Pempheris bexillon, Mooi & Randall, 2014

Mooi, Randall D. & Randall, John E., 2014, Pempheris bexillon, a new species of sweeper (Teleostei: Pempheridae) from the Western Indian Ocean, Zootaxa 3780 (2), pp. 388-398 : 391-397

Pempheris bexillon new species

( Figures 1 , 2 ; Tables 3–7 )

Holotype. SAIAB 30861 , male, 129 mm, Comoro Islands, Grande Comore, 0.5 km north of the Coelacanth Hotel , 11.8167°S, 43.0167°E, 50–100 m offshore, volcanic rock and coral reef with caves and ledges, 5–10 m, rotenone, P.C. Heemstra, M. Smale, and J. Wright, Oct. 26, 1986.

Paratypes (11 specimens). BPBM 41165, 122 mm, same data as holotype ; CAS 33012, male, 121 mm, Grande Comore, rock reef in front of Hotel Coelacanth , rotenone, J.E. McCosker & M.D. Lagios, Mar. 1, 1975 ; CAS 33403, 8 : 119–141 mm, Grande Comore, N’Gouni Reef, about ½ km north of Iconi , surge channel at far end of small cove, outgoing tide, rotenone, J.E. McCosker, S. Mead, D. Powell, & J. Breeden, Feb. 1975 ; USNM 402278 , male, 123 mm, Comoro Islands, NW of Anjouan, 12°10’S, 44°23’E, cave in coral reef, 0–10 m, ichthyocide, Te Vega Cruise 4 , R. Bolin et al., Aug. 21, 1964 .

Other material (12 specimens). SAIAB 68413 , 2 : 140–151 mm, Mascarene Islands, Rodrigues, Grand Baie , 19.6503°S, 63.4403°E, reef, 5–10 m, ichthyocide, P.C. & E. Heemstra, M. Smale, and J. Wright, Oct. 13, 2001 ; USNM 343783, 155 mm, Mascarene Islands, Mauritius, west coast, Baie de La Petite Rivière, southwest of Albion Fisheries Research Centre , 10–11 m, P.C. Heemstra, A.C. Gill, D.G. Smith, & M.J. Smale, Apr. 28, 1995 ; USNM 343808 , 3 : 127–148 mm, Agaléga Islands, North Island , about half mile southwest of tip, 10°19’S, 56°35’E, 0–8 m rotenone , V.G. Springer , T.H. Fraser , C.L. Smith et al., Apr. 17, 1976 ; USNM 344241 , 4 : 140–145 mm, Mascarene Islands, Cargados Carajos Bank, Raphael Island , 16.43°S 59.60°E, 100 yds off west side in coral patch in surge channel, 0–8m, rotenone , T.H. Fraser , V.G. Springer , C.L. Smith et al., Apr. 2, 1976 ; MPM uncatalogued, 2: 132– 133 mm, Madagascar, Bassas da India (21.5°S 39.7°E), south side of atoll, low tide gulley on reef top, rotenone, S. Chater, June 30, 1991 .

Diagnosis. A species of Pempheris that is unique in having a yellow or yellowish dorsal fin with a black, distal margin along its full length, broadest on anterior rays (pupil-diameter width) and gradually narrowing posteriorly, the last ray with only a black tip. It can also be differentiated from congeners by the combination of the following characters: large, deciduous cycloid scales on the flank; dark, oblong spot on the pectoral-fin base; anal fin with a dark margin along its length; segmented anal-fin rays 38–45; lateral-line scales 56–65; and total gill rakers on the first arch 31–35.

Description. Dorsal rays VI,9 (VI,9–10), the spines slender, all segmented rays branched; anal rays III,41 (38– 45), the spines stout, all segmented rays branched; pectoral rays 17 (16–19), the first rudimentary, second unbranched, remaining rays branched; pelvic rays I,5; principal caudal rays 9+8, the median 15 branched; upper + lower procurrent caudal rays 5 + 5 (4–5 + 3–5), the most posterior of each segmented distally; lateral-line scales 59 (56–65) to base of caudal fin, pored scales continuing to end of fin; gill rakers 9 + 24 = 33 (8–10 + 22–25 = 31–35); branchiostegal rays 7; vertebrae 25.

Body moderately deep, the depth 2.3 (2.2–2.4) in SL, and compressed, the width 3.0 (2.45–3.05) in body depth; head length 3.6 (3.5–3.6) in SL; dorsal profile of head smoothly convex; snout short 4.5 (4.0–4.6) in HL; eye relatively small, the orbit diameter 2.3 (2.25–2.35) in HL; interorbital slightly convex, the width 3.2 (3.15–3.3) in HL; caudal-peduncle depth 2.9 (2.95–3.1) in HL; caudal-peduncle length 3.8 (3.3–3.9) in HL.

Mouth strongly oblique, forming an angle of about 60° to horizontal axis of head and body, the slender lower jaw slightly protruding when mouth fully closed; maxilla slender anteriorly, expanding posteriorly to a width twothirds to three-fourths pupil diameter, usually reaching slightly posterior to a vertical through center of eye; upper and lower margins of maxilla inwardly curved, the posterior edge straight with rounded corners; very small, sharp, incurved teeth in two irregular rows anteriorly in upper jaw, narrowing to a single row posteriorly; teeth on each side of nodular symphysis of lower jaw in a patch with at most six irregular rows of small teeth, the outer one or two rows sharply nodular, the inner three or four rows strongly recurved and narrowly sharp; teeth to side of lower jaw narrowing to two rows for most of length of jaw; all teeth of upper jaw exposed when mouth fully closed, but none of lower jaw; vomer with an expanded V-shaped patch of very small nodular teeth in three to four irregular rows; palatines with a long narrow patch of very small, medially curved teeth in three to four irregular rows anteriorly, narrowing to one or two rows posteriorly; tongue narrowly triangular, the upper surface with small papillae; gill rakers long, the longest gill filaments three-fourths length of longest gill raker.

Gill opening extending dorsally nearly to level of upper edge of orbit, and anteriorly nearly to a vertical at anterior edge of orbit. Opercular membrane ending posteriorly in a obtuse angle; margin of preopercle free only ventrally with two flat spines, the dorsoposterior spine acutely triangular, 2 mm long in holotype, separated by 3 mm from end of lower, asymmetrical, more rounded spine; a slight ridge midventrally on anterior two-thirds of chest.

Anterior and posterior nostrils in front of dorsal edge of pupil, one-third distance to median front of upper lip, the apertures vertically oval and subequal, separated by a septum nearly equal to nostril width; anterior nostril with a membranous flap on posterior edge that just reaches edge of posterior nostril when laid back.

Scales thin, deciduous, and cycloid, except finely ctenoid in posterior interorbital, on nape, dorsally on body posterior to dorsal fin and above lateral line; also ctenoid on chest, strongest ventrally, except a naked vertical zone directly ventral to base of pectoral fin; small scales on anal fin extending more than half way to margin and nearly half way to margin on caudal fin (farthest on membranes). The flank scales are in two layers, the outer layer larger and very deciduous. The lateral-line scales are in the second layer, but not completed covered (the narrow middle zone of the scale bearing the sensory canal and pore remains exposed).

Origin of dorsal fin in vertical alignment with rear base of pectoral fin, the predorsal length 2.75 (2.65–2.75) in SL; dorsal-fin base 4.95 (5.1–5.55) in SL; first dorsal spine short, 4.05 (3.2–4.1) in HL; sixth dorsal spine longest, 1.2 (1.2–1.25) in HL; first or second dorsal segmented rays longest, 1.05 (1.05–1.1) in HL; origin of anal fin below middle of dorsal fin, the preanal length 1.95 (1.9–2.0) in SL; anal-fin base 1.85 (1.8–1.85) in SL; first anal spine 6.3 (5.2–8.1) in HL; third anal spine 2.25 (2.4–2.45) in HL; longest anal segmented ray 1.55 (1.6–1.9) in HL; caudal fin length 4.0 (3.5–4.1) in SL; caudal concavity 6.6 (4.35–7.6) in HL; second or third branched pectoral ray usually longest, 3.55 (3.45–3.85) in SL; origin of pelvic fins below rear base of pectoral fins, the prepelvic length 2.65 (2.65–2.75) in SL; pelvic spine 2.25 (2.0–2.15) in HL; pelvic-fin length 1.55 (1.55–1.6) in HL.

Color of holotype in alcohol brown, the edges of scales narrowly pale yellowish; lateral line whitish; iris dark bluish gray, pupil pale yellowish, and lens dark orange-brown; dorsal fin with translucent greenish membranes, orange-yellow rays, and a black outer border on segmented-ray portion of fin, wide anteriorly (one-fourth fin length), progressively narrower posteriorly; scaled basal part of dorsal fin darker brown than body; anal fin with a dark brown band at base, a broad middle translucent zone and a blackish border; caudal fin dark brown on basal half, the rays pale yellow in outer half of this zone, followed by a zone about one-fourth length of fin with rays brownish-yellow and membranes translucent pale yellow; outer fourth of fin black, the demarcation of black and yellow paralleling incurved posterior margin of fin; upper and lower edges of caudal fin narrowly dark brown; pectoral fins yellow with a semicircular black spot as wide as pupil at base of fin; pelvic fins brownish yellow.

Color when fresh silvery with iridescence, the scale edges brown; dorsal fin lemon-yellow or merely yellowish with a black outer margin on segmented-ray portion, broadest on anterior rays and gradually narrower posteriorly; anal and caudal fins with a broad middle translucent zone, blackish margins, and broadly blackish at base ( Figs. 1 and 2 ). We are not aware of any underwater photographs.

Etymology. The species name bexillon is from the Greek meaning banner or flag, in reference to the bright yellow and black dorsal fin.

Distribution and habitat. Pempheris bexillon has been found in the Mozambique Channel (Bassas da India, Anjouan, Grande Comore) and on or near the Mascarene Plateau (Agaléga Islands, Cargados Carajos, Mauritius, and Rodrigues). Collections were made with ichthyocide on coral or rocky reefs at depths less than 10 m in areas with ledges, caves, and surge channels.

Comparisons. Most species of Pempheris have some dark markings on the dorsal fin, but this is either restricted to a narrow anterior margin or is a distal blotch restricted to the first four or five segmented rays; occasionally the dark margin and distal blotch occur in tandem ( Table 2 ). Pempheris bexillon is unusual in having a dorsal fin with a black, distal margin along its full length with the remainder of the fin yellow. Only one other species, P. flavicycla Randall et al. 2013 from the Red Sea, northern Western Indian Ocean, and eastward to Indonesia, has occasional specimens that have a dorsal-fin color approaching that of P. bexillon . The distal margin of the dorsal can be black almost to the penultimate dorsal ray, but the remainder of the fin is not yellow ( Randall et al. 2013, figs. 3–4); in more typical specimens the dorsal fin has only a dark anterior margin and black distal blotch on fin-rays 1–4 ( Randall et al. 2013, figs. 5–9). In addition, when a dorsal-fin marginal band is present in P. flavicycla , it is less sharply defined; the eye of this species also has a distinctive yellow iris ring around the pupil. Meristic data are very similar between these two species.

Among remaining described species of deciduous cycloid-scaled Pempheris , only two share the simultaneous presence of a distinct, dark spot on the base of the pectoral fin and dark, distal margin along the length of the anal fin: P. otaitensis Cuvier 1831 and P. ufuagari Koeda et al. 2013 ( Table 2 ). Pempheris otaitensis differs from P. bexillon in having a higher lateral-line scale count (> 70) ( Table 1 ) and has not been reliably recorded in the Western Indian Ocean; P. ufuagari has lower gill-raker counts (<31) and is known only from the Daito and Ogasawara Islands southeast of Japan ( Koeda et al. 2013).

Excluding P. flavicycla , the most similar species using meristics alone is P. nesogallica Cuvier 1831 described from Mauritius; both lateral-line scale counts and high gill-raker counts overlap ( Table 1 ). The present condition of the type material of P. nesogallica suggests that the specimens might have a basal pectoral spot as there is some duskiness visible, but the dorsal fin exhibits only a large, distal blotch on anterior rays and there is no trace of a dark, distal margin on the anal fin ( Figs. 3 , 4 ). The original description ( Cuvier 1831: 506) is somewhat vague regarding color in that it begins by noting P. nesogallica resembles P. vanicolensis in having black on the tip of the dorsal fin, but remains silent on the presence or absence of either a pectoral-fin basal spot or black margin on the anal fin. However, Cuvier (1831) seems consistent in mentioning these features when they occur in other species and emphasizes that the dark pectoral spot is very noticeable and remains in both wet and taxidermied specimens (p. 305: “…la tache très-noire de la base de la pectorale, qui est si remarquable et se conserve dans la liqueur et dans le sec”). Given this emphasis, it seems reasonable to assume that Cuvier would have made special note of a dark pectoral-fin base spot and dark distal margin on the anal fin in P. nesogallica if they had been present. Having neither of these features, nor a dorsal fin with a black distal margin over its entire length, would distinguish P. nesogallica from P. bexillon .

Remarks. The cycloid-scaled species of the genus Pempheris have proven a challenge taxonomically. It is enormously difficult to assign original names to modern specimens because most of the type material is in relatively poor condition and the descriptions are generally brief and do not take note of features considered important for identification today. Traditional meristics can be useful in dividing taxa into species groups, but tend not to be informative at the species level because they are at either of the extremes of being too variable (e.g., analfin ray and lateral-line scale counts) or too conservative (e.g. pectoral-fin ray and dorsal-fin ray counts). Gill-raker counts on the first arch are useful, but have not been reported consistently. Color patterns can be useful, but are not always maintained in preserved specimens. As a result, most faunal compilations are not reliable for determining species distributions. Tables 1 and 2 provide summaries of some of the meristic and color features of the types of nominal species of Indo-Pacific cycloid-scaled species. This will prove to be a useful reference for future taxonomic work. Discovering a species such as P. bexillon that exhibits both meristic and color characteristics that are so clearly diagnostic is an exception within this genus.

Figures

FIGURE 1. Left lateral view of the holotype of Pempheris bexillon n. sp. shortly after capture, SAIAB 30861, male, 129 mm SL, 0.5 km north of the Coelacanth Hotel, Grande Comore, Comoro Islands. Photo by P.C. Heemstra, used with permission.

FIGURE 2. Left lateral view of Pempheris bexillon Mooi & Randall n. sp. shortly after capture, SAIAB 68413, 140 mm SL, Grand Baie, Rodrigues, Mascarene Islands. Photo by P.C. Heemstra, used with permission.

FIGURE 3. Left lateral view of a syntype of Pempheris nesogallica Cuvier, MNHN A.222, 138 mm SL, Mauritius (Isle de France), Dussumier? (collector after Bauchot 1963).

FIGURE 4. Left lateral view of a syntype of Pempheris nesogallica Cuvier, MNHN B.2514, 127 mm SL, Mauritius (Isle de France), Dussumier? (collector after Bauchot 1963).