Rhynchobatus immaculatus, Last, Peter R., Ho, Hsuan-Ching & Chen, Rou-Rong, 2013

Last, Peter R., Ho, Hsuan-Ching & Chen, Rou-Rong, 2013, A new species of wedgefish, Rhynchobatus immaculatus (Chondrichthyes, Rhynchobatidae), from Taiwan, Zootaxa 3752 (1), pp. 185-198 : 187-196

Rhynchobatus immaculatus sp. nov.

( Figures 2–8 , Table 1 )

Holotype. NMMB–P16274, immature male 730 mm TL, Keelung fish market, Taiwan, 16 Mar. 2012, purchased from market by P. Last, field no. HO–179.

Paratypes. 3 specimens: CSIRO H 7418–01, immature male 890 mm TL, Wu-chi fish market, Taichung County, Taiwan Strait, western Taiwan, ca. 24°18’N, 120°29’E, 21 May 2010, purchased from market by H. Ho; NMMB–P16135, female 780 mm TL, Keelung fish market, Taiwan, 9 Mar 2012, purchased from market by H. Ho; NMMB–P16275 [HO–180], female 740 mm TL, collected together with holotype.

Non-types. 6 specimens: ASIZP 63513, immature male 408 mm TL, Ao-di, Taipei county, northeastern Taiwan, ca. 25°03’N, 121°56’E, 17 Jul. 2001, coll. Z.-H. Wu; ASIZP 66972, female 835 mm TL, Da-xi, northeastern Taiwan, 5 Feb 2007; NMMB–P16225, immature male 744 mm TL, Da-xi, Yilan County, northeastern Taiwan, ca. 24°56’N, 121°54’E, 13 Mar 2012, purchased from market by P. Last; NMMB–P16224, immature female 915 mm TL, Wu-chi fish market, Taichung, Taiwan Strait, western Taiwan, ca. 24°18’N, 120°29’E, 10 Apr 2012, purchased from the market by H. Ho; NMMB–P15684, immature male 992 mm TL, collected together with CSIRO H 7418–01; NMMB–P15661, immature male 591 mm TL, Wu-chi fish market, Taichung, Taiwan Strait, western Taiwan, ca. 24°18’N, 120°29’E, 11 Sep 2011, purchased from the market by H. Ho.

Diagnosis. A medium-sized species of the genus Rhynchobatus with the following combination of characters: a broad, wedge-shaped snout; preoral snout 19–21% TL; eye small, length 4.1–4.5 in preorbital snout; interorbital space 2.6–2.9 in preorbital snout; tooth rows about 48; spines absent from snout; supraorbital spines small, well differentiated, extending from preorbit to beyond end of spiracle; predorsal spines relatively well developed; two disjunct rows of 6–9 small scapular spines on each side of disc; predorsal space 48–49% of total length; origin of first dorsal fin well behind origin of pelvic-fin bases; dark greenish brown dorsally with a few white spots scattered on pectoral disc; black pectoral marking absent; prominent row of white spots commencing just forward of a single white spot (above pelvic-fin origin) and coalescing posteriorly to form a white mid-lateral line on tail; orbital membrane white with dark bar over eye; no alternating light and dark markings on interorbital space; total pectoralfin radials 65–68; vertebrae with 28–30 monospondylous precaudal centra, 124–131 precaudal free centra, 38–42 diplospondylous caudal (free) centra, 165–170 total free centra, 179–184 total centra (including synarcual centra).

Description. Body relatively robust; snout in front of eyes bluntly angular to obtusely wedge-shaped, angle about 50° in holotype (52–53° in paratypes). Lateral margin of snout slightly convex beside orbit, otherwise almost straight. Preorbital length 3.3 in holotype (3.3–3.4 in paratypes) times interorbital width. Preoral length 3.4 (3.0– 3.3) times mouth width. Disc width across pectoral-fin apices 75% (75–77%) of disc length from snout tip to pectoral-fin free rear tips. Head strongly depressed, trowel-shaped, disc thickness 1.5 (1.6–1.7) times in interorbital space; ventral head length 3.2 (3.2–3.4) times in total length; surface between eyes and spiracles almost flat. Precloacal length 85% (86–88%) of length of tail from anterior vent to caudal-fin tip. Tail moderately depressed; in cross section, arched dorsally, almost flat ventrally, angular ventrolaterally at lateral keels, tapering evenly from pelvic-fin insertions. Width of tail at first dorsal-fin insertions of holotype 1.8 (1.6–1.9) times interspiracular distance. Lateral keels extended forward as a thickened angular edge along precaudal tail, reaching forward to below posterior half of first-dorsal fin; strongly differentiated on anterior part of caudal fin.

Horizontal eye (eyeball) diameter about 63% (64–67%) of interspiracular width, distance from anterior margin of orbit to posterior margin of spiracle slightly smaller than interspiracular width; greatest dimension of spiracles 58% (47–50%) of horizontal eye diameter; distance between spiracle and eye less than a fifth horizontal eye diameter, membrane of orbit almost continuous with spiracular opening. Spiracle dorsolateral, anterior margin with a partly concealed thickened valve, posterior margin with two short anteriorly directed spiracular folds; outer fold slightly taller and larger than inner fold.

Nostrils diagonal, forming about a 45° angle with body axis, incurrent aperture directed more laterally. Nasal cavity fully exposed, without dividing flaps; aperture straight anterolaterally, recurved posteromedially. Anterior nasal flap narrow, low, anteromedial on nasal aperture, inserted near midlength of nasal aperture; anterior process short, bilobed, its base length about twice as long as its width. Posterolateral nasal flap low, narrow and elongated, weakly lobate; originating just behind anterior lateral edge of incurrent aperture, extending posteriorly to about midlength of nasal aperture. Posterior nasal flap low, short based; joined to undersurface of posterolateral flap near anterior third of its length, junction concealed beneath posterolateral nasal flap; inserted near posterior quarter of nostril. Nostril width 1.3 (1.2) times in internarial width.

Mouth opening somewhat arcuate, weakly undulating to nearly straight laterally; strong medial depression on upper jaw corresponding to a very prominent anterior protrusion at symphysis of lower jaw; much weaker corresponding depressions and convexities laterally. Labial folds and furrows short, but well developed at corners of mouth; shallow pockets, circumoral grooves, and low folds and depressions, surround jaws laterally to labial folds; grooves most prominent on lower jaw. Teeth in quincunx, about 48 rows in both upper and lower jaws of paratype CSIRO H 7418–01. First four gill openings subequal in length, the fifth slightly shorter. Third gill opening 2.6 (2.3–2.6) in internarial width, 3.3 (2.8–3.1) times in nostril length, 1.2 (1.2–1.7) times length of fifth gill opening.

Dermal denticles minute, covering all of body surface, varying in shape and size over body ( Figure 7 ). Denticles with slender pedicels and elevated crowns; crowns rhomboidal, subcircular to broadly ovoid, margins irregularly rounded to crenulate anteriorly; crowns weakly unicuspidate, rounded or tricuspidate posteriorly, usually with prominent medial and lateral ridges. On snout, broadly ovoid, textured with 3–5 pronounced longitudinal ridges; median ridge best developed; posterior margin weakly tricuspidate; scales in two main sizes, weakly imbricated with some gaps ( Figure 7 a). On interorbit, somewhat similar to snout ( Figure 7 b); those on orbital membrane slightly smaller than those on interorbit; an indistinct patch of slightly enlarged (often more elongate) denticles present in front of eyes. On mid-dorsal surface, more regular in size, dense, often weakly imbricate; narrow patches of skin exposed where scales are missing; posterior margins irregular to rounded ( Figure 7 c). On outer pectoral fin, much smaller, similar to those of snout ( Figure 7 d). On flank below first dorsal fin, similar to outer pectoral fin but relatively much broader ( Figure 7 e). On ventral surface, subrhomboidal, usually acuspid, strongly imbricate; slightly larger than on dorsal flank but mostly smaller than on disc ( Figure 7 f).

Small, variable-sized spines present on dorsal surface of body and tail; present in series on orbital margin, along dorsal midline of disc and tail, and in scapular region; those of nuchal and mid-scapular regions largest; rostral spines absent. Spines along midline of disc and tail narrow and long based or globular and weakly oblique; distal surfaces of globular spines smooth, with corrugated bases; keel-like spines with corrugated bases and sometimes lateral edges. Orbit of paratype CSIRO H 7418–01 with a single, continuous series of ca. 20, small, variable-sized spines; series extending along inner margin of orbit from anterior mid-eye to beyond posterior margin of spiracle; similar in form to those along midline; row partly interrupted above mid spiracle in some types (partially subdivided into orbital and spiracular groups of spines). Predorsal series with ca. 27 spines of varying size in CSIRO H 7418–01, well developed, spines partly embedded in a low, cutaneous ridge; extending from anterior nuchal region to over pelvic-fin origin; spine bases often within a shallow groove; closely and more or less evenly spaced anteriorly, more widely spaced posteriorly. Interdorsal series barely emergent; absent and not forming a ridge behind second dorsal fin. Scapular spines of CSIRO H 7418–01in two short, disjunct, linear series of on each side of disc; commencing just behind origin of predorsal series, terminating at level of pectoral-fin apex; anterior series with ca 8–9 spines, its length subequal to eye diameter; posterior series with 6–9 spines, short, slightly longer than anterior series; no obvious lateral patches present.

A Dorsal fins similar in shape in young, raked, shark-like, with convex anterior margins (shallowly concave at base), bluntly pointed apices, deeply concave posterior margins, sharply acute free rear tips, and straight inner margins. Inner margin of first dorsal fin about twice (1.9–2.0 times) in its base length. First dorsal fin larger than second; origin just forward of mid-base of pelvic fins; free rear tip slightly behind free rear tips of pelvic fin.

Interdorsal space 2.8 (2.3–2.7) times length of first dorsal base, 3.5 (2.9–3.3) of length of second dorsal-fin base. Caudal fin rather short, strongly forked; dorsal caudal margin 6.5 (5.9–6.5) in total length, subequal to interdorsal space. Dorsal caudal margin strongly convex, weakly concave near its origin; tip bluntly pointed. Preventral caudal margin strongly convex; ventral lobe well developed, tip strongly angular. Lower postventral caudal margin short, weakly concave, 2.9 (2.2–3.2) in length of upper margin. Upper postventral margin weakly concave. Caudal axis elevated slightly, forming a narrow angle to main body axis. Pectoral fin originating at about level of spiracle, with initially concave then convex anterior margins; apices broadly pointed, posterior margins moderately convex; free rear tips narrowly rounded, extending 101% (85–89%) of distance between pectoral and pelvic-fin bases (pectoral– pelvic space); inner margins straight to weakly concave. Pelvic fins small, with weakly convex to straight anterior margins, broadly rounded apices, weakly concave posterior margins, elongate and very narrowly rounded free rear tips, and concave inner margins; inner margin very long, 1.5 (1.3–1.5) times length of pelvic base; fin base 1.0 (0.9) in pectoral–pelvic space; height of pelvic fin about 2.1 (2.0–2.3) in their length. Distance between pelvic-fin insertions much longer than pelvic-fin base length. Vent with well-developed folds laterally; well separated from pelvic-fin inner margins. No data on adult clasper.

Holotype Paratypes (n=3)

Min Max Mean Vertebral column with 184 (179–181) total centra (excluding segments); 14 (14–15) synarcual centra, 28 (29– 30) monospondylous centra, 131 (124–127) precaudal free centra, 39 (38–42) diplospondylous caudal (free) centra, 170 (165–166) total free centra. Total synarcual segments 7.6% (7.8–8.3)%, monospondylous 15.2% (16.1– 16.8)%, diplospondylous precaudal centra 56.0% (51.9–54.2)%, and precaudal free centra 71.2% (68.5–70.9)% of total centra count. Total pectoral radials 65 (66–68): 4 (5–7) free radials before propterygium, 22 (22) propterygials, 5 (5) mesopterygials, 5 (6) neopterygials, 29 (28) metapterygials, 61 (59–61) total basal radials (excluding free radials).

Colour (when fresh). Based on holotype NMMB–P16274 unless stated otherwise: Dorsal surface of body mostly medium to dark greenish brown (becoming greyish on preservation); paler, yellowish brown laterally beside rostral cartilage on snout and along hind margins of pectoral and pelvic fins; black pectoral marking absent, instead region plain or with 1 (1–3 in paratypes) small, diffuse-edged white spots; a few similar, isolated white spots near insertion of pectoral fins; single white spot above origin of pelvic fin; a few white spots at bases of dorsal fins (sometimes also beneath their inner margins); a well-developed, single row of small white spots on flank originating over origin of pelvic fin, then coalescing beneath first dorsal fin to form a narrow white stripe; stripe extending along dorsolateral surface of each side of tail to anterior part of caudal peduncle; dorsal and caudal fins yellowish brown, paler than body, tips dusky; orbit white with a broad black bar on its upper surface; suborbit pale; interorbit with a white spots on each side near obit and with or without a dark medium blotch. Ventral surface almost uniformly white, strongly contrasted with dorsal surface; anterior half of snout either side of rostral shaft with broad, irregular, semicircular, blackish patch (faint is some preserved material); dark patch also between nostrils in NMMB–P16275; pectoral-fin with narrow dusky tips. In preservative, pale areas on dorsal surface becoming more strongly demarcated from darker areas adjacent.

Size. Reaches at least 99 cm TL (non-type NMMB–P15684), but this specimen and all five other males examined (41–89 cm TL) were immature. The dorsal and caudal fins were well developed in NMMB–P15684 (see Figure 4 ), so it is likely to be a medium-size wedgefish with a maximum length less than 150 cm. An investigation of size structure in the Taiwanese population is needed.

Distribution. Known from seas adjacent Taiwan. Possibly more widespread locally in the western North Pacific, but positive confirmation is needed as these fishes are frequently mis-identified.

Etymology. The epithet, immaculate, is a combination of the Latin im (not) and macula (spot, mark), and is based on the lack of a dark pectoral marking (rather than any white spots) which is otherwise present in small individuals of other nominal species of Rhynchobatus . Vernacular: Taiwanese Wedgefish.

Remarks. The Taiwanese Wedgefish, Rhynchobatus immaculatus , undergoes ontogenetic changes in fin shape that typify development in many other chondrichthyan fishes. The dorsal fins change shape to become taller and more erect as they develop (see Figure 4 ). The first dorsal fin becomes more pointed apically ( Figures 4 a, d), and the caudal-fin lobes become relatively longer and narrower ( Figures 4 c, f). These changes, which take place within a relatively narrow size range (immature males NMMB–P16274 and NMMB–P15684 are 730 mm and 992 mm TL respectively) in R. immaculatus , are likely to be associated with onset of maturity.

Rhynchobatus immaculatus differs from other wedgefishes occurring in the western North Pacific, primarily in vertebral count and coloration. It has a very high vertebral count matched only by R. djiddensis from the Indian Ocean; total free centra of R. immaculatus 165–170 vs. typically more than 174 in R. djiddensis . Another high count species R. australiae , has been confirmed from Taiwan (HUMZ–109480, female 790 mm TL; total free centra 161) but, like R. djiddensis , has a more complex colour pattern and a black pectoral marking in small individuals. Rhynchobatus immaculatus also appears to be a smaller wedgefish than either R. australiae or R. djiddensis , which both attain about 300 mm TL (Compagno & Last, 1999) and 310 mm TL (Compagno et al., 1989) respectively. An undescribed species from the Indo –Malay Archipelago, Rhynchobatus sp. 1 (sensu Compagno & Last, 1999), which also has a dark, white-spotted body and lacks a dark pectoral marking, has a longer snout and much lower vertebral count (113–116) than R. immaculatus . All other species occurring in the region have a dark pectoral marking and lower vertebral counts: R. springeri has 113–126 free vertebral centra and R. palpebratus has 135–139 free vertebral centra (Compagno & Last, 2008). Also, the first dorsal fin is more posteriorly positioned in R. immaculatus (predorsal length 48–49% TL vs. 42–45% (mean 43%) TL and 43–48% (mean 46%) TL in R. springeri and R. palpebratus respectively.

Compagno & Last (1999) considered Rhynchobatus yentinensis Wang , described from a specimen taken at nearby Wenzhou, China, to be a possible synonym of R. springeri (their former R. sp. 2), but later considered it more likely to be synonymous with R. laevis (Bloch & Schneider, 1801) (Compagno & Last 2008; Eschmeyer, 2013). Wang’s (1933) account of the male holotype (1010 mm TL) gives an upper tooth row count of 27 (much lower the 52 rows in the smaller holotype of R. springeri and R. palpebratus , or the 48 rows in a smaller type of R. immaculatus ). The holotype of R. yentinensis once existed as a mounted skin but is now missing. According to Prof. Han-Lin Wu (Shanghai Ocean University, pers comm. to Xiaoyu Kong), most type specimens in Chinese collections from the early 1900s were lost during the Second World War. However, based on Wang’s description, R. yentinensis has a dark spot on the snout (vs. absent in R. immaculatus ), first dorsal-fin origin above or slightly behind the pelvic-fin origin (vs. first dorsal-fin origin well behind pelvic-fin origin), 2 spines in inner scapular rows on disc (vs. 6–9 spines), 2 series of white spots (vs. none) along the tail of males about 100 cm TL, and possibly a relatively shorter snout (preorbital length 2.4 times space vs. 2.6–2.9 times width of interorbital space). From the illustration and description of the holotype, R. yentinensis appears to be a broad-snouted species with a dark pectoral marking and low scapular spine count, suggesting that it is closer to either R. palpebratus or R. springeri , than to R. immaculatus . Its placement will have to be decided using molecular analysis, if the holotype is ever rediscovered and DNA can be extracted from the skin.

Figures

FIGURE 2. Rhynchobatus immaculatus sp. nov. immature male holotype (NMMB – P 16274, 730 mm TL, recently preserved). A. dorsal view; B. ventral view.

FIGURE 3. Rhynchobatus immaculatus sp. nov. View of central dorsal disc of immature male holotype (NMMB – P 16274, 730 mm TL, preserved) showing markings and the spine rows.

FIGURE 4. Rhynchobatus immaculatus sp. nov. fin shape and development. Immature male holotype (NMMB – P 16274, 730 mm TL, recently preserved): A. Lateral view of first dorsal fin, C. Lateral view of second dorsal fin, E. Lateral view of caudal fin. Immature male non-type (NMMB – P 15684, 992 mm TL, preserved): B. Lateral view of first dorsal fin, D. Lateral view of second dorsal fin, F. Lateral view of caudal fin.

FIGURE 5. Rhynchobatus immaculatus sp. nov. Snout and orbito-spiracular region of immature male non-type (NMMB – P 15684, 992 mm TL, preserved).

FIGURE 6. Rhynchobatus immaculatus sp. nov. View of oronasal region and snout immature male holotype (NMMB – P 16274, 730 mm TL, recently preserved).

FIGURE 7. Rhynchobatus immaculatus sp. nov. SEM images (x 100) showing squamation on the left side of a immature male nontype (NMMB – P 15684, 992 mm TL, preserved). A. Snout; B. Supraorbit; C. Mid-disc; D. Pectoral fin; E. Flank beneath first dorsal fin; F. Ventral anterior tail. Letters correspond to those in the Figure 1.

FIGURE 8. Distribution of Rhynchobatus immaculatus sp. nov. Yellow star—holotype; yellow dots—market sites for other material. Map extracted from Google Earth.

Tables

TABLE 1. Morphometric data for the immature male holotype (NMMB – P 16274) and paratypes (CSIRO H 7418 – 01, NMMB-P 16275 & P 16135) of Rhynchobatus immaculatus sp. nov. Measurements are expressed as percentages of total length. Data for paratypes are expressed as minima, maxima and means.

	Holotype	Paratypes (n=3)
		Min Max Mean
TOT—Total length	730	740 889
FOR—Fork length	92.7	91.5 92.8 92.2
PCL—Precaudal length	83.7	83.2 84.6 84.0
PD2—Pre-second dorsal length	70.7	69.2 70.4 69.8
PD1—Pre-first dorsal length	48.8	47.8 48.4 48.2
PP2—Prepelvic length	45.8	44.1 45.6 44.7
SVL—Snout–vent length	46.0	44.5 46.8 45.8
PSP—Prespiracular length	21.7	21.1 21.4 21.2
PG1—Prebranchial length	27.5	25.5 27.3 26.5
HDL—Head length	31.4	29.6 31.0 30.5
POB—Preorbital length (direct)	17.7	16.0 17.0 16.7
POR—Preoral length	21.1	19.3 20.5 20.0
PRN—Prenarial length	16.7	15.2 16.3 15.9
IDS—Interdorsal space	16.2	15.5 16.2 15.9
DCS—Dorsal–caudal space	9.2	8.8 9.6 9.2
PPS—Pectoral–pelvic space	4.8	5.2 5.3 5.2
PCS—Pelvic–caudal space	34.7	33.8 34.4 34.1
PDS—Pelvic–dorsal space	2.9	2.4 3.0 2.7
DW—Disc width	33.8	33.1 34.2 33.6
DL—Disc length	45.1	43.4 44.9 44.1
DT—Disc thickness	8.3	8.1 8.3 8.2
Snout—Greatest width	34.7	32.8 33.1 33.0
SWB—Snout width at base	16.3	15.3 16.6 16.0
COL—Corneal/eye length	2.4	1.7 2.5 2.2
COH—Corneal/eye height	1.2	0.9 1.4 1.2
EYL—Eye [eyeball] length	3.9	3.9 4.1 4.0
EYH—Eye (eyeball) height	2.6	2.4 2.6 2.5
INO—Interorbital space	5.4	4.9 5.1 5.0
SPL—Spiracle length	1.5	1.3 2.2 1.6
SPH—Spiracle height	2.2	1.9 2.0 2.0
ESL—Eye–spiracle space	5.6	5.3 5.6 5.4
INS—Interspiracular space	6.1	5.9 6.4 6.1
NOW—Nostril width	5.1	4.8 4.9 4.8
INW—Internarial space	4.0	3.9 4.2 4.0
ANF—Anterior nasal flap length	2.0	1.7 1.8 1.8
NSE—Nostril to snout edge	1.7	1.5 1.6 1.5
MOL—Mouth length	0.5	0.4 0.5 0.4
MOW—Mouth width	6.1	6.2 6.5 6.3
GS1—First gill slit height	1.7	1.4 1.8 1.6
GS2—Second gill slit height	1.7	1.6 1.8 1.7
GS3—Third gill slit height	1.5	1.5 1.7 1.6
GS4—Fourth gill slit height	1.5	1.4 1.7 1.5
GS5—Fifth gill slit height	1.2	1.0 1.3 1.2 ...... continued on the next page