Photonectes paxtoni Flynn & Klepadlo 2012, new species
Creators: name: Flynn, A. J.
name: Klepadlo, C.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Stomiiformes
Stomiidae
Photonectes
Photonectes paxtoni

description: Photonectes paxtoni new species
Figures 3, 5; Table 1
Holotype: AMS I.1970 -243 (23.4 mm SL), 05°05'S, 145°56'E, off Madang, Papua New Guinea, 27 October 1969, 2 m IKMWT, 135 m depth.
Paratype: AMS I.19727-023 (22.4 mm SL), 05°05'S, 145°54'E, off Madang, Papua New Guinea, 27 October 1969, 2 m IKMWT, 130 m depth.
Diagnosis: Photonectes paxtoni differs from other members of the subgenus Photonectes in the following combination of characters: barbel short, with a very enlarged ovoid terminal bulb lacking terminal appendages; absence of blue luminous tissue; length of gill filaments on first branchial arch reduced, less than arch depth; and VAV photophores 15—16 (vs. 10—15), AC photophores 13 (vs. 9—12) and IV photophores 29 (vs. 30— 46). The bulb is remarkably large and plain (without filaments). The enlarged bulb is similar to P. ovibarba (synonym of P. braueri). However, P. paxtoni has no pectoral fins (vs. present, with 2 rays each), IV photophores 29 (vs. 32—33), AC photophores 13 (vs. 10—12), and the bulb lacks any terminal appendage (vs. bearing a small ovoid appendage). Another species with a large bulb, P. fimbria (synonym of P. parvimanus), can also be eliminated based on the following: IV photophores 43—49 (vs. P. paxtoni with 29), IP photophores insert near mandibular symphysis or no gap (vs. insert halfway along the isthmus, or with gap), thick skin over dorsal- and anal-fin rays (vs. thick skin absent), and bulb with terminal flap increasing with growth (vs. no flap or terminal appendage; growth change unknown).
Description: Body elongate, 22.4—23.4 mm SL; depth about seven times into length. HL 3.5—4.0 mm (15.6—17.1% SL); Sn-V 13.8—14.3 mm (61.1—61.6% SL); V-vent 3.4—3.6 mm (15.2—15.4% SL); vent-C 5.2—5.5 mm (23.2—23.5% SL) (see Table 1). Eye 1.0— 1.1 mm (25.0—27.5% HL). Opercle lobate, slightly concave dorsally. Gill filaments on first branchial arch reduced, length less than arch depth; tips of gill filaments unpigmented. Color of body rusty-brown in preservative, assumed black in life.
Dorsal-fin rays 16—18; anal-fin rays 18; pelvic-fin rays 7; pectoral fins absent. Dorsal and anal fins not covered with black fleshy skin; fin-rays covered with minute white luminous spots; membranes clear. Pelvic fins inserted closer to caudal fin than to snout tip (38.4—38.9% SL vs. 61.1—61.6% SL); longest ray extending to anal-fin origin. Caudal-fin rays broken; fin assumed forked.
Photophores: IV 29 (IP 8; PV 21); VAV 15—16 (last 2 to 3 over anal-fin base); AC 13; OA 34 (OV 20; VAL 14, last two photophores over anal-fin base); BR 8. IP series beginning posteriorly about halfway along isthmus length, opposite BR-8; photophores evenly spaced. Anterior end of AC series beginning on same level as last VAV. Secondary photophores scattered over head and body, in clusters along dorsum, tapering ventrally to between each OA photophore, continuing ventrally between each IV photophore, and in clusters along ventral surface; none on any fin rays. Postorbital organ ovoid, elongate, about equal to eye diameter. One PRO and one SO photophore on operculum, and one postorbital photophore. Specimen AMS I.1927 -023 with a pair of white luminous spots on snout between nostrils. Blue luminous tissue and dark markings absent.
Teeth caniniform, long and short; premaxillary teeth longest, needle-like. Premaxillary teeth 4; 5—7 maxillary teeth erect and 8 oblique; mandibular teeth 12—15; vomerine teeth one pair; palatine teeth absent; basibranchial teeth 4 (one pair anteriorly and two single teeth midlength). Vomerine teeth long, length equal to longest premaxillary tooth.
Barbel short, 1.5—1.8 mm (42.9—45.0% HL), with very large ovoid bulb. Stem short, ~1.0 mm (~25% HL), pigment tapering anteriorly onto base of bulb in a small V-shape; no secondary photophores on stem. Bulb large and simple, with no appendages or terminal filaments; width ~1.0 mm. Color of bulb in life unknown.
Distribution: Known only from type locality off Madang, Papua New Guinea; depth 130— 135 m.
Etymology: The name recognises Dr. John Paxton for his many contributions to the study of mesopelagic fishes and for his encouragement to the authors.
Remarks: Photonectes paxtoni is currently known from two specimens from shallow collections (depth 130—135 m). They were located among 46-year-old museum specimens labeled Photonectes sp.
description: Published as part of Flynn, A. J. & Klepadlo, C., 2012, Two new species of Photonectes (Teleostei: Stomiidae) from the Indo-Pacific, and a re-examination of P. achirus, pp. 259-267 in Memoirs of Museum Victoria 69 on pages 265-266, DOI: 10.24199/j.mmv.2012.69.04, http://zenodo.org/record/10666120