Plectranthias nanus Randall 1980: 159 Allen & Steene 1988: 180 Paxton et al. 1989: 507 Allen & Smith-Vaniz 1994: 9 Allen 2000: 87 Allen et al. 2006: 991 Allen & Erdmann 2012: 289 Hobbs et al. 2014a: 194 Hobbs et al. 2014b: 210 Anderson 2018: 31 Parenti & Randall 2020: 28 Review of Australian species of Plectranthias Bleeker and Selenanthias Tanaka (Teleostei: Serranidae: Anthiadinae), with descriptions of four new species Gill, Anthony C. Pogonoski, John J. Moore, Glenn I. Johnson, Jeffrey W. Zootaxa 2021 2021-01-26 4918 1 1 116  Anderson 2018: 31  782HJ Randall Randall [151,501,859,886] Actinopterygii Serranidae Plectranthias Animalia Perciformes 94 95 Chordata species nanus   Figures 3B, 11, 39; Tables 1–16, 24  Common name: Dwarf Perchlet      Plectranthias nanus Randall 1980: 159, fig. 22, tabs 13–14 (type locality: Cocos Island, Guam, Mariana Islands; paratypesfrom Cocos-Keeling and Christmas Islands).—  Allen & Steene 1988: 180, fig. 134 (checklist, photo, Christmas Island).—  Paxton et al.1989: 507(checklist).—  Allen & Smith-Vaniz 1994: 9(checklist, Cocos (Keeling) Islands);  Allen 2000: 87(checklist, Christmas Island);  Allen et al.2006: 991(checklist).—  Allen & Erdmann 2012: 289(diagnosis, photo, Christmas Island).—  Hobbs et al.2014a: 194, tab. 1 (checklist, Cocos (Keeling) Islandsand Christmas Island).—  Hobbs et al.2014b: 210, tab. 1 (checklist, Cocos (Keeling) Islandsand Christmas Island).—  Anderson 2018: 31(checklist). —  Parenti & Randall 2020: 28(checklist).   Diagnosis.The following combination of characters distinguishes  P. nanusfrom all other congeners: dorsal rays X,13–16; fourth dorsal spine longest; pectoral rays 13–15, rarely 13, all rays unbranched; lateral line incomplete, with 15–21 tubed scales; greatest body depth 29.4–33.3 % SL.   Remarks.A relatively small species (maximum size 39.8 mmSL, Randall 1980),  P. nanusis known in Australiafrom the Cocos (Keeling) Islands, Christmas Island, Great Barrier Reef and Coral Sea ( Figure 11). Elsewhere, it ranges widely throughout the Indo-West Pacific, as far west as the Red Sea and as far east as the Pitcairn Islandsand Hawaii ( Randall 1980; Heemstra 1996; Heemstra & Randall 2009). It closely resembles  P. longimanusin coloration, and shares with it apomorphic modification of the caudal skeleton (hypurals 1 and 2 undifferentiated, versus autogenous in other studied  Plectranthiasspecies; Figure 5). Characters distinguishing the two species are discussed under Remarks for  P. longimanus. In their table 1 and key 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. The latter count range agrees with the original description: “13 to 15, usually 13” ( Randall 1980: 162). 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; supraneurals 2; predorsal formula 0/0/2/1+1; dorsal pterygiophores in interneural spaces 9–13 1/1/1+1/1/1+1 or 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 dorsal pterygiophore in interneural space 5–6; ribs present on vertebrae 3 through 10; epineurals present on vertebrae 1 through 10–12; hypurals 1 and 2 represented by undifferentiated plate, other hypurals and parhypural 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 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). Morphometric data are summarised in Table 24.   Material examined.   Australia. AMSI.19454-088, 2: 23–24 mmSL (radiographs only), Queensland, Great Barrier Reef, channel between Yongeand Carter Reefs, 14°35′S, 145°36′E,  1–18 m,  AMSteam,  11 Nov 1975;  AMSI.20430-005, 3: 15.6–22.1 mmSL, Christmas Island, Flying Fish Cove,  5–10 m, G.  R. Allen&  R.C. Steene,  12 Jun 1978;  AMSI.20442-005, 25.8 mmSL, Christmas Island, Rocky Point,  10–12 m, G.  R. Allen&  R. Steene,  29 May 1978;  AMSI.25112-116, 3: 20.4–29.0 mm SL (subsequently cleared and stained), Coral Sea, west edge of Osprey Reef, 0.75 kmnorth of pass, 13°54′S, 146°33′E,  1–15 m, rotenone,  AMSparty,  8 Nov 1984;  WAMP.28541-039, 7: 16.4–25.1 mmSL, Coral Sea, Holmes Reef, 16°31′S, 147°50′E,  12–14 m, G.  R. Allen,  20 Nov 1985;  WAMP.29637- 027, 23.9 mmSL, Coral Sea, Lihou Reefand Cays, Georgina Cay, 17°37′S, 151°26′E,  18–29 m, G.  R. Allen et al.,  12 Nov 1987.   French Polynesia. AMSI.21646-036, 3: 23.0– 27.5 mmSL (radiographs only), Society Islands, Moorea, near Irioa Island, 17°S, 149°W,  15–20 m, B. Goldman,  18 Jun 1976.  Additional specimens identified for distribution information.   Australia. AMSI.22616-035, 26.0 mm SL, Great Barrier Reef, Escape Reef North, 15°49′S, 145°50′E, coral and sand,  5–18 m,  AMSteam,  2 Nov 1981;  AMSI.22634-006, 31.0 mm SL, Great Barrier Reef, Escape Reef North, 15°49′S, 145°50′E, reef dropoff,  18 m, W.A. Starck,  4 Dec 1981;  AMSI.25107-032, 2: 18.0– 23.5 mmSL, Coral Sea, Osprey Reef, west edge dropoff ( 13°56′S, 146°34′E),  10–25 m,  AMSteam,  6 Nov 1984;  AMSI.28993-016, 5: 17.3–27.5 mmSL, Cocos (Keeling) Islands, west side near Wreck Point, 11°19′S, 96°49′E, G.  R. Allen, 23 Fed1989;  AMSI.33747-023, 22.5 mmSL, Coral Sea, Boot Reef, 09°58.70′S, 144°42.52′E, coral, sand and rubble,  23–30 m,  AMSteam,  27 Jan 1993. 3026471477 AMS Australia Great Barrier Reef 10 -14.583333 Carter Reefs 1287 145.6 Yonge 95 96 1 Queensland 3026471349 [1086,1366,1592,1619] 1975-11-11 AMS Australia 95 96 1 3026471417 AMS Australia 8 Flying Fish Cove Christmas Island 95 96 1 3026471357 [1086,1179,1628,1654] R Allen Australia 95 96 1 3026471467 1978-06-12 R Australia Steene 95 96 1 3026471469 [221,1092,1664,1691] AMS Australia 11 Rocky Point Christmas Island 95 96 1 3026471506 [1096,1190,1664,1690] R Allen Australia 95 96 1 3026471458 1978-05-29 R Australia Steene 95 96 1 3026471399 AMS Australia 8 -13.9 Osprey Reef 1289 146.55 Coral Sea 95 96 1 3026471529 [903,1174,1736,1763] 1984-11-08 AMS Australia 95 96 1 3026471485 WAM Australia 13 -16.516666 Holmes Reef 1282 147.83333 Coral Sea 95 96 1 3026471340 [1001,1253,1772,1799] 1985-11-20 R Australia Allen 95 96 1 3026471325 WAM Australia Coral Sea 24 -17.616667 Cays 1278 151.43333 Lihou Reef 95 96 1 3026471439 1987-11-12 R Australia Allen 95 96 1 3026471329 1976-06-18 AMS B. Goldman French Polynesia Society Islands 18 -17.0 Irioa Island 40174 -149.0 Moorea 95 96 1 3026471370 AMS Australia 12 -15.816667 Great Barrier Reef 1284 145.83333 Escape Reef North 95 96 1 3026471444 [1094,1365,1952,1979] 1981-11-02 AMS Australia 95 96 1 3026471430 1981-12-04 AMS W. A. Starck Australia 18 96 97 -15.816667 Great Barrier Reef 1284 145.83333 Escape Reef North 95 96 1 3026471432 AMS Australia 18 -13.933333 Coral Sea 1289 146.56667 Osprey Reef 96 97 1 3026471538 [394,671,187,213] 1984-11-06 AMS Australia 96 97 1 3026471438 AMS Australia -11.316667 Cocos (Keeling) Islands 1295 96.816666 Wreck Point 96 97 1 3026471328 [697,943,223,249] R Fed Australia Allen 96 97 1 3026471426 AMS Australia 27 -9.978333 Coral Sea 13 144.70866 Boot Reef 96 97 1 3026471335 [943,1218,259,285] 1993-01-27 AMS Australia 96 97 1