Chaunax obscurus, Ho & Ma, 2022

Ho, Hsuan-Ching & Ma, Wen-Chun, 2022, Four new species of the frogmouth genus Chaunax (Lophiiformes: Chaunacidae) from Taiwan and the Philippines, Zootaxa 5189 (1), pp. 146-179 : 163-168

Chaunax obscurus sp. nov.

Black-mouth frogmouth

Figs. 11 , 12A‒C , 13A‒E , 14A ; Tables 1‒3 , 5

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Holotype. NMMB-P34690 (254), ca. 24°30’N, 125°25.2’E, off Daxi , Yilan, northeastern Taiwan, northwestern Pacific Ocean, bottom trawl, ca. 200‒300 m, 25 Aug. 2020.

Paratypes. ASIZP 71252 (1, 175) , off Daxi , Yilan, 7 Jul. 2004 ; NMMB-P34691 (1, 187) , NMMB-P34692 (1, 180) , NMMB-P34693 (1, 170) , NMMB-P34694 (1, 164) , NMMB-P34695 (1, 141) , NMMB-P34696 (1, 133) , all collected together with holotype .

Etymology. The specific name, a Latin adjective meaning dark, refers to the black mouth cavity and gill chamber.

Diagnosis. Species of C. fimbriatus group distinguished from other members of that group by its black mouth cavity and gill chamber; skin covered with simple spinules; relatively short caudal peduncle (TL1=25.5% SL, TL2=17.9% SL, TL3=13.5% SL); 3‒5 spinules flanking neuromasts; fresh body coloration (orange-red with irregular small yellow patterns on dorsal surface, latter turning pale when preserved); yellowish green to brown esca; modal lateral-line neuromasts: BD 2, CD 6, DG 3 or 4, FG 3, GH 11 or 12; and P 13 or 14.

Description. Morphometric (expressed as % SL) and meristic data are provided in Tables 1‒3 , 5 . Following data provided first for holotype, followed in parentheses by range for paratypes, when different.

D III, 12; P 13; A 7; C 9. Lateral-line neuromasts: AB 11/12 (10‒12, mainly 11); AC 8/8 (7 or 8, mainly 8); BB 6; BB’ 6 (4‒6, mainly 6); BD 2/2 (2); CD 6/7 (6‒8, mainly 6); DG 4/4 (3‒5, mainly 4); EF 6/6 (5‒7, mainly 6); FG 3/3 (2 or 3, mainly 3); GH 10/11 (10‒12, mainly 11); BI 28/30 (28‒36), including 0/2 (0‒4) on caudal-fin base. Gill rakers: GRi 4+9=13 (3‒4+8‒10=12‒14); GRii 9 (8‒10); GRiii 1+10=11 (1+9‒10=10‒11), GRiv 8 (7 or 8).

Head length 2.3 (2.2‒2.4) in SL; head width 4.9 (4.5‒5.2) in SL, 2.1 (2.0‒2.2) in HL; pre-preopercular length 3.3 (3.1‒3.6) in SL, 1.4 (1.3‒1.5) in HL; predorsal length 2.1 (1.9‒2.1) in SL; pre-gill opening length 1.6 (1.5‒1.7) in SL; illicial length 11.5 (8.6‒11.5) in HL, illicial trough length 5.2 (5.3‒6.0) in HL; eye diameter 6.3 (4.7‒6.3) in HL; upper jaw 4.3 (4.2‒5.4) in SL, 1.9 (1.8‒2.3) in HL; post-dorsal fin length 6.3 (5.6‒8.1) in SL, 2.7 (2.4‒3.5) in HL; post-anus length 3.6 (3.2‒3.9) in SL, 1.6 (1.4‒1.7) in HL; post-anal fin length 9.4 (7.0‒9.4) in SL, 4.1 (3.0‒4.1) in HL; caudal peduncle depth 11.2 (10.2‒11.2) in SL, 4.9 (4.4‒4.9) in HL; caudal fin length 3.7 (3.2‒3.7) in SL, 1.6 (1.3‒1.6) in HL.

Body robust, relatively deep. Head globular with broad interorbital space, skull slightly elevated posteriorly. Trunk cylindrical. Skin thick, loose and flaccid; tips of pectoral- and pelvic-fin rays well connected by thick skin. Caudal peduncle relatively short and stout, somewhat cylindrical, tapering posteriorly.

Illicium short and stout; esca with thick central tongue bearing many yellowish-green to brown cirri. Illicial trough slightly concave, oval, about twice as long as wide, its length about equal to eye diameter.

Dermal spinules relatively short and stout; interspaces slightly greater than spinule length. Broad band of about 14 (10‒14) rows of dermal spinules in front of illicial trough; 3‒5 pairs of short spinules flanking neuromasts; interspaces of lateral-line neuromasts much longer than width of neuromast.

Teeth relatively slender and fang-like; band of about 8 (6‒8) irregular rows of teeth on upper jaw, those in middle portion slightly larger than rest, posterior one-third narrower than rest of band; band of 6 (5‒6) irregular rows of teeth on lower jaw, teeth slightly larger than those on upper jaw with those in innermost row slightly longer than others. Vomer with 2 bands of teeth separated by small gap, with about 4 (3 or 4) irregular rows in each band. Each palatine with single band of small teeth.

Cirri present on external surface of both jaws, interorbital space, membranes above eye, dorsal surfaces of head and body, lower part of premaxilla, lateral body and caudal peduncle; most cirri relatively strong and branched.

Coloration. When fresh ( Figs. 11A‒B , 13A‒E ), body covered with many irregular, 3‒8 mm wide yellow patches forming reticulate patterns on orange-red background, but ventral side paler. Cirri on esca yellowish-green to brown, those on body pale to orange red. In preserved state ( Figs. 13C , 14A ), markings faded to numerous irregular pale patches on light brown background and ventral side pale; cirri on esca deep brown, cirri on body pale; gill chamber black except for small pale region posteriorly, mouth cavity gray anteriorly but gradually becoming black posteriorly, gill arches gray, peritoneum black.

Distribution. Currently only known from type series collected off northeastern Taiwan at depths of around 300 m; likely an endemic species in this area.

Remarks. All of the present specimens of Chaunax obscurus sp. nov. were collected together with C. fimbriatus and C. viridiretis sp. nov. (described below) off northeastern Taiwan, but the first species was much less abundant than the other two. All three species are very similar to each other in coloration and morphology, but C. obscurus can be separated from C. fimbriatus by two distinct features, its lack of white patches dorsally ( Figs. 11 , vs. 15A) and its mainly black gill chamber ( Fig. 13E ; vs. pale, Fig. 13F , or sometimes with small irregular black patches). The dorsal white patches of C. fimbriatus are clear and distinct in both fresh and preserved condition and its color patches remain gray or brown in preserved specimens ( Fig. 14B ), whereas they fade in preserved specimens of C. obscurus ( Fig. 14A ).

Chaunax umbrinus Gilbert, 1905 , which inhabits the Hawaiian Islands and the Emperor Seamount chain (pers. data), is readily separable from C. obscurus by having very fine greenish-yellow patches on the dorsal surface ( Fig. 15B ), that turn brown when preserved to form a very fine pale reticulated pattern on a brownish background ( Figs. 14C ).

Figures

FIGURE 11. Chaunax obscurus sp. nov. A. Holotype, NMMB-P34690, 254 mm SL, fresh. B‒C. Paratype, ASIZP 71252, 175 mm SL, fresh (B) and preserved (C).

FIGURE 12. Dermal spinules of three other species in Chaunax fimbriatus species group, SEM. A‒C. C. obscurus sp. nov., NMMB-P34693, 170 mm SL: A, spinules beside neuromast; B‒C, skin above eye. D‒E. C. umbrinus, ASIZP 70334, 248 mm SL, skin above eye. F‒G. C. viridiretis sp. nov., ASIZP 64499, paratype, 165 mm SL, skin above eye.

FIGURE 13. Details of two species in Chaunax fimbriatus species group. A‒E. C. obscurus sp. nov. (A‒C, E, holotype; D, paratype, ASIZP 71252):A, dorsal view of head; B, dorsal view of dorsum; C, ventral view of left side of head; D, mouth cavity; E, dark coloration within right gill chamber. F. C. fimbriatus, NMMB-P34718, 211 mm SL, pale coloration within right gill chamber.

FIGRUE 14. Preserved coloration on dorsal surface of four species in Chaunax fimbriatus species group. A. C. fimbriatus, NMMB-P13862, 115.7 mm SL. B. C. obscurus sp. nov., ASIZP 71252, 175 mm SL. C. C. umbrinus, NMMB-P23460, 216 mm SL. D. C. viridiretis sp. nov., ASIZP 64503, 196 mm SL. Not to scale.

FIGURE 15. Fresh coloration of two species in Chaunax fimbriatus species group.A. C. fimbriatus, ASIZP 63257, 274 mm SL. B. C. umbrinus, ASIZP 70334, 248 mm SL, photo by J. E. Randall.