Chelidoperca myathantuni, Psomadakis & Gon & Htut, 2021

Psomadakis, Peter N., Gon, Ofer & Htut, Thaung, 2021, Two new species of the genus Chelidoperca (Perciformes: Serranidae) from the Andaman Sea, eastern Indian Ocean, Zootaxa 4927 (1), pp. 87-103 : 88-93

Chelidoperca myathantuni sp. nov.

(New English name: Mya Than Tun’s perchlet)

Figures 1–3 , 5–8 , Table 1

Chelidoperca sp. A: Psomadakis et al. 2019: 385, Pl. XXVI, fig. 199 ( Myanmar coast).

Holotype. SAIAB 203716, 114.2 mm SL ( Fig.1A ), off Tanintharyi Coast , Myanmar, Andaman Sea, Indian Ocean, 13°3.21’N; 96°41.62’E, R / V Dr. Fridtjof Nansen, station 123, bottom trawl, 121–129 m depth, P.N. Psomadakis, 21 May 2015.

Paratypes. 14 specimens, 74.3–129.5 mm SL, all collected with bottom trawl in the Andaman Sea, off Myanmar’s Tanintharyi Coast by the R / V Dr. Fridtjof Nansen: SAIAB 203721 , 2 : 84.3–91.8 mm SL, same collection data as holotype. SAIAB 203723, 110.9 mm SL ( Fig. 1B ), same collection data as holotype. SAIAB 209600 , 4 : 91.6–129.5 mm SL, 10°2.70’N, 97°22.75’E, 125 m, station 154, 184 m depth, P.N. Psomadakis , 27 September 2018. SAIAB 209599 , 5 : 74.3–115.1 mm SL, 10°21.44’N; 97°25.10’E, station 149, 181– 183 m depth, P.N. Psomadakis , 26 September 2018. USNM 451517 , 99.5 mm SL and KAUM-I. 149193, 88.5 mm SL, both collected with SAIAB 209599 .

Diagnosis. A species of Chelidoperca distinguished from congeners by the following combination of characters: scale rows between lateral line and middle of spinous dorsal-fin base 3 (2 full-sized plus 1 half-sized); pored lateral-line scales 42–44 (modally 44); pectoral-fin rays 16; predorsal scales 7–8 (modally 7); scale rows absent from ventral side of dentary; scale rows on interorbital area extending to mid-orbit level; maxilla expanded posteriorly, covered ventrally by high skin fold; outermost row teeth of upper jaw distinctly enlarged; side of body with longitudinal dashed black stripe; 8–9 short white sub-triangular bars ventrally; dorsal-fin pale yellow with reddish pigment mostly restricted at base of spines and rays.

Description. Proportional measurements are given in Table 1 . Data for the holotype presented first, followed by paratype data in parentheses, if different. Dorsal-fin rays X, 10; anal-fin rays III, 6; pectoral-fin rays 16; pelvic-fin rays I, 5. Pored lateral-line scales 43 (42–44); cheek scale rows 6 (5–6), scale rows above lateral line 3 (2 full-sized plus 1 half-sized) ( Fig. 5A ); scale rows below lateral line 11 (10–11); predorsal scale rows 7 (7–8), circumpeduncular scales 20 (16–20). Gill rakers on upper limb 7 (5–7), gill rakers on lower limb 13 (12–14); developed gill rakers on upper limb 2 (2–3), developed gill rakers on lower limb 9 (9–10); total gill rakers 20 (17–20).

Body fusiform, slightly elongated, its depth less than head length, contained 4.1 (4.0–4.9) in SL; head length 2.5 (2.4–2.7) in SL; snout rounded, its length 10.6 (10.0–12.5) in SL; dorsal profile of snout forming an angle of ca. 30° with horizontal axis of head and body. Orbit large, its diameter 9.8 (8.6–10.1); interorbital width 31.7 (30.8–42.6) in SL. Mouth large, angled diagonally upwards; posterior margin of maxilla extending beyond vertical through midorbit, but not reaching vertical through posterior margin of orbit; upper jaw length 5.7 (5.3–5.8) in SL; lower jaw protruding well beyond upper jaw when mouth closed, its length 4.2 (4.1–4.5) in SL; maxilla expanded posteriorly and covered ventrally by high skin fold ( Fig. 6A ).

Upper jaw with a multi-serial band of mostly small, conical teeth, slightly tapering posteriorly; teeth of innermost rows near symphysis become gradually enlarged posteriorly; teeth of outermost row distinctly enlarged, those near symphysis largest, antrorse, caniniform, and gradually decreasing in size posteriorly. Lower jaw with narrower band of similar teeth, tapering posteriorly; outermost teeth enlarged on anterior part of jaw whereas innermost ones enlarged on posterior part of jaw. Vomer with V-shaped band of 3–5 rows of small conical teeth, with several enlarged and directed posteriorly on posterior portion. Palatine with 3–4 rows of small, conical teeth. Anterior nostril with raised rim anteriorly expanding to become fairly large skin flap posteriorly; posterior nostril oval.

Posterior margins of preopercle, interopercle and subopercle serrated, serrae on preopercle 35 (36 on right side) (17–36), interopercle 10 (8 on right side) (3–17) and subopercle 7 (8 on right side) (3–15). Opercle with 2 flat, prominent spines, upper spine longer than lower. Posttemporal with 2 (4 on right side) (1–4) serrae.

First supraorbital sensory canal pore at anterior edge of snout about the size of front row tooth of upper jaw; remaining pores tiny, in a series up to posterior nostril where they form two rows continuing into interorbital space. First infraorbital pore below posterior nostril, more or less at level of lower edge of pupil and similar in size to first supraorbital pore; at least 5 ventrally directed, similar size pores along ventral edge of lachrymal; remaining pores tiny, along edge of orbit. First mandibular-preopercular canal pore on chin anteriorly directed and followed by 4 round to slightly oval ventral pores, the posterior 3 usually accompanied by a smaller pore nearby. First (anterior) preopercular pore similar in size to ventral lachrymal pores, followed by many pairs of tiny pores dorsally.

Body and head covered with ctenoid scales, but snout and maxilla naked; lateral line slightly curved, terminating at caudal-fin base. Caudal-fin base covered by about 5 rows of smaller ctenoid scales; proximal part of upper- and lowermost caudal-fin rays with small weakly ctenoid scales, grading to cycloid scales distally. Pectoral-fin base with ctenoid scales anteriorly, changing to cycloid ones closer to rays. No basal scaly sheath along dorsal- and analfin bases. Small cycloid scales present proximally on membrane between last spine and first 1 or 2 rays of dorsal and anal fins. Scales between pelvic-fin bases cycloid; pelvic rays with small cycloid scales proximally. Scales on ventral surface of lower jaw restricted to angular, not extending onto dentary ( Fig. 7A ). Interorbital scales mostly cycloid, extending at most to vertical at middle of orbit ( Fig. 8C ). Uppermost row of body scales along dorsal-fin base always about half size of adjacent lower body scales; tiny and irregularly spaced scales sometimes present at bases of spines.

Dorsal-fin origin above pectoral-fin base, 4 th spine (rarely 5 th) longest, 1 st spine shortest, all soft rays branched, 8 th or 9 th longest. Anal-fin origin below base of 1 st dorsal-fin soft ray, 3 rd spine longest; all soft rays branched, 5 th longest. Pectoral fin with uppermost 2 rays and lowermost ray unbranched, remaining rays branched, its posterior tip not extending beyond anal-fin origin. Pelvic-fin origin below opercular spines; all soft rays branched, 2 nd longest, its tip usually not reaching to anus. Caudal fin truncate, its upper lobe pointed and slightly longer than lower lobe; principal caudal-fin rays 9+8, upper- and lowermost rays unbranched; 1–2 segmented and at least 5 unsegmented procurrent caudal-fin rays dorsally and ventrally.

Formula for configuration of supraneural bones, neural spines and dorsal pterygiophores 0/0/0+1/2/1/1/1/1/1/1 /1/2/1/1/1–2/1–2/1/; vertebrae 10+14.

Fresh coloration. Based on colour photographs of fresh holotype, one paratype ( Fig. 1 ) and photographic records of three (including one juvenile) not retained specimens ( Fig. 2 ). Head and body red, the scales dorsally (excluding those of lateral line) intensely edged with black. Eight or nine short white sub-triangular bars arising from ventral profile and not extending beyond level of upper pectoral-fin base. Lower part of opercle, subopercle and branchiostegal rays with a yellow tinge. Blackish dashed stripe along midbody from upper corner of opercle to midcaudal-fin base in juveniles (from behind upper corner of opercle to mid-caudal peduncle in adults) composed of a series of five or six elongate dark blotches. Dorsal fin pale yellow with reddish pigment at base of spines and rays. Anal fin light red with submarginal yellow band, distal margin whitish; last rays of anal fin sometimes with alternating yellow and grey short bands. Pectoral fins with reddish base, the remainder of fin hyaline with yellowish tinge. Membrane of pelvic fins yellow with pale red spines and rays; caudal fin red basally and extending along upper and lower edges, midposterior portion of fin with several irregular rows of yellow spots on a pale grey background.

Preserved coloration. Based on all examined specimens ( Fig. 3A ). Body pale brown, head somewhat darker, mostly on upper half, including tip of upper jaw. Five or six dark dashes, each 3–5 scales long and 1–2 scales deep, in straight line from corner of opercle and below lateral line, crossing lateral line below middle of soft portion of dorsal fin and ending above lateral line at caudal-fin base; area between dark dashes dusky. Scales above dashes and on predorsal area dark-edged. Dark brown dots present proximally between 4 th and 6 th dorsal-fin spines; dorsal-fin soft rays with dark brown dots along most of their length. Anal fin usually pale. Pectoral-fin base with melanophores, usually in stellate form, that together may look like a faint brown spot on the fin’s base, and variable amount of microscopic blackish dots proximally on pectoral-fin rays. Pelvic fins pale. Caudal fin with four or five irregular, narrow bars dark brown on central rays, becoming increasingly faint toward the dorsal and ventral margins. Microscopic blackish dots present on upper jaw, mostly on premaxilla and sometimes in two or three clusters; similar dots sometimes present on maxillary flange. Lower jaw mostly pale, but scattered microscopic blackish dots and/or one cluster of such dots, usually anteriorly, sometimes present. Peritoneum, stomach and intestine pale.

Distribution. Chelidoperca myathantuni is currently known only from the Andaman Sea, off the south-eastern coast of Myanmar at depths of 101– 185 m.

Etymology. The species is named in honor of Mya Than Tun, former Director, Research and Development Division, DOF, Myanmar and WCS national coordinator (now retired), in recognition of his remarkable contribution to improving knowledge on the fisheries resources in Myanmar, and untiring dedication to the advancement of ichthyology in his country.

Comparisons. Chelidoperca myathantuni can be distinguished from C. africana , C. cerasina , C. flavolineata , C. hirundinacea , C. lecromi , C. maculicauda and C. pleurospilus by having 3 (2 full-sized plus 1 half-sized) vs. 4 (3 full-sized plus 1 half-sized) scale rows between the lateral line and the middle of the spinous dorsal-fin base. Among the species having 3 scale rows in that region, C. myathantuni is most similar to C. occipitalis in general morphology and coloration (i.e., presence of a longitudinal dashed stripe composed of five or six blackish blotches along the side of the body) but it can be readily distinguished from the latter in lacking the short, dark bands on the upper caudal-fin ray and the small dark red spots anteriorly on the soft-rayed portion of dorsal fin (both retained as dark markings in preserved specimens). It is also distinguishable from C. occipitalis in having relatively more pectoral-fin rays [16 vs. 14–16 (modally 15)]; a longer jaw [22.2–24.1 (mean 23.2) vs. 18.4–20.3 (mean 19.4) % SL]; a shorter caudal-fin length [22.7–25.7 (mean 24.4) vs. 26.9 –28.1 (mean 27.5) % SL]; a slightly smaller head length [36.6–41.8 (mean 39.7) vs. 41.3–43.2 (mean 42.2) % SL], orbit diameter [9.9–11.6 (mean 10.5) vs. 11.5–12.6 (mean 11.8) % SL] and pectoral-fin length 22.2–26.0 (mean 24.4) [vs. 26.1–26.9 (mean 26.5) % SL].

Chelidoperca myathantuni can be easily distinguished from other congeners (except C. investigatoris ) having 3 (2 full-size plus 1 half-sized) scale rows between the lateral line and spinous dorsal-fin base by the presence of a distinct blackish dashed stripe along mid-body (retained in preserved specimens). It differs from C. investigatoris in having 16 (vs. 14–15) pectoral-fin rays; 7–8 (vs. 10) predorsal scales; a smaller head, 36.6–41.8 % (vs. 45.0–46.5 %) of SL, postorbital length, 20.2–22.7 % (vs. 26.2–27.0 %) of SL and upper jaw, 17.1–18.7 % (vs. 20.1–20.2 %) of SL; enlarged caniniform teeth in the upper jaw (vs. no distinct caniniform teeth in the upper jaw); caudal fin truncate, with the upper lobe slightly elongate and pointed and the lower lobe truncate (vs. caudal fin emarginate, with both lobes slightly elongate and pointed); pectoral fin short, nearly extending to the anus (vs. pectoral fin long, extending to the anal-fin origin; upper lip fold high (vs. upper lip fold low); interorbital scales reaching to mid-orbit (vs. extending to level of posterior nostril); scales on the lower jaw ventral surface restricted to the angular (vs. extending onto the posterior portion of the dentary). Although C. investigatoris may occasionally present a darkish dashed stripe along midbody (see Fig. 2 in Bineesh et al. 2014), it usually has a longitudinal uninterrupted yellow stripe on midbody from snout tip to caudal-fin base in fresh condition which readily distinguishes it from C. myathantuni . The latter also has several irregular rows of yellow spots on the mid-posterior portion of the caudal fin (vs. caudal fin uniformly yellowish to reddish) and a reddish anal fin with yellow submarginal band (vs. anal fin transparent with narrow yellowish to reddish edge).

The only other congener sharing with C. myathantuni a longitudinal blackish dashed stripe along the side of the body in fresh condition is C. pleurospilus ( Ogino et al. 2019; Matsunuma et al. 2020; this study). However, C. myathantuni can be distinguished from the latter species in having 3 (2 full-size plus 1 half-sized) vs. 4 (3 full-sized plus 1 half-sized) scale rows between the lateral line and middle of the spinous dorsal-fin base. Furthermore, C. myathantuni has relatively more pectoral-fin rays [16 vs. 15–16 (modally 15)]. In pigmentation, C. myathantuni differs from C. pleurospilus in having the soft portion of the dorsal fin with reddish spots mostly restricted to the base of rays (vs. two or three rows of distinct dark red elongate spots on rays) and the scales on dorsum intensely black-edged (vs. only lightly black-edged).

Remarks. Most specimens have lost many of their scales, more often those on the lower part of the body, the predorsal area, the cheek and on the fins. The cheek scale count is of the large scales between the preopercular ridge and the eye, but there are 1–3 small scales between the edge and ridge covering the preopercular sensory canal. In most specimens the small scales on the dorsal- and anal-fin rays are limited to the area between the last spine and first soft ray, but in some of the largest specimens scales are also present between the first two soft rays of these fins. Also, in most specimens there are no scales along the uppermost caudal-fin rays other those of the transverse series that covers the fin’s base. The majority of the specimens have 18–20 circumpeduncular scales, and one has 16 scales. Because the skin of the predorsal and temporal areas and the cheek was mostly damaged it was impossible to describe details of the preopercular, temporal and supratemporal sensory canals. However, in some specimens we were able to observe some tiny pores, single or paired, the latter two canals.

In preservative, colour variation in the pectoral fin includes differences between the two fins of the same fish. In the larger specimen small clusters of dark brown dots are present basally on the anal fin membrane, and also along part of the posterior rays. The dark areas of the middle caudal-fin rays look like an extension of the lateral body stripe, but there is usually a clear, unpigmented space between the last dark dash of the body stripe and the first dark bar of the caudal fin.

Figures

FIGURE 1. Fresh specimens of Chelidoperca myathantuni collected off Tanintharyi Coast, Myanmar: A. SAIAB 203716, holotype, 114.2 mm SL (photo by P.N. Psomadakis); B. SAIAB 203723, paratype, 110.9 mm SL (photo by O. Alvheim).

FIGURE 2. Images of fresh and subsequently discarded specimens of Chelidoperca myathantuni collected off Tanintharyi Coast, Myanmar (photos by O. Alvheim): A. 150 mm TL; B. 145 mm TL; C. 62 mm TL.

FIGURE 3. Preserved holotypes: A. Chelidoperca myathantuni, SAIAB 203716, 114.2 mm SL; and B. Chelidoperca flavimacula, SAIAB 209601, 69.5 mm SL, both collected off Tanintharyi Coast, Myanmar (photos by N. Mazungula).

FIGURE 5. Dorsolateral view of dorsal portion of body showing scale rows between lateral line and base of spinous dorsal fin (photos by N. Mazungula): A. Chelidoperca myathantuni, SAIAB 203716, holotype, 114.2 mm SL, and B. Chelidoperca flavimacula, SAIAB 209601, holotype, 69.5 mm SL. Red-outlined and blue-outlined scales indicate full-sized and half-sized scales, respectively.

FIGURE 6. Lateral view of posterior portion of maxilla showing condition of skin fold (photos by O. Gon): A. Chelidoperca myathantuni, SAIAB 203716, holotype, 114.2 mm SL, and B. Chelidoperca flavimacula SAIAB 209601, holotype, 69.5 mm SL. Arrows indicate upper edge of skin fold.

FIGURE 7. Ventral view of head showing scale condition (photos by O. Gon): A. Chelidoperca myathantuni, SAIAB 203716, holotype, 114.2 mm SL, and B. Chelidoperca flavimacula, SAIAB 209601, holotype, 69.5 mm SL.

FIGURE 8. Dorsal view of head showing scale condition (photos by O. Gon): A. Chelidoperca myathantuni SAIAB 203716, holotype, 114.2 mm SL, and B. Chelidoperca flavimacula, SAIAB 209601, holotype, 69.5 mm SL.