Plectranthias ahiahiata, Shepherd, Bart, Phelps, Tyler, Pinheiro, Hudson T., Perez-Matus, Alejandro & Rocha, Luiz A., 2018

Shepherd, Bart, Phelps, Tyler, Pinheiro, Hudson T., Perez-Matus, Alejandro & Rocha, Luiz A., 2018, Plectranthiasahiahiata, a new species of perchlet from a mesophotic ecosystem at Rapa Nui (Easter Island) (Teleostei, Serranidae, Anthiadinae), ZooKeys 762, pp. 105-116 : 105

Plectranthias ahiahiata sp. n. Figure 1, 2, 3, Table 1 Sunset perchlet

Type locality.

Hanga Piko, Rapa Nui (Easter Island), Chile.

Holotype.

CAS244172 (Field number LAR 2644). 39.95 mm SL, GenBank accession number MH025944. Location: Hanga Piko, Rapa Nui, Chile (27°9'12"S 109°26'52"W). Collected by B. Shepherd using a hand-net, 7 March 2017 (Figure 1-3).

Comparative material.

Published morphometric and meristic data from the known eastern Pacific species, Plectranthias exsul (Anderson and Baldwin 2002), P. nazcae (Anderson 2008) and P. parini (Anderson and Randall 1991); the Atlantic species P. garrupellus Anderson and Heemstra 2012; the Western Pacific species P. anthiodes Gunther 1872, P. bennetti , P. elongatus Wu, Randall and Chen 2011, P. flammeus , P. fourmanoiri , P. jothyi Randall 1996, P. kamii , P. inermis Randall 1980, P. randalli , P. sheni Chen and Shao 2002, P. taylori Randall 1980, and P. xanthomaculatus Wu, Randall and Chen 2011 ( Yoshino 1972; Randall 1980; Randall 1996; Wu et al. 2011; Williams et al. 2013; Peristiwady et al. 2014; Allen and Walsh 2015; Tashiro and Motomura 2017); the Japanese species, P altipinnatus Katayama and Masuda 1980, P. takasei Gill, Tea and Senou 2016, and P. yamakawai Yoshino, 1972; and the Arabian species, P. alcocki Bineesh, Akhilesh, Gopalakrishnan and Jena 2014. Specimens of P. japonicus (CAS33555), P. sagamiensis (CAS235596), and P. winniensis (CAS19169).

Diagnosis.

Plectranthias ahiahiata differs from all of its congeners by the following combination of characters: dorsal rays X, 18; pectoral rays 18; longest dorsal spine the fourth; LL continuous and complete with 31 tubed scales; circumpeduncular scales 16; head length 43.3% SL; first dorsal spine 4.5% SL; third anal spine 13.7% SL; gill rakers 6+11; and in coloration: overall orange-red in color, with predominantly yellow snout, dorsal, pelvic and anal fins, a brilliant red spot outlined in white on the caudal peduncle, and four white spots on each side, following the contour of the lateral line.

Description.

Proportional measurements and morphological counts of the holotype are given in Table 1. Dorsal rays X, 18; last soft ray branched to base and counted as one; first dorsal spine very short, 4.5% SL; fourth dorsal spine longest, 15.6% SL; dorsal-fin base length 51.4% SL. Anal-fin rays III, 7; last soft ray branched to base and counted as one; anal-fin base 13.7% SL; second anal spine longest at 19.0% SL; anal-fin origin at vertical beneath fifth dorsal-fin ray; pectoral-fin rays 18; length 33.8% SL; pelvic fin I, 5; pelvic-fin length 26.5% SL; pelvic-spine length 16.5% SL; caudal fin with three dorsal and two ventral procurrent rays, two dorsal and one ventral unbranched rays, 7+7 branched rays; tubular lateral-line scales 31; vertical scale rows 30; scales above LL to origin of dorsal fin 3; scales above LL to base of middle dorsal spine 2; scales above LL to origin of anal fin 12; diagonal rows of scales on cheek 4; scales on top of head extending anteriorly to vertical from posterior margin of orbit, where two rows of mid-dorsal scales continue anteriorly to posterior margin of iris; area on top of head between eyes scaleless; no scales on chin, maxilla, or snout; circumpeduncular scales 16; caudal-peduncle length 10.4% SL; caudal-peduncle depth 12.5% SL; body moderately elongate, laterally compressed; body depth 30.8% SL; body width 16.7% SL; gill rakers 6+11; vertebrae 10+16; supraneurals 3.

Mouth large and terminal, slightly upturned; lower jaw protrudes slightly; maxilla expanded posteriorly, extending to below the posterior edge of eye; head long, length 43.3% SL; dorsal profile of head almost straight; post-orbital head length 12.9% SL; snout length 11.0% SL; orbit diameter 9.6% SL; upper jaw with a pair fixed, stout canines on either side of symphysis; inner canine larger of the pair; upper canines flanked internally by villiform band with four to eight rows of depressible, smaller, sharp-tipped teeth; inner rows become progressively longer, innermost row with largest teeth, some larger than upper canines; lower jaw has outer row of fixed, short stout canines at symphysis followed by smaller, depressible, sharp-tipped conical teeth in a villiform band of approx. four to six rows; lower teeth become progressively longer on inner rows, teeth of inner row approx. three times longer than teeth of middle rows, villiform band narrows to one row toward sides of lower jaw; two large fixed canines at midpoint on either side of lower jaw; vomer roughly V-shaped band of two rows of similarly-sized, sharp-tipped, conical teeth; palatines with two rows of small, sharp-tipped conical teeth; tongue small, narrow, pointed, and without teeth.

Scales ctenoid; lateral line complete and broadly arched over pectoral fin following body contour; 31 tubed scales, the last seven in a straight line. Opercle with three spines; preopercle with nine small spines along posterior margin and two antrorse spines on ventral margin; interopercle with one spine; subopercle smooth, with one spine; anterior nostrils positioned at middle of snout, 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 yellow, orange, and red in color; chest and belly mostly yellow, with yellow extending dorsally to just behind origin of pectoral fin; ventral-most portion of belly white; dorsal portion of body orange-red; series of two to three indistinct orange bars alternating with light pink to white interspaces on the posterior half of the body, followed by a red bar originating below the eleventh dorsal ray and continuing to the base of caudal peduncle; brilliant red spot on the caudal peduncle, approximately same diameter as orbit, outlined in white; four irregularly-shaped white spots on each side of body: first on operculum outlined with dark pink to red border, second just behind the posterior edge of the operculum and beneath the anterior portion of the lateral line and the first and second dorsal spines, third below the eighth dorsal-fin spine, and fourth just below the lateral line beneath and between the fourth and fifth soft dorsal fin rays. These white spots resemble those of P. winniensis collected at Pitcairn Island (Randall, unpublished photograph) Head: snout, throat, and maxilla mostly yellow; anterior portion of lower lip orange; three indistinct yellow stripes radiating from the anterior portion of the snout through the eye and across the operculum with two light pink to white interspaces; upper interspace extending from lower third of iris to white spot on operculum, lower interspace originating beneath orbit and extending to origin of pectoral fin along upper edge of maxilla; orange stripe originating at tip of snout proceeding across dorsal third of eye and ending at the origin of the lateral line; iris alternating yellow and white lateral stripes, separated with faint, thin red borders; edge of iris outlined in dark-grey to black; Fins: spinous portion of dorsal fin translucent yellow; dorsal spines one to six outlined in orange-red along entire length; dorsal spines seven to ten mostly yellow, outlined with red primarily on spine tips; dorsal rays orange-red; lower third of soft dorsal fin mostly yellow, upper two-thirds translucent; caudal-fin membranes translucent with orange-red fin rays; pelvic and anal fins mostly yellow with white and translucent fin rays; pectoral fins translucent yellow with rays outlined in red; base of pectoral fins bright yellow.

Color in alcohol.

Light tan overall, with no visible markings (Figure 2).

Etymology.

Plectranthias ahiahiata is given a Rapa Nui name; the phrase ahiahi-ata means "the last moments of light before nightfall." The species was given this name because the colors of the fish remind us of the beautiful Rapa Nui sunsets. To be treated as a noun in apposition.

Distribution and habitat.

Plectranthias ahiahiata is currently only known to occur at Rapa Nui (Easter Island). This fish was collected with hand nets at a depth of 83 m in a rocky patch reef surrounded by a large sandy area, and transported to the surface alive in a perforated plastic jar.