Plectranthias ferrugineus, Gill & Pogonoski & Moore & Johnson, 2021

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 : 52-59

Plectranthias ferrugineus n. sp.

Figures 17–18 ; Tables 1–17, 23

Common name: Rusty Perchlet

Holotype. CSIRO H 8289-02 , 37.6 mm SL, Australia, Western Australia, north of Dampier Archipelago , 19°26.78′S, 116°41.51′E to 19°26.97′S, 116°41.37′E, 103–106 m, benthic sled, CSIRO, RV Investigator , 27 Oct 2017 ( IN2017 _ V05 /358, site W26).

Paratypes. AMS I.48200-001, 36.6 mm SL, CSIRO H 8289-04 , 41.9 mm SL, CSIRO H 8289-05 , 3 : 25.0– 35.8 mm SL, QM I.40892, 37.6 mm SL, WAM P.34819-001, 39.5 mm SL, all collected with holotype; NMV A 29686 -023 , 6 : 26.7–44.6 mm SL, Australia, Western Australia, Imperuse L23 transect, 18°25.52′S, 120°05.92′E to 18°26.2′S, 126°06.5′E, 103–105 m, beam trawl, M.F. Gomon, RV Southern Surveyor , 19 Jun 2007 (SS0507/85); NTM S.17033-001, 3: 34.0– 38.5 mm SL, Australia, Northern Territory, Arafura Sea, south of Evans Shoal , 10°22.29′S, 129°31.57′E, 102–106 m, B. Glasby, R. V. Solander , 8 Aug 2010; WAM P.34794-004, 34.5 mm SL, Australia, Western Australia, Lynher Bank , 15°50.36′S, 121°31.34′E to 15°50.37′S, 121°31.28′E, 98–99 m, epibenthic sled, J. Fromont & J. Ritchie, RV Solander , 24 Oct 2016 ( SOL1 /WA102); WAM P.34795-003, 32.3 mm SL, Australia, Western Australia, Lynher Bank , 15°29.62′S, 121°38.17′E to 15°29.58′S, 121°38.21′E, 95–96 m, epibenthic sled, J. Fromont & J. Ritchie, RV Solander , 25 Oct 2016 ( SOL52 /WA103) .

Non-types. NMV A 29690 -002 , 5 : 22.1–33.0 mm SL, Australia, Western Australia, Mermaid L 24 transect, 17°46.10′S, 120°43.15′E to 17°45.95′S, 120°42.93′E, 97–109 m, Sherman sled , FRV Southern Surveyor , 20 Jun 2007 (SS0507/97) ; NMV A 29707 -001 , 32.5 mm SL, Western Australia, Broome L 25 transect, 16°45.15′S, 121°02.80′E to 16°44.60′S, 121°02.20′E, 100–108 m, FRV Southern Surveyor , 30 Jun 2007 (SS0507/116) .

Diagnosis. The following combination of characters distinguishes P. ferrugineus from congeners: dorsal fin with 14–16, modally 15 segmented dorsal rays; fourth dorsal spine longest; pectoral fin with 13–14 unbranched rays; lateral line complete with 27–30 tubed scales; lower part of preopercle with two enlarged antrorse spines; predorsal scales extending anteriorly to anterior part of interorbital area.

Description. Dorsal rays X,14 (X,14–16), all (all or all but first) segmented rays branched; anal rays III,7, all segmented rays branched; pectoral rays 13/13 (13–14), all rays unbranched; pelvic fin I,5, all segmented rays branched; upper procurrent caudal-fin rays 6 (5–6); lower procurrent caudal-fin rays 5 (5–6); principal caudal-fin rays 9+8; branched caudal fin rays 7+7 (7+6–7); total caudal-fin rays 28 (27–29); lateral line complete with 29/? (27–30) scales; scales above lateral line to origin of dorsal fin 3/3 (2–3); scales above lateral line to base of fifth dorsal spine 2/2 (1–2); scales below lateral line to origin of anal fin 11/11 (10–12); diagonal rows of scales on cheek 5 (5–7); predorsal scales 19 (15–22); circumpeduncular scales 16 (14–16); gill rakers 6+12 (4–7+11–14=16–20), the upper 4–6 and lower 2–6 rudiments; pseudobranchial filaments 8 (8–14); branchiostegal rays 7.

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, 1/1/1+1/1/1+1 or 1/1/1+1/1+1/1+1); no trisegmental pterygiophores associated with dorsal fin; terminal dorsal pterygiophore in interneural space 17 (18); no trisegmental pterygiophores associated with anal fin; terminal anal pterygiophore in interhaemal space 4 (4–5); ribs present on vertebrae 3 through 10; epineurals present on vertebrae 1 through 12 (11–12); 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 ( Figure 17B ).

At least some dorsal-fin spines with short fleshy tabs on their distal tips (poorly preserved in all specimens, but apparent on at least some spines of several specimens); fourth dorsal spine longest, though sometimes subequal to third or fifth spine; dorsal fin incised before first segmented-fin ray (tenth spine 45–61% length of first segmented ray); soft dorsal rounded with third to eighth segmented ray longest; second anal-fin spine longest and stoutest; anal fin rounded with second or third segmented ray longest; caudal fin weakly emarginate with short filamentous extension of upper lobe; lower 7 or 8 pectoral fin rays slightly thickened, with membranes between thickened rays incised; eighth or ninth (counting from dorsal-most) pectoral ray longest, reaching vertical through posterior edge of anal-fin base; pelvic fins short, not reaching anus, second segmented ray longest.

Morphometric data are summarised in Table 23.

Mouth large, slightly oblique, posterior margin of maxilla reaching vertical through posterior edge of eye; maxilla expanded posteriorly, with long, low, lateral ridge running parallel to dorsal margin; supramaxilla present or absent, when present small and splint-like; upper jaw with band of villiform teeth, 6–7 rows wide anteriorly, reducing to 2–3 rows posteriorly, with pair of canine teeth at front of jaw, and sometimes with 1 or more stout caniniform teeth on inner part of band at symphysis; lower jaw with band of villiform teeth, 4–5 rows wide at symphysis, reducing to single row posteriorly, with 1–3 enlarged canine teeth on mid-side of jaw; vomer with V-shaped band of 2 rows of sharp-tipped conical teeth; palatine with a band of 1–2 rows of small, sharp-tipped conical teeth; ectopterygoid and mesopterygoid edentate; tongue narrow, pointed and edentate.

Opercle with 3 flat spines (one paratype with 4 spines on one side, owing to doubling of lower spine), middle spine longest, upper spine partially concealed by scales; preopercle an open groove, with about 12–20 weak serrations or crenulations on inner margin of groove, 16–29 serrations on vertical portion of outer margin, and 2 flat, antrorse spines on horizontal portion of outer margin; interopercle with 1–8 indistinct to distinct serrations; subopercle with 3–7 indistinct to distinct serrations; posttemporal with 1–4 irregular serrations. Anterior nostril positioned at middle of snout, tubular with small flap on posterior rim, overlapping posterior nostril when depressed; posterior nostril at anterior border of orbit, with slightly raised rim but no flap.

Scales ctenoid with peripheral cteni only; lateral line broadly arched over pectoral fin following body contour to caudal-fin base; predorsal scales extending anteriorly to anterior part of interorbital area at vertical through anterior edge of pupil to anterior edge of eye (one paratype with small scales extending farther to posterior nostrils on lateral part of snout); no scales on chin, branchiostegal membranes, infraorbital bones, maxilla, mandibles or snout; no auxiliary scales on head or body; dorsal fin with intermittent row of scales along base of fin; anal fin with low scaly sheath basally, with some small scales extending on to fin membranes anteriorly; caudal fin with scaly basal sheath, with small scales extending on to basal third to half of fin membranes; pectoral fins with basal sheath and small scales extending on to fin membranes.

Colour in life (based on colour photographs of holotype and paratype in CSIRO H 8289-04 when freshly dead; Figure 17A ): head and body pale tan; head with red-ochre blotches dorsally and yellow to red-ochre blotches ventrally; anterior part of jaws red-ochre; iris red-ochre, with four dark grey spots or short streaks, two in front of pupil and two behind pupil; nape red-ochre; five red-ochre blotches on dorsal part of body above lateral line, first beneath fifth and sixth dorsal-fin spines, second beneath seventh to ninth dorsal-fin spines, third beneath second and fourth segmented dorsal-fin rays, fourth beneath seventh to ninth segmented dorsal-fin rays, fifth beneath twelfth to fourteenth segmented dorsal-fin ray; a series of five ochre-red blotches immediately beneath lateral line, first beneath fifth to seventh dorsal-fin spines, second beneath eighth dorsal-fin spine and fourth segmented dorsal-fin rays, third beneath fifth to tenth segmented dorsal-fin rays, fourth just behind dorsal-fin termination, fifth on middle part of caudal peduncle; remainder of body with indistinct yellow- to red-ochre blotches and irregular markings; spinous dorsal pinkish to yellowish hyaline with one or two small reddish brown to dark grey spots on distal half of each fin spine, and indistinct dusky grey blotch between seventh and eighth fin spines; soft dorsal and remaining fins yellowish hyaline, sometimes dusky grey distally; caudal-fin base with red-ochre central spot and ventral bar.

Colour in preservative: similar to live coloration; blotches on body remain, though less distinct.

Habitat and distribution. This species is known only from beam trawls and sled captures on the North West Shelf, off Western Australia, eastwards to the Arafura Sea, Northern Territory, at a very narrow depth range of 95 to 109 m ( Figure 18 ). Video camera footage from the type locality showed the habitat to consist of low relief silty sand/mud with dense patches of crinoids and erect, cup-shaped sponges.

Comparisons. The combination of 14–16 segmented dorsal-fin rays, fourth dorsal spine longest, pectoral fin with 13–14 unbranched rays, lateral line complete with 27–30 tubed scales, and lower part of preopercle with 2 enlarged antrorse spines separates P. ferrugineus from all other described Plectranthias species except P. ryukyuensis Wada, Susuki, Senou & Motomura, 2020 and P. sagamiensis ( Katayama, 1964) . The former species was described from four specimens (41.2–61.6 mm SL) from the Okinawa Islands, Ryukyu Islands, Japan. Our comparisons with that species are based on data provided by Wada et al., as well as our original observations on a 70.5 mm SL specimen from Okinawa, obtained through the Singapore aquarium trade (AMS I.49477-001; Figure 19 ). Our comparisons with P. sagamiensis are based on Wada et al. ’s data from available type specimens from Sagami Bay, Honshu (including the holotype), and additional non-type specimens from various localities in Japan (total 22 specimens, 35.5–57.3 mm SL). Plectranthias ferrugineus differs from P. ryukyuensis in having longer third and fourth dorsalfin spines (16.4–21.3 and 19.0–24.1% SL, respectively, versus 14.4–16.5 and 17.7–18.6 % SL), and a longer first anal spine (7.4–9.4 % SL versus 5.8–7.5 % SL). It differs from P. sagamiensis in having fewer dorsal segmented rays (14–16, with a strong mode of 15, versus 15–16, usually 16) and larger eye (orbit diameter 13.1–15.4 versus 10.7–12.7 % SL).

Wada et al. (2020) recorded P. sagamienis from Indonesia and the Philippines, based on previous records by Gloerfelt-Tarp & Kailola (1984) and Iwamoto & McCosker (2014), respectively. They did not, however, examine specimens from outside of Japan. We consider the identity of the Indonesian and Philippine specimens unresolved, that they possibly represent undescribed new species. Gill & Psomadakis (2018) reported on a specimen from off Myanmar as P. sp. 1, noting that it was very similar to both P. sagamiensis and P. ferrugineus (the latter referred to as “an undescribed species from the North-west Shelf of Australia ”). The specimen differs variously from P. ferrugineus , P. ryukuensis and P. sagamiensis in having a larger head (50.2 % SL, versus 41.8–45.7 % SL in P. ferrugineus , 44.3–45.9 % SL in P. ryukuensis and 41.8–45.2 % SL in P. sagamiensis ), a deeper body (greatest body depth 44.4 % SL versus 32.4–44.5 % SL in P. ferrugineus , 36.3–39.3% SL in P. ryukuensis and 21.5–27.8 % SL in P. sagamiensis ) and longer pelvic fins (33.3 % SL, versus 26.3–34.3 % SL in P. ferrugineus , 26.0–27.6 % SL in P. ryukuensis and 21.5–27.8 % SL in P. sagamiensis ).

Although all four species have similar colour patterns, the markings appear to be generally paler in P. ferrugineus than the other species. However, this may reflect differences in mood or stress of specimens. Plectranthias sagamiensis , for example, can rapidly change coloration, such that the posterior part of the body becomes much paler ( Figure 20 ). Wada et al. (2020) noted similar coloration changes in P. ryukyuensis .

Remarks. The specific epithet is from the Latin, meaning rust coloured, and alludes to the freshly dead coloration.

A relatively small species, largest specimen examined 44.6 mm SL. A 34.0 mm SL paratype in NTM S.17033- 001 is a gravid female.

Figures

FIGURE 17. Plectranthias ferrugineus, CSIRO H 8289-02, holotype, 37.6 mm SL, Dampier Archipelago, Western Australia: A) freshly dead (photographed after three days frozen); B) radiograph. Photo and radiograph by J.J. Pogonoski.

FIGURE 18. Distribution records for Plectranthias ferrugineus n. sp. (closed circles; arrow indicates type locality), P. kamii (open circles; Australian records only, excluding Christmas Island) and P. winniensis (triangles; Australian records only).

FIGURE 19. Plectranthias ryukyuensis, AMS I.49477-001, 70.5 mm SL, from Okinawa, Ryukyu Islands, Japan. Photographed in an aquarium. Photo by Y.K. Tea.

FIGURE 20. Plectranthias sagamiensis, same aquarium specimen from Izu Peninsula, Japan, not retained, showing variation in coloration. Photos by Y.K. Tea.