Photonectes achirus Regan and Trewavas, 1930

Flynn, A. J. & Klepadlo, C., 2012, Two new species of Photonectes (Teleostei: Stomiidae) from the Indo-Pacific, and a re-examination of P. achirus, Memoirs of Museum Victoria 69, pp. 259-267 : 266-267

Photonectes achirus Regan and Trewavas, 1930

Figures 4 , 5 ; Table 1

Material examined: AMS I.19739-018 (32.3 mm SL), 07°09.0'S, 148°52.0'E (western Solomon Sea), 110 m depth, 7 November 1969; AMS I.19753-037 (2: 25.3—30.9 mm SL), 05°51.0'S, 147°20.0'E ( Papua New Guinea, Vitiaz Straits ) , IKMT, 0—110 m depth, 4 November 1969 ; AMS I.24859-002 (78.0 mm SL), 33°43.0'—40.0'S, 152°03.0'—05.0'E ( Australia, off Sydney , NSW), bottom trawl, 0—1135 m depth, 16 October 1984 ; NMV A 30906-006 (46.4 mm SL), 0°34.836'—35.329'N, 176°56.432'—49.956'W, neuston net, 0—0.5 m depth, 6 March 2009 ; NMV A 30917-001 (46.7 mm SL), 0°14.213'—14.354'N, 176°45.843'—45.641'W, neuston net, 0—0.5m depth, 19 February 2009 ; SIO 11-305 (72.2 mm SL), 01°11.503'— 10.113'N, 176°45.152'—46.050'W , RMT, 600 m depth, 26 April 2009 ; SIO 11-306 (83.5 mm SL), 0°20.264'—18.657'N, 177°02.297'— 00.516'W , RMT, 600 m depth, 9 May 2009 ; SIO 70-333 (33.5 mm SL), 19°11.0'—04.8'N, 125°12.7'45.0'E, 10 ft IKMT, 0—2000 m depth, 13 September 1970 ; SIO 88-194 (21.4 mm SL), 24°40.5'N, 76.16'W ( Exuma Sound ) , IKMT, 200 m depth, 14 July 1986 ; SIO 88- 197 (23.0 mm SL), 25°28.0'N, 78°07.3'W (Tongue-of-the-Ocean) , IKMT, 200 m depth, 8 January 1987 ; USNM 300205 (36.7 mm SL), 21°10'N, 158°10'W , IKMT, 0—775 m depth, 8 November 1974 , 12:35—17:12, T. Clarke 74-11-4.

Diagnosis: Photonectes achirus differs from other species in the subgenus Photonectes in the following combination of characters: presence of blue luminous tissue in a band extending from pectoral region to pelvic fins, with short transverse streaks between OV photophores, and in patches on sides of isthmus, under lower jaw and above end of maxillary; length of gill filaments very long, extend beyond opercular opening; and barbel shorter than head length, with small bulb ending in a terminal appendage with a tiny bulb at tip.

Re-Examination: Body elongate, largest recorded specimen 87.0 mm SL. Morphometric and meristic values for four specimens collected from waters around Howland and Baker islands were in agreement with Morrow and Gibbs (1964): body depth 11.8—16.7% SL; head 15.4—18.7% SL (mean 14.8%); Sn-V 58.2—73.0% SL (mean 65.6%); V-vent 8.7— 21.1% SL (mean 14.4%); vent-C 15.6—22.8% SL (mean 20.1%). Eye 7.7—28.8% HL (mean 20.7%). Opercle slightly concave dorsally. Gill filament very long, feathery; extending slightly beyond gill cover; tips of filaments uncolored. Color of body black, fading to rusty brown in preservative.

Dorsal-fin rays 14—16; anal-fin rays 14—19; pelvic-fin rays 7; pectoral fins absent. Dorsal and anal fins not covered with black fleshy skin. Pelvic fins inserted closer to caudal fin than to snout tip; longest ray extending posteriorly to vent. Caudal fin forked; ventral lobe longer than dorsal lobe. All fin rays covered with melanophores along full length; membranes clear.

Photophores: IV 31-36 ( IP 8—11 + PV 22—28); VAV 11—13; AC 10—11; OA 30—35 ( OV 19—22; [rarely 23] + VAL 11—12 [rarely 9—10 or 13—15], last two photophores over anal-fin base); BR 6—8. IP series begins about halfway along isthmus length, approximately opposite posterior most BR; IP photophores noticeably smaller than body photophores. Anterior end of AC series raised, about one photophore diameter above last VAV, gently tapering to ventral profile. Secondary photophores very small, scattered over head and body; most densely clustered along dorsum; no secondary photophores on any fin-ray. Postorbital organ ovoid, with dark cap of melanophores along dorsal margin or with cluster of melanophores at anterior margin; length up to 30% HL.

Clusters of small white luminous spots on opercle. Blue luminous patch under OV-1 to OV-2; two patches along isthmus from symphysis to BR-1; pair of spots between eyes and small spots dorsal to occipito-vertebral articulation (“nape”); one pair anteriorly inside mouth; midventral stripe from below pectoral fins to pelvic fins, with short transverse streaks alternating with serial photophores.

Teeth caniniform, long and short; premaxillary teeth longest, needle-like. Premaxillary teeth 7—12; 6—8 maxillary teeth erect and 7—10 oblique; mandibular teeth 17—22; vomerine teeth 1 or 2 pairs; palatine teeth 1 pair; basibranchial teeth 4 pairs (anterior and posterior pairs separated by gap: 1 or 2 pairs followed by 2 or 3 pairs).

Barbel shorter than head length (70.0—80.0% HL). Stem covered with melanophores, terminating in a small bulb, slightly wider than stem width, with a long slender terminal appendage ending in a small bulb at tip.

Comment on Pigmentation: In older, faded museum specimens small to large dark semi-circular patches on snout and upper opercle ( Fig. 4 ; see Discussion). The dark patches were observed on older faded specimens of P. achirus ( AMS I.19739-018, SIO 70-333, SIO 88-194, SIO 88-197) on the snout between the nostrils and on the upper opercle (see Fig. 4 ). They are circular to slightly ovoid in shape, contain darker spots and are bordered by heavy pigment. Examination of more recently collected (unfaded) specimens of P. achirus ( SIO 11-305, SIO 11-306) did not reveal the colouration observed in older (faded) specimens. Several specimens did have clusters of secondary photophores at the upper opercular margin that are probably associated with the dark spots. However, other areas on the body with secondary photophores were not surrounded by any dark patches. One specimen of P.achirus ( USNM 300205) had noticeable clusters of white luminous tissue on the nape and along the opercular margin with no dark patches surrounding the clusters; snout tissue was damaged. The skin on the head of P. cf. gracilis ( USNM 300157) is in very good condition with both secondary photophores and a large cluster of white luminous tissue at the upper opercular margin; there is no indication of dark patches. Other faded Photonectes were examined for dark patches: P. albipennis ( AMS I.22l809-030, SIO 73-149), P. braueri ( AMS I.20305-013), P. caerulescens ( SIO 76-6), P. margarita ( SIO 69- 354), P. mirabilis ( AMS I.19739-018), P. parvimanus ( SIO 10- 177), P. paxtoni ( AMS I.19727-023, AMS I. 19702-043), P. waiiti ( USNM 300149, USNM 300201); none showed any trace. The significance of the tissue is unknown; it is not noticeable in fresh specimens nor is it reflective or photogenic. In reviews of dragonfishes ascribed to the family Melanostomiatidae by Beebe and Crane (1939) and Morrow and Gibbs (1964), neither work mentions these dark patches. Whether it occurs only on P. achirus is unknown at this time.

Distribution: Known from western Atlantic and Caribbean, north Pacific near Hawaii and Tasman Sea at depths of 75—1400 m ( Clarke, 1974; Froese and Paul, 2011; Morrow and Gibbs, 1964; Sutton and Hopkins, 1996) and now recorded from the equatorial western Pacific Ocean in the vicinity of Howland and Baker islands.

Comparative material examined

Photonectes albipennis ( AMS I.22809-030, SIO 73-149). Photonectes braueri ( AMS I.20305013).

Photonectes caerulescens ( SIO 76-6, USNM 256901). Photonectes cf. gracilis ( AMS I.20941-010, USNM 300157). Photonectes margarita ( SIO 69-354).

Photonectes mirabilis ( AMS I.19739-018) [re-identified as P. achirus ].

Photonectes parvimanus ( SIO 10-177).

Figures

Figure 4. Photonectes achirus, AMS I.19739-018, 32.3 mm, lateral view of head of showing dark marking at upper operculum (Photograph by C. Klepadlo).

Figure 5. Distribution of Photonectes waitti (black square), P. paxtoni (black circle), P. achirus (black triangle; white triangle = literature records). Symbols may represent more than one record