Plectranthias bennetti Allen & Walsh

Gill, Anthony C., Pogonoski, John J., Moore, Glenn I. & Johnson, Jeffrey W., 2021, Review of Australian species of Plectranthias Bleeker and Selenanthias Tanaka (Teleostei: Serranidae: Anthiadinae), with descriptions of four new species, Zootaxa 4918 (1), pp. 1-116 : 46-47

Plectranthias bennetti Allen & Walsh

Figures 7 , 14 ; Tables 1–16, 22

Common name: Bennett’s Perchlet

Plectranthias bennetti Allen & Walsh 2015: 83 , figs 1–4 (type locality, Holmes Reef, Coral Sea).— Anderson 2018: 26 (checklist). — Parenti & Randall 2020: 24 (checklist).

Diagnosis. The following combination of characters distinguishes P. bennetti from congeners: dorsal rays X,15, fourth spine longest; pectoral rays 13, all unbranched; lateral line complete, with 29–30 scales; lower part of preopercle with three enlarged antrorse spines; scales on head extending anteriorly to point varying from mid-interorbital to anterior part of interorbital, but well short of posterior nostrils; no scales on snout, maxilla, infraorbitals, mandibles or chin.

Remarks. Allen & Walsh (2015) described P. bennetti on the basis of the holotype collected by Cairns Marine aquarium fish collector T. Bennett at Holmes Reef, Coral Sea. They noted that the collector had collected one other specimen of the species, but it had been sold to the Japanese aquarium trade. However, we located an additional specimen (WAM P.33842-001), which had been collected at Holmes Reef by T. Bennett in 2012 but had been misidentified as P. winniensis . The specimen has damaged tips to median and pectoral-fin ray rays and some missing scales on the right side but is otherwise in good condition ( Figure 14A ). Two additional specimens were available for study, both collected by T. Bennett at Holmes Reef subsequent to the original description. The three specimens agree well with Allen & Walsh’s (2015) original description of P. bennetti in all salient features, including those in the above diagnosis. They extend known meristic variation in the following characters (counts from non-type specimens given first, followed by those from Allen & Walsh in parentheses): gill rakers 7+14–16 (5+13); pseudobranchial filaments 13–16 (15); serrations on vertical portion of preopercle 21–25 (20). Differences in counts of scales above the lateral line to the fifth dorsal-fin spine and scales below the lateral line to the anal-fin origin (2–3 and 14–15 versus 1 and 10, respectively) appear to be due to different counting methods, as Allen & Walsh’s figures of the holotype clearly shows counts of 2 and at least 13, respectively. Allen & Walsh recorded the following: “caudal fin with 7+6 branched rays, 3 dorsal and 2 ventral unbranched rays, and 5 dorsal and 5 ventral procurrent rays”. With our methods, this indicates a count of 6 dorsal procurrent rays, 9+8 principal rays, and 5 ventral procurrent rays. However, examination of a radiograph of the holotype reveals 7 dorsal and 6 ventral procurrent rays, which is within variation exhibited by the three non-type specimens (6–7 dorsally and ventrally). Morphometric data for the non-type specimens are given in Table 22 .

Figures 14 B–C shows two photos of an aquarium individual from Holmes Reef displaying variation in the barring pattern on the posterior body.

We add the following new observations: scales with peripheral cteni; vertebrae 10+16 (9+17 reported by Allen & Walsh 2015, is apparently due to different counting methods); supraneurals 3; predorsal formula 0/0+0/2/1+1; dorsal pterygiophores in interneural spaces 9–13 1/1/1+1/1+1/1+1; no trisegmental pterygiophores associated with dorsal fin; terminal dorsal pterygiophore in interneural space 18; no trisegmental pterygiophore associated with anal fin; terminal anal pterygiophore in interhaemal space 5; ribs present on vertebrae 3 through 10; epineurals present on vertebrae 1 through 10; parhypural and hypurals autogenous; well-developed hypurapophysis on parhypural; epurals 3; single uroneural (posterior uroneural absent); ventral tip of cleithrum with well-developed posteroventral process; proximal tip of first anal-fin pterygiophore near distal tips of parapophyses on vertebra 10.

Shepherd et al. (2020) described P. hinano from two specimens from Tahiti, French Polynesia. They also published a photograph of a similar species from Maloelap Atoll, Republic of the Marshall Islands. They noted that P. hinano is most similar to P. bennetti , with an uncorrected pairwise genetic distance of 5.5 % for the barcode fragment of the mt COI gene, and very similar coloration and morphology. They differentiated the two species on the basis of live coloration ( P. hinano with two black spots along the dorsal fin base, and yellow dorsal- and anal-fin membranes), snout length (3.0– 3.2 in head length for P. hinano versus 4.4 in P. bennetti ), number of circumpeduncular scales (12 versus 14) and number of gill rakers (7–8+12–13 versus 5+13). None of these characters is diagnostic: P. bennetti possesses indistinct to distinct black marks on the dorsal-fin base, which are particularly prominent in preserved specimens ( Figure 14A ); comparison of fresh images of the two species suggests the apparent snout length differences are an arefact (upper jaw distended in the holotype of P. hinano ); the photos of the holotype of P. hinano suggest there are 14 not 12 circumpeduncular scales; and the number of gill rakers for P. hinano overlaps with counts given here for P. bennetti (5–7+13–16=18–23). Shepherd et al. recorded 11–12 pectoral rays for P. hinano , which is fewer than known for P. bennetti (13). However, examination of photos of the holotype of P. hinano show 13 rays. Further comparison is needed to address diagnostic morphological characters for P. bennetti and P. hinano , as well as the identity of the Marshall Island population.

Material examined. Coral Sea, Australia. AMS I.49489-001, 47.0 mm SL, Holmes Reef, outer reef slope, 125 m , T. Bennett, 3 Dec 2019 ; QM I.39334, 50.3 mm SL (holotype, radiograph only), Holmes Reef, 16°24.327′S, 147°49.442′E, 63 m , T. Bennett, 11 May 2015 ; WAM P.33842-001, 44.7 mm SL, Holmes Reef, 16°29.73′S, 147°51.83′E, 40 m , T. Bennett, Jan 2012 ; ZRC 61168, 55.1 mm SL, Holmes Reef , T. Bennett (no other data; obtained through Singapore aquarium trade).

Figures

FIGURE 7. Australian distribution records for Plectranthias sp. 1 (open circle), P. bennetti (closed circle) and P. japonicus (closed triangles).

FIGURE 14. Plectranthias bennetti, specimens from Holmes Reef, Coral Sea, Australia: A) WAM P.33842-001, 44.7 mm SL, preserved; B,C) same aquarium individual, not retained, showing variation in coloration. Photos by A.C. Gill (A) and Y.K. Tea (B,C).