Plectranthias alcocki, Bineesh, K. K., Akhilesh, K. V., Gopalakrishnan, A. & Jena, J. K., 2014

Bineesh, K. K., Akhilesh, K. V., Gopalakrishnan, A. & Jena, J. K., 2014, Plectranthias alcocki, a new anthiine fish species (Perciformes: Serranidae) from the Arabian Sea, off southwest India, Zootaxa 3785 (3), pp. 490-496 : 492-496

Plectranthias alcocki n. sp. Bineesh, Gopalakrishnan and Jena

Figures 2–4 , Table 1 .

Holotype. CMFRIGB.31.139.30.10, 72.2 mm SL, off Kollam, Kerala coast, India, southeastern Arabian Sea, 180- 320 m depth, shrimp trawl, collected by K.K. Bineesh and K.V. Akhilesh, 22 August, 2012.

Paratype. CMFRIGB.31.139.30.10.1, 63.7 mm SL. Same data as holotype.

Diagnosis. A species of Plectranthias with the following combination of characters: dorsal-fin rays X,15; anal-fin rays III,7; pectoral-fin rays 14; pelvic-fin rays I,5; lateral-line complete, the pored scales 28; scales above lateral line to origin of dorsal fin 1; scales dorsally on head extending to posterior nostrils; no scales on maxilla or chin; gill-rakers 5 + 11 (2 + 7 developed); circumpeduncular scales 10; fourth dorsal spine longest, 2.8 (2.6) in HL, body depth 34.4 (35)% SL; head length 46 (49.8)% SL; orbit diameter 8.6 in SL; margin of preopercle finely serrate, the serrae 33 (28), ventral edge without antrorse spines; dorsal fin slightly notched and continuous, with longest dorsal soft ray (second) 2.4 (2.7) in HL; first anal-fin spine 4.9 (5.6) in HL, second anal spine 2.2 (2.6) in HL; the dorsal fin with a black blotch at base of fourth to eighth spines, one at base of the last three spines, and two at base of soft portion of fin, the dark pigment extending onto adjacent body.

Description. Dorsal-fin rays X,15 (all rays branched, the last to base); anal-fin rays III,7 (all rays branched); pectoral-fin rays 14 (both sides counted; all unbranched); pelvic-fin rays I,5; 4th dorsal spine longest 16.5 (18.8)% SL, 2.8 (2.6) in HL; short cirrus behind tips of 3rd spine; caudal-fin rays broken, but possibly slightly emarginate, principal rays 19, branched rays 17; lateral line complete, not interrupted with 28 pored scales; one row of scales above lateral-line to origin of dorsal fin; circumpeduncular scales 10; gill rakers 5 + 11 (2 + 7 developed), first lower-limb gill raker on first gill arch adjacent to raker at angle longest, its length one-half orbit diameter; branchiostegal rays 7.

Body moderately elongate, depth 1.3 (1.4) in HL, 34.4 (35)% SL; and compressed, the width 2.1 (2.2) in body depth; head pointed, the lower jaw slightly projecting; dorsal profile of head smoothly convex; head length 46 (49.8)% SL, 2.2 (2) in SL; snout length 4.9 (5.2) in head; orbit diameter 4 (4.3) in HL; interorbital space flat, the least bony width 11.5 (10.8) in HL; least depth of caudal peduncle 3.6 (4.3) in HL; caudal peduncle length 2.3 (2.4) in HL.

Opercle with three prominent flat spines posteriorly, the middle spine largest and terminating most posteriorly, curving slightly upward, its sharp tip at level of middle of pupil, closer to lower than upper spine; upper spine terminating most anteriorly and most pointed; lower and middle spine very acute and sharp; margin of Preopercle finely serrate, serrae 33 (28), ventral edge without antrorse spines; subopercle and interopercle smooth; opercular flap well-developed and angling upward in alignment with middle opercular spine. No scales on maxilla, snout, sub orbital or interobital.

Mouth terminal, oblique and large; the maxilla extending posteriorly to a vertical through posterior third of orbit, the upper-jaw length 2.2 (2.4) in head length. Mouth with an incurved canine tooth on each side at front of upper jaw separated by a symphysial gap without teeth; a band of villiform teeth in upper jaw that broadens anteriorly; posterior half of lower jaw with a narrow band of medially depressible conical teeth in three rows, those of outer row very small, those of inner row largest; a fixed recurved canine tooth in outer row at mid-side of lower jaw; tooth bands on lower jaws almost contiguous; vomer with villiform teeth in two to three irregular rows; palatines with a narrow band of villiform teeth in two to three irregular rows. Tongue narrowly triangular with a slightly rounded tip.

Dorsal fin continuous and slightly notched; origin of dorsal fin over second lateral-line scale; first dorsal spine 7.9 in HL; second dorsal spine nearly twice as long as first, 4.3 in HL; fourth dorsal spine longest, 2.8 (2.6) in HL, 16.5(18.8)% SL, last dorsal spine 4.9 (5.8) in HL; second dorsal-fin soft ray longest, 2.4 (2.7) in HL; origin of anal fin below base of second dorsal-fin soft ray: first anal spine 4.9 (5.6) in HL; second anal spine 2.2 (2.6) in HL, longer than third spine; third anal spine 3 (3.5) in HL; fourth anal soft ray longest, 2 (2.4) in HL; caudal fin broken in both specimens but seems to have been emarginate; pectoral fin 1.3 in HL (longest rays ninth and tenth), reaching to second anal soft ray in vertical; origin of pelvic fins slightly anterior to vertical line from upper end of gill opening and pectorals; pelvic fins reaching 1–4 mm before anus, pelvic fin length 2 in HL (second ray longest).

Colouration. When collected, mainly red posterior to an oblique demarcation from mid nape to origin of anal fin, then brown anteriorly, the head suffused with orange-yellow anteriorly; body with blackish pigment on the scales increasingly darker dorsally and posteriorly, more blackish than red on posterior half of caudal peduncle; a black spot posteriorly on opercle, and a dusky spot ventrally on abdomen; fins translucent yellow, the dorsal with a black blotch at base of fourth to eighth spines, one at base of the last three spines, and two at base of soft portion of fin, the dark pigment extending onto adjacent body ( Fig. 2 ). Colour in formalin pale with traces of black blotches on the body ( Figs. 3 & 4 ).

Distribution. Presently known only from off the southwest coast of India in the Arabian Sea, at depths of 180– 320 m.

Etymology. The species is named in honour of W. Alcock, in recognition of his contribution to the taxonomy of deep-sea fauna of Indian seas. Proposed English common name: Alcock’s deep-reef basslet.

Comparisons. Plectranthias alcocki n. sp. can be distinguished from all other species of the genus Plectranthias , except P. maugei Randall, 1980 and P. foresti Fourmanoir, 1977 , by its unique colour pattern, consisting of dorsal fin with a black blotch at base of fourth to eighth spines, one at base of the last three spines, and two at base of soft portion of fin, the dark pigment extending onto adjacent body and several morphometric characters ( Randall, 1980; Heemstra & Randall, 2009). Amongst the Indian Ocean Plectranthias , P. alcocki n. sp. is readily distinguished from P. maugei in having 14 pectoral-fin rays (13 rays in P. maugei ), head length 46.0– 49.8% SL (vs 42.1–43.1), eye diameter 4-4.3 in head length (vs 3.5–3.6), caudal peduncle length 2.3–2.4 in head length (vs 3.3–3.6), circumpeduncular scales 10 (vs 14 in P. maugei ) ( Randall, 1980; Heemstra & Randall, 2008).

Plectranthias alcocki n. sp. can be distinguished from P. intermedius ( Kotthaus, 1973) by having a slightly notched fin margin before soft-rayed part (vs fin margin distinctly notched before soft-rayed part); dorsal-fin rays X, 15 (vs X, 17); pectoral fins 14 rays (vs 14 or 15); greatest body depth 1.3–1.4 (vs 2.6) in head length; large eye, 3.9–4.3 in head length (vs 3.0); lateral-line with 28 pored scales (vs 31–34 in P. intermedius ) (Heemstra & Randall, 2009)

Plectranthias alcocki is differentiated from P. inermis Randall, 1980 in having X, 15 (vs X,16 to 20) dorsal-fin rays, 4th dorsal spine longest (vs 3rd spine longest), pectoral-fin rays 14 (vs 13 rays), pelvic fin length 2 in head length (vs 1.6–1.8), head length 2.0– 2.2 in standard length (vs 2.2–2.4), inter orbital length 10.8–11.5 in HL (vs 11– 14) and serrated preopercle (smooth) ( Heemstra & Randall, 2008).

Plectranthias alcocki n. sp. is differentiated from P. foresti Fourmanoir, 1977 in having 14 pectoral-fin rays (13 rays in P. f ore s t i), gill rakers 5 + 11 (4–5 + 11–13), body depth 2.9 (vs 2.6–2.8) in SL, fourth spine 2.6–2.8 in HL (vs 2.4–2.5), pectoral fin 2.6–2.9 in SL (2.5–2.7), pelvic fin length two in head length (1.7–1.85) ( Randall, 1980).

Plectranthias alcocki n. sp. and P. vexillarius Randall, 1980 share the same complete lateral-line with 28 pored scales, margin of preopercle finely serrate with 33 serrae but P. alcocki can be distinguished from P. vexillarius by a large eye diameter 3.9–4.3 (vs 3.0– 3.8 in head length) and presence of black blotch at base of fourth to eighth spines, one at base of the last three spines, and two at base of soft portion of fin vs 4 irregular rows of large brown blotches. P. alcocki is further distinguished from P. vexillarius in having the 4th dorsal spine longest (vs 3rd) and dorsal-fin rays X, 15 (vs X, 17) (Heemstra & Randall, 2009).

Plectranthias winniensis Tyler, 1966 differs from Plectranthias alcocki n. sp. in certain meristic counts and morphometrics such as: dorsal fin rays (X, 15–17), deeply notched dorsal fins, pectoral rays 16–18, gill raker count 4–6 + 11–15, pelvic fin length 1.5–1.8 in HL, orbit diameter 2.7–3.0 in HL and its colour pattern (having a spot in the base of last three anal rays) and absence of cirri on dorsal-fin spines (Heemstra & Randall, 2009).

Plectranthias alcocki and P. nanus Randall, 1980 also share similar characters, including the same pectoral-fin ray and gill-raker counts, single row of large scales between 5th dorsal spine and lateral line, 4th spine longest in both species and maxilla reaching a vertical at rear edge of eye. They differ in dorsal soft-ray count (15 for P. alcocki , 16 for P. nanus ), lateral line count (28 for P. alcocki , 16–22 for P. nanus and incomplete), antrorse-spine count (no antrorse spine in P. alcocki , 2 spines in P. nanus ) and very large eye in P. alcocki (4.0– 4.3 in HL), compared with P. nanus (3.4–4.0 in HL) ( Randall, 1980; Heemstra & Randall, 2009).

Figures

FIGURE 2. Holotype of Plectranthias alcocki n. sp., CMFRI GB. 31.139.30.10, 72.2 mm SL, off Kollam, Kerala coast, India.

FIGURE 3. Lateral view of Plectranthias alcocki n. sp., holotype CMFRIGB. 31.139.30.10 72.2 mm SL off Kollam, Kerala coast, India, after preservation.

FIGURE 4. Lateral view of Plectranthias alcocki n. sp., Paratype CMFRIGB. 31.139.30.10.1, 63.7 mm SL, off Kollam, Kerala coast, India, after preservation.

Tables

TABLE 1. Proportional measurements of holotype and paratype of Plectranthias alcocki sp. nov. expressed as a percentage of standard length.

Measurements	Holotype GB.31.139.30.10	Paratype GB.31.139.30.10.1
Standard length (mm) Head length Snout length	72.2 46.0 9.5	63.7 49.8 9.6
Eye diameter Post orbital length Upper jaw length	11.6 26.3 20.7	11.6 29.5 20.7
Maxillary width Interorbital width	6.4 4.0	6.8 4.6
Body depth Body width Pre-dorsal length Pre-anal length	34.4 16.2 39.2 70.5	35.0 15.8 41.8 68.1
Pre-pelvic length Dorsal-fin base length	37.3 52.3	37.3 53.9
Anal-fin base length Anal fin length Pelvic fin length Pectoral fin length	15.6 30.0 23.1 34.9	16.3 broken 25.3 38.4
Pre-pectoral length Caudal peduncle depth	40.3 12.8	42.6 11.5
Caudal peduncle length First anal spine length Second anal spine length Third anal spine length	19.7 9.5 20.8 15.4	20.8 8.8 19.4 14.3
First dorsal spine length Second dorsal spine length	5.8 10.8	6.3 11.5
Third dorsal spine length Fourth dorsal spine length Fifth dorsal spine length Tenth dorsal spine length	16.1 16.5 14.8 9.4	16.0 18.8 18.0 8.7
Longest dorsal spine length Longest dorsal soft ray length	16.4 18.8	18.8 18.3
Longest anal soft ray length Pelvic spine length Counts Dorsal-fin rays	23.3 12.8 X, 15	20.9 14.6
Pectoral-fin rays Anal-fin rays	14 III, 7
Pelvic-fin rays Gill rakers (upper) Gill rakers (lower) Lateral line scales	I, 6 5 11 28