Plectranthias polygonius, Shepherd & Phelps & Pinheiro & Rocha & Rocha, 2020

Shepherd, Bart, Phelps, Tyler A. Y., Pinheiro, Hudson T., Rocha, Claudia R. & Rocha, Luiz A., 2020, Two new species of Plectranthias (Teleostei, Serranidae, Anthiadinae) from mesophotic coral ecosystems in the tropical Central Pacific, ZooKeys 941, pp. 145-161 : 145

Plectranthias polygonius sp. nov. Figures 1 , 2A , Table 1 Polygon Perchlet

Type locality.

Tahiti, French Polynesia.

Holotype.

CAS 247193, field code: HTP906, GenBank MN922331. 29.5 mm SL, Tahiti, French Polynesia, 17°29'27"S, 149°28'01"W, depth of collection 105 m, collected with hand nets by B Shepherd, HT Pinheiro, TAY Phelps, MV Bell, and LA Rocha, 03 March 2019.

Paratype.

USNM 445722, field code: HTP942, GenBank MN922330. 32.3 mm SL, Maloelap Atoll, Republic of the Marshall Islands, 8°37'42"N, 170°59'58"E, depth of collection 120 m, collected with hand nets by HT Pinheiro, TAY Phelps, MV Bell, and LA Rocha, 13 August 2019.

Diagnosis.

Plectranthias polygonius sp. nov. can be distinguished from all of its congeners by live coloration, in particular the two rows of orange rhomboid-shaped polygons on the lateral part of the body and an elongated yellow and white third dorsal spine (Fig. 1A, D ), and by the following combination of characters: dorsal-fin rays X, 16; pectoral-fin rays 14, all unbranched; vertebrae 10+16; continuous lateral line with 27-30 tubed scales; circumpeduncular scales 10 or 11; absence of antrorse spines on the preopercle.

Description.

Proportional measurements for the type specimens are presented in Table 1 . Dorsal rays X, 16, the last soft ray branched to base and counted as one; first dorsal spine short, 18.0 in SL (15.8); third dorsal spine longest, 1.7 in HL (1.6) with flag-like extension; dorsal-fin base length 2.1 in SL (1.9); anal-fin rays III, 7, last soft ray branched to base and counted as one; anal-fin base length 6.3 in SL (6.5); second anal spine longest and stoutest at 1.6 in HL; anal-fin origin at vertical beneath fourth dorsal-fin ray; pectoral-fin rays 14, all unbranched, length 3.8 in SL (3.4); pelvic fin I, 5; pelvic-fin length 4.6 in SL (4.2); pelvic-spine length 2.0 in HL; procurrent caudal-fin rays 7+6 (6+5); principal caudal-fin rays 9+8.

Body moderately elongate, laterally compressed; depth of body 3.4 in SL (3.2); width of body 2.7 in depth (2.3); head length 3.2 in SL (3.1); snout length 3.4 in HL (3.6); bony interorbital width 1.6 in snout length (1.3); orbit diameter 2.8 in HL; post-orbital head length 4.8 in SL (4.7); least depth of caudal-peduncle 2.5 in HL; caudal peduncle length 3.6 in HL (4.0).

Scales ctenoid; lateral line complete and broadly arched over pectoral fin following body contour; 30 (27) tubed scales; scales above lateral line to origin of dorsal fin 2; scales above lateral line to base of middle dorsal spine 2; scales below lateral line to origin of anal fin 9 (10); diagonal rows of scales on cheek 5; scales on top of head extending anteriorly to vertical from anterior margin of pupil; no scales on chin, maxilla, or snout; circumpeduncular scales 10 (11); gill rakers 5+13 (6+13); vertebrae 10+16; supraneurals 3; anterior supraneural-dorsal ray-pterygiophore-neural spine interdigitation pattern: 0/0+0/2/1+1/1.

Mouth large and terminal, slightly upturned; lower jaw protrudes slightly; maxilla expanded posteriorly, extending to below the posterior edge of eye; dorsal profile of head almost straight; upper jaw with one fixed, stout canine on either side of symphysis; upper canines flanked internally by villiform band with four or five rows of depressible, smaller, sharp-tipped teeth; inner rows become progressively longer, innermost row with largest teeth; lower jaw has pair of fixed, short stout canines on either side of symphysis followed by smaller, depressible, sharp-tipped conical teeth in a villiform band of 3-5 rows; lower teeth become progressively longer on inner rows; vomer roughly V-shaped band of two rows of similarly sized, sharp-tipped, conical teeth; palatines with one row of small, sharp-tipped conical teeth; tongue small, slender, pointed, and without teeth.

Opercle with three spines, the middle spine the longest; preopercle with 14 (17) small spines (serrae) along posterior margin; antrorse spines lacking on ventral margin; interopercle with no spines; subopercle smooth, with no spines; anterior nostrils positioned halfway between snout and eye, each with a small rounded flap rising from anterior rim; posterior nostrils an elliptical opening at anterior border of orbit.

Color in life.

Body: overall white with two rows of bright orange rhomboid-shaped polygons, four to six in each row, arranged in an irregular grid along lateral midline of body; uppermost row of orange polygons proceeds from behind eye to dorsal third of caudal peduncle; lower row starts just dorsal to origin of pectoral fin and continues to ventral half of caudal peduncle; throat and belly white. Head: dorsal third of head orange and bottom two thirds pinkish white with two yellow stripes, both originating from the tip of the upper lip. The first extending horizontally across orbit, bifurcating past posterior edge of pupil to approximately edge of opercle. The second from tip of upper lip, tracing obliquely along maxilla and extending to ventral edge of preopercle. Preopercle region with a yellow triangular patch, from lower mid-orbit expanding in width to edge of preopercle with bifurcations to horizontal edge of operculum and pelvic fin bases respectively; orbit mostly orange-red; iris outlined in silver-grey to black with horizontal yellow stripe through middle of anterior portion; posterior portion of iris with two yellow stripes arising from a bifurcation of the anterior yellow stripe; pupil black. Fins: first three membranes of spinous portion of dorsal fin mostly orange with yellow highlights; third spine with yellow and white membrane; remaining membranes of spinous portion mostly yellow, with hyaline tips; yellow coloration continues on lower third of soft portion of dorsal fin, with upper two-thirds mostly hyaline; some yellow and pale orange on tips of soft dorsal and membranes of last four to five rays; caudal fin hyaline with white and orange rays; anal fin mostly yellow, with white margin; pelvic fins mostly white distally, with yellow rays proximally; pectoral fins hyaline. Living specimen photographed in the Marshall Islands exhibits more yellow coloration on head, within rhomboid-shaped polygons on lateral midline, and on first three membranes of spinous dorsal fin (Fig. 2A ).

Color in alcohol.

Light tan overall, with no visible markings.

Etymology.

Plectranthias polygonius sp. nov. is named for the orange rhomboid-shaped polygons arranged in parallel rows along the lateral midline that distinguish it from all other known species within the genus. To be treated as a noun in apposition.

Distribution and habitat.

Plectranthias polygonius sp. nov. appears to be the same species as an undescribed Plectranthias species that was photographed off Rangiroa, French Polynesia, at a depth of 65 m ( Williams et al. 2013). However, some superficial differences exist between our specimen and the one in Williams et al. (2013), including the thickness of the white lines on the upper body and the color of the iris. These may be due to individual variability. The two specimens described in this paper were collected in highly complex reefs predominantly covered by coralline algae and sponges in Tahiti (Fig. 3A ) and crevices of steep reef walls in the Marshall Islands (Fig. 3B ), indicating that this species probably has a wider Pacific distribution. All known individuals have been observed or collected at mesophotic depths, suggesting that Plectranthias polygonius sp. nov., as with most of its congeners, does not inhabit shallow coral reef habitats.

Comparisons.

The general body shape, color, and prolongation of the third dorsal-fin spine in Plectranthias polygonius sp. nov. resemble P. inermis and P. altipinnatus (Fig. 2B, C ); however, the barcode fragment of the COI gene of P. polygonius sp. nov. is not close to any published barcode sequence of Plectranthias , with approximately 15% uncorrected pairwise genetic distance from several species in the genus. Morphologically, it can easily be distinguished from P. inermis by having ten circumpeduncular scales (vs. 14 or 15 in P. inermis ); canine teeth on the lower jaw (lacking in P. inermis ); and 14-17 spines on the posterior edge of the preopercle (spines lacking in P. inermis ; feebly serrated in P. altipinnatus ). The new species differs from P. altipinnatus by having X, 16 dorsal-fin rays (X, 18 in P. altipinnatus ), a shallower body (3.2-3.4 in SL vs. 2.8 in P. altipinnatus ), smaller head (3.1-3.2 in SL vs. 2.2 in P. altipinnatus ), and a larger eye (2.8 in HL vs. 4.75 in P. altipinnatus ).

Figures

Figure 1. Plectranthias polygonius sp. nov. holotype A shortly after death B preserved C radiograph, and paratype D shortly after death E preserved F radiograph. Photographs by LA Rocha (A), A Gaisiner (B, E), J Fong (C, F), and T Sinclair-Taylor (D).

Figure 2. Plectranthias polygonius sp. nov. at Erikub Atoll, Republic of the Marshall Islands, at a depth of 120 m (A), aquarium photos of P. inermis (B), and P. altipinnatus (C). Photographs by LA Rocha (A) and YK Tea (B, C).

Figure 3. Habitat of Plectranthias polygonius sp. nov. and Plectranthias hinano sp. nov. in A Tahiti, French Polynesia, depth of approximately 100 m, and B Erikub Atoll, Republic of the Marshall Islands, depth of approximately 120 m. Photographs by LA Rocha.