Plectranthias inermis Randall

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 : 65-66

Plectranthias inermis Randall

Figures 5A , 23 ; Tables 1–16, 24

Common name: Checkered Perchlet

Plectranthias inermis Randall 1980: 135 , fig. 11, tab. 9 (type locality: Caban Island, Batangas, Luzon, Philippines; paratypes from Christmas Island).— Allen & Steene 1988: 180 (checklist, Christmas Island).— Allen 2000: 87 (checklist, Christmas Island).— Hobbs et al. 2014a: 194, tab. 1 (checklist, Christmas Island).— Anderson 2018: 28 (checklist). — Parenti & Randall 2020: 26 (checklist).

Diagnosis. The following combination of characters distinguishes P. inermis from congeners: segmented dorsal rays 16–18; third dorsal spine longest, 15.6–18.8 % SL; lateral line complete, interrupted or incomplete, consisting of 12–28 tubed scales; predorsal scales extend anteriorly to middle or posterior interorbital (at point ranging from vertical through posterior edge of orbit to vertical through middle of pupil); preopercle with 3–11 weak serrations on posterior (vertical) edge and 0–2 weak serrations on ventral edge (none antrorse).

Remarks. A relatively small species (largest specimen 44.8 mm SL, Heemstra 1980), P. inermis is known in Australia only from Christmas Island. Elsewhere it is widely distributed, ranging from Mauritius in the western Indian Ocean to Fiji in the Pacific ( Randall 1980; Heemstra 1996; Heemstra & Randall 2009). Its small size and bright coloration make it desirable as an aquarium fish, and it frequently enters the aquarium trade, often under the names “Geometric Perchlet” or “Geometric Hawkfish” (a misnomer, resulting from confusion with members of the superficially similar Cirrhitidae ). Two specimens were obtained by the first author through the US aquarium trade, and subsequently cleared and stained ( Taylor & van Dyke 1985). The two specimens form the basis of our summary of osteological features of the species, as radiographs of other specimens lacked adequate detail.

Randall (1980, 1996) reported this species as having an incomplete lateral line. However, Heemstra (1996) and Heemstra & Randall (2009) later reported that the species may have an interrupted or complete lateral line. Several specimens examined in this study also have interrupted or complete lateral lines, which consist of 12–28 tubed scales.

Katayama & Masuda (1980) described P. altipinnatus from the holotype from the Izu Peninsula, Japan. They compared the species only with P. morgansi ( Smith, 1961) from east Africa. However, the species is clearly more closely related to P. inermis , having similar meristic and morphometric details, an elongate third dorsal spine bearing a pennant-like filament, and weak serrations on the preopercle. The two species differ in live coloration details (cf. Figures 23A and 24 ): P. inermis has a red and white checkered pattern on the body, with the pattern extending on to the posterior abdomen, anal-fin base and caudal peduncle; in contrast, in P. altipinnatus , the upper body is mostly red, from which extend 4–5 short red to yellow bars, with five short red bars ventrally (one on mid-abdomen, one near the anal-fin origin, one near the anal-fin termination, and two on the caudal peduncle). However, a detailed morphological comparison of the two nominal species is required. We have not attempted such a comparison in the present study.

We add the following new observations for P. inermis : scales with peripheral cteni; vertebrae 10+16; supraneurals 3; predorsal formula 0/0+0/2/1+1; dorsal pterygiophores in interneural spaces 9–13 1/1/1+1/1/1+1, 1/1/1+1/1+1/1+1 or 1/1/1+1/1+1/1+1+1; no trisegmental pterygiophores associated with dorsal fin; terminal dorsal pterygiophore in interneural space 18; no trisegmental pterygiophores associated with anal fin; terminal anal pterygiophore in interhaemal space 4–5; ribs present on vertebrae 3 through 10; epineurals present on vertebrae 1 through 11; parhypural and hypurals autogenous ( Figure 5A ); 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.

Morphometric data are summarised in Table 24.

Material examined. No data. AMS I.45300-250, 2: 28.0–30.0 mm SL (cleared and stained), no data (ex-aquarium specimens). Christmas Island, Australia . WAM P.26125-008, 25.5 mm SL (paratype), Flying Fish Cove , 10°29′S, 105°40′E, 55–65 m, G . R. Allen & R.C. Steene , 12 Apr 1978. Indonesia . AMS I.34500-045, 20.8 mm SL, Flores , west-nor-west side of Bisar, Panda Reef, 8°25.8′S, 122°19.7′E, 29–30 m , T. Trnski et al., 24 Nov 1993 . Papua New Guinea. NTM S.13687-015, 7: 19.1–32.0 mm SL, Madang, reef off Wongat Island , 5°09′S, 145°48′E, 29–32 m, H.K. Larson & M. Jebb, 22 Oct 1992 .

Figures

FIGURE 5. Caudal skeletons of A) Plectranthias inermis, AMS I.45300-250, 28.0 mm SL, showing autogenous hypurals 1 and 2; B) P. longimanus, AMS I.22613-052, 20.3 mm SL, showing undifferentiated hypurals 1 and 2. Abbreviations: EP1–3, epurals 1–3; HSP, haemal spines; HYP1–5, hypurals 1 through 5; HYPAP, hypurapophysis; NSP, neural spines; PARHYP, parhypural; PU2–3, preural centrum 2 and 3; UR, uroneural. Cartilage shown in dark grey; arrows indicate outer principal caudal rays; scale bars = 1 mm. Illustrations by A.C. Gill.

FIGURE 23. Plectranthias inermis: A) live aquarium specimen (not retained); B) WAM P.26125-008, 25.5 mm SL, paratype, preserved, Flying Fish Cove, Christmas Island, Indian Ocean, Australia. Photos by Y.K. Tea (A) and A.C. Gill (B).

FIGURE 24. Plectranthias altipinnatus, aquarium specimen from Izu Peninsula, Japan. Photo by Y.K. Tea.