two single pores (C and D) anteriorly and posteriorly, respectively, on interorbital; pore (E) dorsoposteriorly behind orbit; two postocular pores (F and G); three preopercular-canal pores (M′, N and O′).

Longitudinal papillae rows ( Fig. 3 View FIGURE 3 ) on lateral surface to ventrum of head, as follows: a single row along posterior margin of orbit; three rows across cheek; two rows from preopercular-canal pore O′, along lower margin of preopercle to just behind lower lip.

Scales generally cycloid, weakly ctenoid on caudal peduncle and base of caudal fin, progressively larger posteriorly; scales absent on head and pectoral-fin base; prepelivic region partially scaled (under skin) ( Fig. 3C View FIGURE 3 ); fins without scales, except two or three rows on base of caudal fin.

Origin of first dorsal fin slightly behind posteriormost base of pelvic fins; second dorsal fin close to, but separated, from first; all dorsal-fin spines slender, flexible; first spine relatively short, slightly shorter than fourth spine; second and third spines longer, filamentous in males; first to fourth spines almost same length (not elongated) in females. All segmented rays of second dorsal fin branched; ninth ray extending to caudal fin when lowered. Origin of anal fin below base of first segmented ray of second dorsal fin; height of anal fin slightly less than second dorsal fin when spread; anal-fin spine slender, flexible; all segmented anal-fin rays branched. Caudal fin ovate. Pectoral fins rounded when spread, reaching posteriorly to below base of first or second dorsal segmented ray. Origin of pelvic fin slightly behind vertical through lowermost point of pectoral-fin base; posterior margin of pelvic fin reaching anus; pelvic fins fused medially by frenum (between spines) and interradial membrane (between innermost segmented rays); pelvic frenum moderately thin, with smooth posterior margin.

Live and fresh color ( Figs. 1A–C, E View FIGURE 1 , 2A View FIGURE 2 , 4 View FIGURE 4 ). Body generally grey, ventrally white, with numerous orange spots. Four large dark brownish saddle-shaped blotches on side; first below first dorsal-fin base; second below middle of second dorsal-fin base; third just behind and below second dorsal-fin base; fourth posteriorly on caudal punctual. Head generally brown, ventrally white, with numerous orange spots. Opercle dark brown with white margin.Anterior half and posterior end of jaw reddish-orange. Ground color of iris gold with narrow yellow ring around pupil. First dorsal fin translucent anterior to third spine, brown with white margin posteriorly; first spine white with 3 orange bands; filamentous part of second spine (males only) white with 3 (1–4) orange bands; filamentous part of third spine (males only) white with 2 (1 in KAUM–I. 191994) orange bands; pupil-sized black blotch on outer margin of membrane between third and fourth spines; pale blotch edged with black on outer margin of membrane between fourth and fifth spines (lost soon after anesthetization) ( Figs. 4B, D View FIGURE 4 ); orange spots interspersed on membrane posterior to fourth spine. Second dorsal fin with translucent yellow margin and 4–6 longitudinal rows of orange blotches. Caudal-fin membrane translucent, with 2 or 3 transverse rows of yellow blotches anteriorly and longitudinal yellow bands posteriorly. Anal fin white, with narrow longitudinal yellow and brownish semi-transparent bands. Pelvic fin white with orange spots. Pectoral fin translucent dorsally, white with orange spots ventrally.

Color in alcohol ( Figs. 1D View FIGURE 1 , 2C View FIGURE 2 ). Head brown dorsally, creamy-white ventrally. Ground color of body creamy-white; 4 large dark brownish saddle-shaped blotches laterally. First dorsal fin translucent anterior to third spine, brown with white margin posteriorly. Second dorsal, caudal, anal, pelvic, and pectoral fins uniformly translucent with dark brown pigment. All orange and yellow spots on head, body and fins (when fresh) faded.

Etymology. The specific name “ hyacinthinus ” is derived from Latin meaning “hyacinth”, in reference to the pale, black-edged blotch on the membrane margin between the fourth and fifth spines of first dorsal fin. “Double-filamentous Shrimpgoby” refers to the elongated second and third dorsal-fin spines of the species. “Hotarubi”, in the new standard Japanese name “Hotarubi-onihaze”, means the light emitted by fireflies, and refers to the faint glow-like (in life) blotch on the membrane margin between the fourth and fifth spines of first dorsal fin. “Onihaze” is the common Japanese name for Tomiyamichthys .

Distribution and habitat. Currently known only from southern Japan (Izu to Yaeyama islands). The specimens examined in this study were collected from Kasasa, southwest coast of Satsuma Peninsula, Kagoshima (southern Kyushu). In addition, the new species was identified on underwater photographs from Izu-oshima island (Izu Islands), Izu Peninsula (Shizuoka Prefecture), southern Shikoku (Koch Prefecture), southern Satsuma Peninsula (Kagoshima mainland), Amami-oshima island (Amami Islands), Okinawa-jima island (Okinawa Islands), and Iriomone-jima island (Yaeyama Islands) ( Senou et al., 2004, 2006, 2021; Tashiro et al., 2022; Honda et al., 2024; this study).

All specimens of T. hyacinthinus sp. nov. in this study were collected from a sandy bottom (18 m depth) off Satsuma Peninsula, Kyushu, Japan. Observations by MS confirmed a symbiotic association between solitarily or pairs and the snapping shrimp Alpheus randalli Banner & Banner, 1980 ( Alpheidae ).

Remarks. Although T. hyacinthinus sp. nov. possesses a greater number of total gill rakers than any other member of Tomiyamichthys [12 or 13 in T. hyacinthinus vs. 11 or fewer in other species ( Hoese et al., 2016)], its remaining morphological characteristics align closely with the diagnostic characters of the genus indicated by Hoese et al. (2016).

Although the new species is similar to T. latruncularius and T. eyreae in having filamentous dorsal-fin spines in males only, and nine rays in each of the second dorsal and anal fins ( Allen et al., 2019), it is clearly distinguishable by several key characters. In addition to possessing a greater number of gill rakers, the new species has the fourth spine of the first dorsal fin longer than the first spine [vs. the first spine being longer than the fourth spine in T. latruncularius and T. eyreae ; first and fourth spine lengths (% of SL) in T. latruncularius (SMF 12763) and T. eyreae (MZB 25112) measured as 22.0 and 16.0, and 25.5 and 24.9, respectively (this study)]. Additionally, the new species displays a distinctive pale blotch on the membrane (in life) between the fourth and fifth spines of the first dorsal fin in both sexes ( Fig. 4B, D View FIGURE 4 ), a color feature absent in T. latruncularius and T. eyreae ( Klausewitz, 1974; Allen et al., 2019). Furthermore T. latruncularius is easily distinguished from T. hyacinthinus by the greater number of transverse scales [18 in T. latruncularius (taken from Hose et al., 2016) vs. 14–15 in T. hyacinthinus ], and absence of prepelvic scales (see Hoese et al., 2016: table 3) (vs. partly scaled).

Tomiyamichthys eyreae is morphologically the most similar to T. hyacinthinus , with both species sharing prepelvic scales and a black blotch between the fourth and fifth spines of first dorsal fin. However, T. hyacinthinus can be distinguished from T. eyreae by the following combination of characters [ T. eyreae characters and counts from Allen et al. (2019)]: relatively fewer lateral scales [45–48 (vs. 53–55 for T. eyreae )]; second and third spines of first dorsal fin elongated, filamentous, fourth spine not elongated (vs. second to fourth spines elongated, filamentous); first to third dorsal-fin spines of males white with orange bands (vs. all filamentous dorsal-fin spines uniformly white); caudal fin with two or three transverse rows of yellow blotches anteriorly, longitudinal yellow blotches posteriorly (vs. posterior longitudinal blotches absent).

The genetic distances among the six species of Tomiyamichthys were estimated from partial sequences of the mtDNA COI gene, the molecular analysis showing p -distances between T. hyacinthinus and T. latruncularius , Tomiyamichthys elliotensis Allen, Erdmann & Dudgeon, 2023 , Tomiyamichthys lanceolatus ( Yanagisawa, 1978) , Tomiyamichthys oni ( Tomiyama, 1936) , Tomiyamichthys russus ( Cantor, 1849) , and Tomiyamichthys tanyspilus Randall & Chen, 2007 of 9.1–10.6%, 21.1–23.0%, 29.1–30.9%, 23.2–24.8%, 21.9–23.9%, and 27.3–29.1% respectively ( Fig. 5 View FIGURE 5 ).

Comparative material examined. MZB 25112 View Materials , holotype of Tomiyamichthys eyreae , male, 37.7 mm SL, Daram Island   GoogleMaps , southeast of Misool Island, Raja Ampat Islands, West Papua Province, Indonesia, 02°9′52′′S, 130°56′25′′E, 28 m depth, 16 Apr. 2019, M. V. Erdmann.