Okamejei picta, Ng & Ho & Joung & Liu, 2023

Ng, Shing-Lai, Ho, Hsuan-Ching, Joung, Shoou-Jeng & Liu, Kwang-Ming, 2023, Okamejei picta sp. nov., a new rajid skate from the South China Sea (Rajiformes Rajidae), Zootaxa 5278 (1), pp. 103-118 : 104-117

Okamejei picta sp. nov.

Figs. 1–9 , Tables 1–2

urn:lsid:zoobank.org:act:5CD9D2D9-582C-4A97-9BA3-E5AEE6AE2297

Holotype. NMMB-P 36013, 429 mm TL, adult male, ca. 19°N, 114°E, off western Dong-sha Atoll , South China Sea, depth ca. 300 m, bottom trawl, 19 February 2021, coll. C.-H. Lin.

Paratype. ASIZP0081116, adult male, 405 mm TL (snout slightly damaged), collected together with the holotype.

Diagnosis. A medium-sized species of Okamejei (~ 429 mm TL) with yellowish brown dorsal surface, densely mottled with small black circular to irregular spots; pale blotches present but indistinct; absence of prominent pair of pectoral markings and posterior ocellus; ventral surface entirely whitish; ventral sensory pores dark edged; and the following combination of characters: disc width 57.6–63.2% TL, disc length 75.4–78.1% disc width; tail long, length 116–118% distance from snout tip to rear of cloaca; tail very slender, height 80.0–84.4% width at its midlength; snout narrow and pointed, preorbital snout length 22.8–32.1% disc length; first dorsal-fin base length 20.9–25.0% distance from first dorsal-fin origin to tail tip; tip of clasper without component funnel; nuchal thorn small; total pectoral radials 73–76; trunk centra 27–31; total centra 123–126.

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Description. The following data are provided for holotype, followed by the value of paratype in parentheses. Disc quadrangular, length 78.1% (75.4%) width; angle in front of spiracles 70° (64°); axis of greatest width 60.4% (48.4%) of disc length; anterior margin double concave, moderately concave anteriorly to the snout tip, convex besides eyes, considerably concave besides and posterior to spiracles; apex very narrowly rounded; posterior margin slightly convex; free rear tip rounded.

Details of dorsal and ventral view of head are shown in Fig. 3 . Head rather short, preorbital snout length 59.0% (43.9%) head length, distance between orbits 13.4% (13.9%) head length; pre-upper jaw length 52.2% (42.1%) ventral head length. Snout tip produced and very narrowly pointed; fleshy process absent at tip. Distance between orbits 81.2% (76.9%) orbit diameter. Spiracle medium-sized, length 58.9% (60.0%) orbit diameter; its opening in distorted teardrop-shape. Nostril suboval; anterior nasal flap somewhat expanded, lobelike, partly covered beneath nasal curtain; posterior inner margin fully covered by nasal curtain; posterior lobes forming nasal curtain, produced posterolaterally, posterior margin with prominent fringes; distance between nostrils 54.5% (48.5%) distance between first gill slits, 101% (93.0%) distance between fifth gill slits.

Upper jaw prominently arched, continuous at symphysis; lower jaw in wide inverted V-shape; part of lateral teeth covered by lobe of nasal curtain. Teeth unicuspid, with subcircular bases near symphysis; arranged in longitudinal rows; main cusps slender, long, sharp, directed posteriorly in upper jaw, directed anteriorly in lower jaw, becoming shorter and oblique laterally.

Pelvic fins bilobed; anterior lobe short and slender, narrowly rounded distally, lateral margin entire, inner margin considerably incised; posterior lobe greatly elongate, length 17.6% (18.5%) TL, lateral margins straight, free rear tip rounded; inner margin rather shallow, connected to anterolateral margin of clasper; anterior lobe 73.9% (69.0%) posterior lobe.

Tail long and thin, moderately depressed; relatively narrow at base, slightly tapering gradually to tail tip, not expanded at midlength; width at first dorsal-fin 65.7% (54.7%) width at midlength of tail, 47.6% (32.6%) width at axil of pelvic fin; length from postcloaca 116–118% distance from snout tip to precloaca; anterior cross-section suboval, flat on dorsal and ventral surface of the whole tail; height 81.3% (58.7%) width at axil of pelvic fin, 79.8% (84.4%) width at midlength, 98.0% (93.3%) width at first dorsal-fin origin; lateral tail fold poorly developed, its origin slightly anterior to first dorsal-fin origin, extending to tail tip.

Dorsal fins small, subequal in size and shape ( Fig. 4C, D ); first dorsal-fin height 51.6% (52.7%) in base length; second dorsal-fin height 64.9% (67.2%) in base length; fins subtriangular, anterior margins oblique, posterior margins rounded and slightly convex; interdorsal space moderately wide, 97.9% (83.5%) in first dorsal-fin base length; distance from first dorsal-fin origin to tail tip 38.9% (38.0%) tail length; caudal-fin length 27.4% (25.4%) distance from first dorsal-fin origin to tail tip; first dorsal-fin base length 76.3% (98.1%) caudal-fin length. Caudal-fin epichordal lobe well developed, base long and low; its height greater posteriorly; tip pointed, its posterodorsal margin somewhat convex; well separated from second dorsal fin; hypochordal lobe poorly developed.

Orbital thorns small, smaller than alar and malar thorns, 2 (4) on preorbit, 5 (5) on orbit, directed posteriorly; one rudimentary nuchal thorn present; no thorns on scapular regions. Malar thorn patch with 20 (20) enlarged, strongly curved thorns in ca. 3 rows; main patch small, curved slightly, located at disc margin near eye and spiracle; thorns merging with bunches of smaller thornlets laterally, thorns near disc edge smaller; thornlets at anterior disc larger, decreasing in size posteriorly. Alar thorn patch with 34 (33) thorns, size subequal to tail thorns; embedded and directed posteromedially, in about 2–3 rows; patch narrow, length slightly longer than malar patch. Tail thorns variously developed, in three rows ( Fig. 4A, B ); row not staggered; 26 (21) predorsal thorns, weakly curved, with very small bases, size subequal to orbital thorns; interdorsal thorns small, 3 (1); median row poorly developed; thorns in median row weak, 11 (5) thorns, emerging near pelvic-fin rear tip, extending along length of predorsal tail in a single row; dorsolateral rows of similar size; with 15 (16) similar thorns on each side, almost continuous, extending from near pelvic-fin rear tip to first dorsal-fin origin (to first dorsal-fin base end in the paratype), located above mid-lateral tail, closer to thorns of median row. Denticles poorly developed, disc and tail mostly naked; confined to a moderately developed patch on snout tip dorsally; long, widely spaced, thorn-like denticles along anterior margin of disc from snout tip to an area anterior to alar thorn patch; confined to a small patch at snout tip ventrally; tail and posterior disc entirely naked; denticles short, prickle-like, sparsely distributed in patches.

Clasper well developed, stout, depressed, length 23.5% (26.3%) TL; tip pointed. Clasper external features included boss (bs), cleft (cf), spike (sk), terminal bridge (tb), pseudorhipidion (ps), rhipidion (rh), shield (sh) and sentinel (st) ( Fig. 5 ); bs rather expanded, situated between lower part of cf and sk; cf narrow, partitioned by tb; ps rod-like, situated between upper cleft and rh; rh bilobed, its distal tip barely extend to proximal end of cf; st moderately developed, positioned among rh, tb, bs and sk; sk sharp, rather straight, not hook-like; sh long, with sharp outer edge; component funnel not evident.

Clasper skeleton highly calcified, consists of basal, axial and terminal cartilages. Basal cartilages contain beta cartilage (β), basipterygium (bpv), and intermediate segments 1 (b1) and 2 (b2) ( Fig. 6 ); β cartilage long, situated dorsally of posterior half of b1 and the whole b2 cartilages; bpv slightly arched outwards, linked with pelvic girdle anteriorly and with b1 posteriorly; b1 and b2 short, length about half of bpv, both rod-like. Pelvic girdle with large, slightly arched puboischiadic bar; iliac region enlarged, with two obturator foramina (of) on each side; iliac process (ip) slightly curved inwards; lateral prepelvic process (lpp) long and narrow; lateral process (lp) very short, with rounded tips. Terminal cartilages comprise nine components: axial cartilage (ax), three dorsal terminal cartilages (dt1–3), two accessory terminal cartilages (at1, at2), ventral marginal cartilage (vm), dorsal marginal cartilage (dm), and ventral terminal cartilage (vt) ( Fig. 7A ); ax longest, slender, with a rounded tip; at1 Y-shaped, deeply forked, distal tip paddle-shaped, attaching proximally to vm and forming st externally; at2 slender, hook-like, with a flattened tip, alongside at1, joining the tip of at1 distally, and forming sk externally; dm long, slightly concave, with distal end very weakly bifurcated, both lateral and medial tips broadly rounded; dt1 moderate, shield-like, slightly concave proximally, covering ax, with a blunt tip; dt2 moderately short, attached to dm proximally, and dt3 distally; dt3 very slender, with pointed tips, proximally attaching dt2, distally attaching vt; vm long and forked, wide posteriorly, attached to ax and dm, distal tip forming ps externally; vt positioned at outer aspect of clasper glans, J-shaped, bifurcated proximally, broadly widened distally, tip spoon-shaped, forming sh and dk externally ( Fig. 8 ); not showing externally as component funnel.

Neurocranium ( Fig. 9 ) with a bullet-shaped anterior fontanelle (af); posterior fontanelle (pf) bottle-shaped, shorter than af; rostral cartilage (rc) long, length 59.0% (43.9%, note that the rostral cartilage is slightly broken in the paratype) of dorsal head length; rostral base (rb) moderately narrow, its width about one quarter of rc; antorbital cartilages (ac) thin, arched, attaching nasal capsule (nc) and the second segments of propterygium (pr); nc ovalshaped, preorbital canal foramen (poc) situated proximally to the leading edge of nc; preorbital process (prep) and postorbital process (postp) scarcely developed.

Distribution of ventral sensory pores overall W-shaped, denser on head, but sparsely distributed on other parts; pores in 1–2 rows at rostral cartilage, nasal curtain, area between gill silts, and pectoral fins before their maximum width; sensory pores present on anterior to middle edge of abdomen, absent from pelvic fins; pores generally small (slightly larger in paratype than holotype), those on area between gill gilts and on abdomen edge slightly larger, others rather small.

Meristics:Also provided in Table 2 . Tooth rows in upper jaw 40 (41); lower jaw 40 (40). Pectoral-fin propterygial radials 29 (28); mesopterygial radials 10 (8); metapterygial radials 37 (37); total basal radials 76 (73). Pelvic-fin radials 1 (1) + 19 (20). Trunk centra 31 (27); predorsal caudal centra 44 (43); predorsal centra 75 (70); centra between origins of dorsal fins 16 (16); diplospondylous centra 95 (96); total centra ca. 126 (123).

Coloration. When fresh ( Figs. 1–2 ), dorsal surface of disc, posterior pelvic-fin lobes, claspers and tail yellowish brown, densely covered by small black irregular spots; scattered larger blotches but indistinct; no prominent pair of pectoral markings and posterior ocellus; pectoral-fin margins translucent without spots or blotches; rostral cartilage uniformly pale brown, except for the posterior part with a few black speckles; dorsal fins and caudal fin translucent; eyelid brownish to translucent, eye dark; thorns pale, contrasted against darker dorsal surface of tail; tail strongly bicolored laterally, yellow dorsolaterally, pale ventralaterally; ventral surface of disc and tail uniformly whitish, pectoral fins slightly translucent; sensory pores dark edged, some surrounded by blotches. Coloration of female and juvenile unknown. In preservative, dorsal surface and sensory pores darker in general, others similar to fresh coloration.

Distribution. Known only from deep waters off western Dong-sha Atoll, South China Sea, at depth ca. 300 m.

Size. The types are both mature males (to 429 mm TL) and no information on females, juveniles and egg cases. Females presumably attain larger sizes.

Etymology. Derived from the Latin pictus, which means painted or colored, referring to the densely distributed black spots on the contrasting yellowish brown dorsal disc. Vernacular: Fine-spotted Skate.

Remarks. Among the genus Okamejei , O. picta sp. nov. resembles two other western Pacific species, viz., O. hollandi , and O. mengae . Both species share the characters of densely distributed black spots on the dorsal disc, and a ‘W-shaped’ distribution of ventral sensory pores ( Jeong et al. 2007; Misawa et al. 2022). However, the new species is readily distinguished from the two species by coloration patterns, morphometrics and vertebral counts ( Table 2 ).

The coloration and patterns of skates are sensitive to environmental influences, that the same species may have different colorations, and sympatric species may exhibit overlapping coloration patterns ( Weigmann 2017; Misawa et al. 2019; Gabbanelli et al. 2022). Thus, cautions should be taken when using coloration as diagnostic character in description of new species. Nevertheless, O. picta shows notable difference in several coloration patterns from O. hollandi ( Fig. 10 ): a yellowish brown dorsal disc (vs. grayish to dark brown in O. hollandi ); shape of the black spots on the dorsal disc circular to irregular (vs. uniformly circular); blotches indistinct (vs. distinct); posterior ocellus absent (vs. sometimes present); ventral disc mostly white (vs. pale to dark brown). By comparing the morphometrics, O. picta sp. nov. differs from O. hollandi in having shorter disc (45.0–47.7, vs. 51.6–55.8% TL); a larger head (dorsal-head length 24.5–24.8, vs. 19.3–21.5% TL); a longer distance between cloaca to first dorsal-fin origin (32.1–32.3, vs. 25.1–29.2% TL); a longer distance between cloaca to second dorsal-fin origin (41.1–41.9, vs. 34.1–39.6% TL); a longer tail (distance between cloaca to caudal-fin tip 53.6–55.1, vs 47.8–53.4% TL); space between nostrils relatively narrow, its length 23.5–23.6% (vs. 24.1–25.7% ventral-head length); a longer anterior pelvic lobe (12.8–13.0, vs. 10.3–12.1% TL); a longer posterior pelvic lobe (17.6–18.5, vs. 14.5–17.4% TL); distance between first dorsal-fin origin and caudal-fin tip small (20.9, vs. 22.2–25.7% TL); distance between second dorsal-fin origin and caudal-fin tip small (11.4–12.2, vs. 13.2–14.5% TL); and a shorter caudal fin (5.3–5.7, vs. 5.8–8.0% TL). In meristics, O. picta differs from O. hollandi in having more diplospondylous centra (95–96, vs. 66–83); more total centra (123–126, vs. 95–112); relatively few propterygials (28–29, vs. 29–32) and fewer total basal radials (73–76, vs. 82–86). When comparing clasper skeleton, the vt of O. picta is J-shaped, with a bifurcate proximal tip, while the vt of O. hollandi is weakly-curved in shape, with a blunt proximal tip ( Fig. 11 ). In O. picta , the component funnel at the tip of clasper is not evident, but it is prominent in O. hollandi . Furthermore, O. hollandi is a shallow water species, typically found in coastal waters not deeper than 100 m, while the two specimens of O. picta were captured in deepwaters (ca. 300 m).

Okamejei picta sp. nov. is also similar to O. mengae known only from the holotype, for which the validity is often questioned (e.g. Last et al. 2016; Misawa et al. 2022). Nevertheless, the new species is readily separated from O. mengae by having a combination of characters (data obtained from Jeong et al. 2007): blotches on the dorsal disc indistinct but present (vs. absent); a shorter disc (45.0–47.7, vs. 55.7% TL); a shorter snout (10.9–14.5, vs. 17.6% TL); a longer tail, distance between cloaca to caudal-fin tip 53.6–55.1 (vs. 48.5% TL); a much longer distance from second dorsal-fin origin to caudal-fin tip (11.4–12.2, vs. 5.8% TL); more trunk centra (31 vs. 23); and fewer total basal radials (73–76, vs. 96). Further comparisons on clasper morphology and skeleton are needed when adult males of O. mengae are available.

The presence of a component funnel at the tip of clasper was generally considered a diagnostic character of the genus (e.g. Last & Yearsley 2002; Last & Gledhill 2008; Last et al. 2010; Misawa et al. 2022), but Weigmann et al. (2015) excluded it from the diagnosis. In the description of O. ornata, Weigmann et al. (2015) found out that the component funnel was not evident, but the species share typical characters of genus Okamejei . Our results support Weigmann et al. (2015) that the presence of the component funnel may not be a diagnostic character of the genus. Okamejei picta sp. nov., shares all the diagnostic characters of Okamejei (defined in introduction) except for the absence of a component funnel, so the assignment of the new species to genus Okamejei is undoubted. Okamejei picta and O. ornata are the only two species without the component funnel in the claspers, but O. picta can be readily distinguished from O. ornata by having densely distributed black spots on the dorsal disc (vs. only patchy distributed blotches present) and a bifurcated proximal tip of vt (vs. tip not bifurcated).

Comparative materials. Okamejei hollandi : NMMB-P15670 (1, 476), Donggang fishing port, Pingtung , southwestern Taiwan, 31 Dec. 2010 . NMMB-P15678 (1, 415), Donggang fishing port, Pingtung, southwestern Taiwan, 18 Aug. 2010 . NMMB-P15680 (1, 460), Donggang fishing port, Pingtung, southwestern Taiwan, 3 Mar. 2010 . NMMB-P15682 (1, 460), Donggang fishing port, Pingtung, southwestern Taiwan, 3 Mar. 2010 . NMMBP16393 (1, 350), Ke-tzu-liao fishing port, Kaohsiung, southwestern Taiwan, 9 May 2010 . NMMB-P16757 (1, 426), Donggang fishing port, Pingtung, southwestern Taiwan, 10 Jul. 2010 . NMMB-P17093 (1, 462.5), Donggang fishing port, Pingtung, southwestern Taiwan, 9 Aug. 2012 . NMMB-P17262 (1, 480), Donggang fishing port, Pingtung, southwestern Taiwan, 6 Aug. 2012 . EBFS uncatalogued specimen (1, 432), Donggang fishing port, Pingtung, southwestern Taiwan, 10 Jan. 2022.

Figures

FIGURE 1. Fresh coloration of Okamejei picta sp. nov., NMMB-P36013, 429 mm TL, adult male holotype: top, dorsal surface; bottom, ventral surface.

FIGURE 2. Fresh coloration of Okamejei picta sp. nov., ASIZP0081116, 405 mm TL, adult male paratype: top, dorsal surface; bottom, ventral surface.

FIGURE 3. Details of dorsal (A, B) and ventral (C, D) views of snout area of Okamejei picta sp. nov.: A, dorsal view of adult male holotype (NMMB-P36013, 429 mm TL); B, dorsal view of adult male paratype (ASIZP0081116, 405 mm TL); C, ventral view of adult male holotype (NMMB-P36013, 429 mm TL); D, ventral view of adult male paratype (ASIZP0081116, 405 mm TL).

FIGURE 4. Details of thorns on midtail (A, B) and the dorsal-caudal area (C, D) of Okamejei picta sp. nov.: A, adult male holotype (NMMB-P36013, 429 mm TL); B, adult male paratype (ASIZP0081116, 405 mm TL); C, adult male holotype (NMMB- P36013, 429 mm TL); D, adult male paratype (ASIZP0081116, 405 mm TL).

FIGURE 5. Okamejei picta sp. nov., adult male holotype, NMMB-P36013, 429 mm TL, left clasper spread opened. bs, boss; cf, cleft; sk, spike; tb, terminal bridge; ps, pseudorhipidion; rh, rhipidion; sh, shield; st, sentinel.

FIGURE 6. Okamejei pictasp.nov., adult male holotype,NMMB-P36013,429 mmTL,X-radiograph of pelvic girdleandclasper basal cartilages (ventral view). ax, axial cartilage; β, beta cartilage; b1–2, intermediate segments 1 and 2; bpv, basipterygium; ip, iliac process; lp, lateral process; lpp, lateral prepelvic process of obturator foramina; pvp, pelvic propterygium.

FIGURE 7. Terminal skeleton of left clasper of (A) Okamejei picta sp. nov., adult male holotype, NMMB-P36013, 429 mm TL; and (B) Okamejei hollandi, EBFS adult male, uncatalogued specimen, 432 mm TL. ax, axial cartilage; at1–2, accessory terminal cartilage 1 and 2; dm, dorsal marginal cartilage; dt1–3, dorsal terminal cartilage 1–3; vm, ventral marginal cartilage; vt, ventral terminal cartilage.

FIGURE 8. Ventral terminal cartilage from left clasper of Okamejei picta sp. nov., adult male paratype, ASIZP0081116, 405 mm TL. (A) Dorsal view; (B) ventral view; (C) proximal tip viewed from left side.

FIGURE 9. Okamejei picta sp. nov., adult male holotype, NMMB-P36013, 429 mm TL, X-radiograph of neurocranium, snout and pectoral area. ac, antorbital cartilage; af, anterior fontanelle; cr, neurocranium; ms, mesopterygium; mt, metapterygium; nc, nasal capsule; pf, posterior fontanelle; poc, preorbital canal foramen, postp, postorbital process; pr, propterygium; prep, preorbital process; rb, rostral base; rc, rostral cartilage.

FIGURE 10. Fresh coloration of Okamejei hollandi, EBFS adult male, uncatalogued specimen, 432 mm TL: top, dorsal surface; bottom, ventral surface.

FIGURE 11. Ventral terminal cartilage from left clasper of Okamejei hollandi, EBFS adult male, uncatalogued specimen, 432 mm TL. (A) Dorsal view; (B) ventral view; (C) proximal tip viewed from left side.