Photonectes, Prokofiev & Klepadlo, 2019

Prokofiev, Artem M. & Klepadlo, Cynthia, 2019, Two new species of Photonectes with blue luminous tissue on body, and a re-examination of P. mirabilis (Teleostei: Stomiidae), Zootaxa 4590 (2), pp. 270-282 : 280

Key for identification of the species of Photonectes with blue luminous tissue on body

1a Barbel expanded toward tip, lacking bulbs or whip-like unpigmented terminal appendage, but unpigmented and apparently luminous in distal portion ( Fig. 1G ); blue luminous tissue consisting of a longitudinal row of interrupted streaks on each side above IV photophores, and transverse interrupted streaks connecting longitudinal lines of left and right sides of body between photophores of ventral rows, alternating with photophores ( Fig. 1C ); lateral longitudinal band of blue tissue diffuse and irregular ( Fig. 1D ), not extending anteriad from vertical of pelvic-fin origin............................ P. cyanogrammicus

1b Barbel with bulb(s) and/or unpigmented whip-like terminal appendage twice or more narrower than the pigmented stem of barbel; blue luminous tissue of different arrangement........................................................... 2

2a Solid longitudinal band of blue luminous tissue present on flanks between gill opening and caudal-fin base ( Fig. 9A )...... 3

2b No such band........................................................................................ 4

3a Barbel lacking bulb, with thin unpigmented terminal filament splitting on tip into three short filaments; barbel not exceeding eye in length................................................................................. P. gracilis

3b Barbel with large spherical bulb bearing thin solidly pigmented terminal filament splitting on tip into four short filaments; barbel much longer than eye................................................................. P. sphaerolampas

4a Barbel with several bulbs of different size and a short dorsal branch ( Fig. 7 ); blue luminous tissue on body consisting of a pair of longitudinal lines between IP photophores and a longitudinal row of spots (sometimes confluent into line) on each side above PV photophores; 3 pairs of spots of luminous tissue inside mouth ( Figs. 6C, 6D ) and a spot above last BR photophore ( Fig. 6F )................................................................................... P. mirabilis

4b Barbel with a single large bulb or without bulbs; blue luminous tissue on body of different arrangement; no luminous spots inside mouth and on branchiostegal membrane (except P. achirus ).............................................. 5

5a Blue luminous tissue consisting of a pair of lines along midline of isthmus ( Fig. 9B ), running outward of IP photophores at 1 st –2 nd organs of this series and disappearing above the last IP photophores.............................. P. venetaenia

5b Blue luminous tissue consisting of a midventral chevron-shaped stripe between PV photophores with short transverse streaks alternating with photophores, and a row of spots on each side above PV photophores ( Fig. 9C )....................... 6

6a Barbel with large bulb, a pair of luminous spots inside mouth and a patch of luminous tissue in front of BR-1; BR 6–8.................................................................................................. P. achirus

6b Barbel without bulb, no luminous spots inside mouth, no patch of luminous tissue in front of BR-1; BR 8–10..................................................................................................... P. caerulescens

Figures

FIGURE 1. Photonectes cyanogrammicus, new species, holotype: (A) habitus; (B) postorbital organ (anteroventral extension of jet-black tissue encircling the photogenic gland arrowed); (C) pattern of blue tissue on ventral surface of body; (D) blue tissue on flank above origin of anal fin; (E) jaw dentition; (F) premaxillary dentition, ventral view; (G) mental barbel. Scale bars: (A) 10 mm; (B, E, G) 3 mm; (C) 5 mm; (D) 2.5 mm; (F) 1.5 mm.

FIGURE 6. Photonectes mirabilis, IOM 3581: (A) habitus; (B) postorbital organ (anteroventral extension of jet-black tissue encircling the photogenic gland arrowed); (C, D) light organs inside mouth (arrowed) (C: right side; D: left side; scar-like remnants of jet-black surrounding tissue retained when photogenic tissue torn off); (E) premaxillary dentition (teeth of outer row arrowed); (F) mental barbel and adjacent region: (1) main bulb, (2) distal appendage, (3) dorsal branch, (4) luminous spot above the uppermost photophore of BR. Scale bars: (A) 5 mm; (B, E) 2.5 mm; (C, D, F) 1.5 mm.

FIGURE 7. Mental barbel of Photonectes mirabilis, IOM 3581. Scale bar: 1.5 mm.

FIGURE 9. Pattern of distribution of the blue tissue on the body in Photonectes spp.: (A) P. gracilis, IOM 1702; (B) P. venetaenia, holotype, ZM MGU 23811; (C) P. caerulescens, IOM AK-1219. Scale bars: 5 mm.