Plectranthias longimanus (Weber)

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 : 77-79

Plectranthias longimanus (Weber)

Figures 3A , 5B , 31–32 ; Tables 1–16, 24

Common name: Longfin Perchlet

Pteranthias longimanus Weber 1913: 209 , fig. 54 (type locality: Paternoster Islands , Indonesia).

Plectranthias longimanus .— Allen & Russell 1986: 85 (checklist, Scott Reef).— Paxton et al. 1989: 507 (checklist).— Allen et al. 2006: 990 (checklist).— Moore et al. 2014: 182 (checklist).— Anderson 2018: 30 (checklist).— Parenti & Randall 2020: 26 (checklist). — Moore et al. 2020: appendix 1 (checklist).

Diagnosis. The following combination of characters distinguishes P. longimanus from all other congeners: dorsal rays X,12–15; fourth dorsal spine longest; pectoral rays 12–13, all rays unbranched; lateral line incomplete, with 10–17 tubed scales; greatest body depth 32.3–39.9 % SL.

Remarks. A small Plectranthias species (largest known specimen 29 mm SL; Heemstra & Randall 2009), P. longimanus is known in Australia from the Timor Sea, Great Barrier Reef, Coral Sea and southern Queensland ( Figure 32 ). Elsewhere it ranges widely throughout the Indo-west Pacific, from the east African coast to Tonga ( Heemstra & Randall 2009, Randall et al. 2003).

In their table 1 for western Indian Ocean Plectranthias, Heemstra & Randall (2009) gave a count of 15 branched caudal-fin rays for this species. In their account for the species, however, they gave a range of 13–15 branched caudal rays. All specimens examined by us had 13 (7+6) branched caudal rays.

We add the following new observations: scales with peripheral cteni; vertebrae 10+16, rarely 10+17; supraneurals 2; predorsal formula 0/0/2/1+1; dorsal pterygiophores in interneural spaces 9–13 1/1/1+1/1+1/1; no trisegmental pterygiophores associated with dorsal fin; terminal dorsal pterygiophore in interneural space 17; no trisegmental pterygiophores associated with anal fin; terminal anal pterygiophore in interhaemal space 5; ribs present on vertebrae 3 through 9–10; epineurals present on vertebrae 1 through 8–10; hypurals 1 and 2 represented by undifferentiated plate, other hypurals and parhypural autogenous ( Figure 5B ); 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.

Plectranthias longimanus is very similar to P. nanus in coloration and most morphometric and meristic features. They are apparently unique within the genus in having hypurals 1 and 2 present as an undifferentiated plate ( Figure 5B ). This potential synapomorphy has not been found in other examined Plectranthias species, where instead the two hypurals are autogenous ( Figure 5A ). The two species are distinguished from each other by the following characters: number of pectoral rays (12–13 in P. longimanus versus 14–15, rarely 13 in P. nanus ); number of tubed scales in the lateral line (12–17 versus 15–21); number of circumpeduncular scales (12 versus 12–15, usually 14); degree of development of serrations on the interopercle and subopercle (bones with 2–6 and 2–7 conspicuous serrations, respectively, versus each bone with 0–2 weak serrations; Figure 3 ); and body depth (greatest body depth 32.3–39.9 % SL and body depth at anal origin 27.1–32.0 % SL versus 29.4–33.3 % SL and 24.6–27.2 % SL, respectively). The two species also differ slightly in coloration. In particular, P. nanus is distinguished in having a pale bar on the caudal-fin base, edged posteriorly with a dark bar (or series of short bars). In contrast, P. longimanus has two dark basal spots on the caudal fin, which are edged dorsally and ventrally by pale spots (cf. Figures 31 and 39 ; see also Kawaji et al. 2019: fig. 4). As noted by Randall (1980), the two species appear to have different habitat requirements: P. longimanus appears to be found mostly around continental areas or larger islands, whereas P. nanus is restricted to smaller oceanic islands and reefs. However, the two species overlap in distribution in Australia on the Great Barrier Reef and northern Coral Sea and have been collected from the same rotenone stations (e.g. at Osprey Reef and Boot Reef, Coral Sea).

Material examined. Australia. AMS I.19445-095, 2: 22.1–22.7 mm SL, Queensland, Great Barrier Reef, channel between Yonge and Carter Reefs , 14°35′S, 145°36′E, 15 m , AMS team, 8 Nov 1975 ; AMS I.19472-121, 3: 22.6–24.2 mm SL (radiographs only), Queensland, Great Barrier Reef, north end of Yonge Reef, 14°35′S, 145°36′E, 7–15 m , AMS team, 23 Nov 1975 ; AMS I.22576-013, 2: 25.7–26.4 mm SL, Queensland, Great Barrier Reef, Escape Reef , middle of back reef edge, 15°50′S, 145°50′E, coral bommie on sand, 34 m , AMS team, 27 Oct 1981 ; AMS I.22613-016, 2: 17.0– 24.8 mm SL, AMS I.22613-052, 20.3 mm SL (subsequently cleared and stained), Queensland, Great Barrier Reef, Escape Reef North , back reef floor, 15°49′S, 145°50′E, coral and sand, 27 m , AMS team, 1 Nov 1981 ; AMS I.33711-062, 22.3 mm SL, far northern Great Barrier Reef lagoon, 1–2 nautical miles from outer reef, 10°34.48′S, 143°35.28′E, 14–15 m , AMS team, 16 Jan 1993 ; AMS I.33715-110, 24.7 mm SL, Coral Sea, Ashmore Reef , southeast corner of lagoon, 10°26.66′S, 144°26.82′E, 12–17 m , AMS team et al., 17 Jan 1993 ; NTM S.11373- 034, 25.4 mm SL, Western Australia, Scott Reef, east of Sandy Islet , 14°04′S, 121°47′E, 22–25 m, B.C. Russell, 8 Sep 1984 ; NTM S.11387-010, 14.9 mm SL, Western Australia, North Reef , east side, north of passage, 13°15′S, 121°54′E, 7–22 m, B.C. Russell, 12 Sep 1984 ; NTM S.13410-001, 18.2 mm SL, Western Australia, Cartier Reef , 12°31.4′S, 123°33.3′E, 12–23 m, J. Short, 7 May 1992 ; WAM P.28534-021, 22.8 mm SL, Great Barrier Reef, Ribbon Reefs , 14°58′S, 145°44′E, 25–40 m, G . R. Allen , 13 Nov 1985 .

Additional specimens identified for distribution information. AMS I.20937-027, 9.7 mm SL, Queensland , Haggerstone Island, 12°02′E, 143°17′E, 2–5 m , AMS team, 20 Feb 1979 ; AMS I.25107-071, 5: 13.6–17.0 mm SL, Coral Sea , Osprey Reef, west edge dropoff (13°56′S 146°34′E), 10–25 m , AMS team, 6 Nov 1984 ; AMS I.30465- 048, 2: 15.1–22.0 mm SL, Coral Sea , Holmes Reef, lee side, 16°30.5′S, 149°30.0′E, patch reef, 3–10 m , AMS Team; AMS I.33728-083, 4: 11.9–18.1 mm SL, Coral Sea , Ashmore Reef, northeast side, 10°09.52′S, 144°35.44′E, outer slope, 4–24 m , AMS team, 25 Jan 1993 ; AMS I.33747-053, 2: 10.0–16.0 mm SL, Coral Sea , Boot Reef, 09°58.70′S, 144°42.52′E, coral, sand and rubble, 23–30 m , AMS team, 27 Jan 1993 ; AMS I.33751-053, 20.0 mm SL, Coral Sea , Portlock Reef, east side of eastern reef in southern group, 09°35.19′S, 144°48.62′E, steep slope with coral, 5–31 m , AMS team, 29 Jan 1993 ; QM I.36357, 25.5 mm SL, Queensland , off Bunker Group, 23°49.5′S, 152°19.5′E, epibenthic sled, 50 m, Seabed Biodiversity Team, 23 May 2004 ; QM I.37740, 28.8 mm SL, Queensland , Stradbroke Island , off Point Lookout, Manta Ray Bommie, 27°25′S, 153°33′E, rotenone, 7–11 m, J. Johnson & M. Ekins, 14 Dec 2005 .

Figures

FIGURE 3. Lower part of left cheek in ventrolateral view showing serrations on interopercle (IOP), preopercle (POP) and subopercle (SOP) in: A) Plectranthias longimanus, WAM P.28534-021, 22.8 mm SL (note that mouth is open); B) P. nanus, WAM P.28541-039, 24.3 mm SL. Dotted line shows junction between interopercle and subopercle; arrows indicate antrorse serrations on preopercle; scale bars = 2 mm. Illustrations by A.C. Gill.

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 31. Plectranthias longimanus: A) aquarium specimen (not retained); B) NTM S.11373-034, 25.4 mm SL, preserved, east of Sandy Islet, Scott Reef, Western Australia. Photos by Y.K. Tea (A) and A.C. Gill (B).

FIGURE 32. Australian distribution records for Plectranthias longimanus (closed circles) and P. maculicauda (open circles).

FIGURE 39. Plectranthias nanus, specimens from Holmes Reef, Coral Sea, Australia: A) photo of aquarium specimen (not retained); B) WAM P.28541-039, 25.1 mm SL, preserved. Photos by Y.K. Tea (A) and A.C. Gill (B).