Photonectes, Gunther, 1887

Prokofiev, Artem M. & Frable, Benjamin W., 2023, New specimens and supplementary descriptions of two rare dragonfishes Photonectes klepadloae and P. litvinovi, with comments on the distribution of P filipendulus (Teleostei: Stomiidae: Melanostomiinae), Zootaxa 5228 (4), pp. 489-500 : 497-498

Revised key to species of Photonectes

1a. IV 49–50; OV 38; VAL 2–4; VAV clustered in three groups; pectoral fin absent; vertebrae 67...... P. munificus Gibbs, 1968

1b. IV 28–45; OV 18–32; VAL 9–15; all VAV equally spaced; pectoral fin present or absent; vertebrae 48–63............... 2

2a. Pectoral fin present, with one to three rays (rarely perhaps completely reduced in P. filipendulus , then BR 11–12, IV 45, vertebrae 59–62)...................................................................................... 3

2b. Pectoral fin absent; BR 6–10, IV 29–39; vertebrae 48–55.................................................... 12

3a. Premaxillary and lower-jaw dentition heterogeneous in juveniles up to 70 mm SL, homogeneous in fishes of larger size; premaxillary dentition uniserial at all ontogenetic stages; first pair of IP photophores separated from the top of isthmus by a distance equal to the space between IP-1 and IP-2; all IP photophores equally spaced; vertebrae 57–63................. 4

3b. Premaxillary and lower-jaw dentition heterogeneous in both juveniles and adults; premaxillary dentition biserial; first pair of IP photophores separated from the top of isthmus by a distance much greater the space between IP-1 and IP-2; some IP photophores irregularly spaced; vertebrae 50–53............................................................ 8

4a. Bulb of mental barbel with internal black pigmentation and a compressed lamellate distal appendage (Prokofiev 2019: fig. 6d)......................................................................... P. xenopogon Prokofiev, 2019

4b. Bulb of mental barbel, when present, lacking internal pigmentation; distal appendages, when present, filiform, finger-like, or lobate ( Regan & Trewavas 1930: figs. 119–122)............................................................ 5

5a. A single short and flexible pectoral-fin ray (rarely perhaps completely reduced); mental barbel possessing a small terminal bulb with 2 to 4 short filiform distal appendages (Prokofiev 2019: figs. 4k–n)................. P. filipendulus Prokofiev, 2019

5b. Pectoral-fin rays 1 or 2 (rarely 3), when ray is single, long and stout; bulb of mental barbel, when present, with numerous or non-filiform appendages............................................................................... 6

6a. IV 40; white luminous spots present on interorbital area; pectoral fin with two flexible rays of similar length........................................................................................ P. gorodinskii Prokofiev, 2015

6b. IV 42–48; no white luminous spots in interorbital area; pectoral fin of variable structure............................. 7

7a. Pectoral fin usually with two flexible rays of similar length, rarely third vestigial ray present; bulb of mental barbel large, ovoid, with a large lobe-like to slender subterminal appendage bearing the secondary filiform filaments (those may be absent in small juveniles) (Prokofiev 2019: figs. 3l–n).................................... P. parvimanus Regan & Trewavas, 1930

7b. Pectoral fin usually with a single long and stout ray, sometimes a second ray present, always much shorter than the first one; bulb of mental barbel, when present, not inflated, bearing the numerous filiform or finger-like filaments of different sizes (Prokofiev 2019: figs. 3a–k)............................................. …. P. margarita ( Goode & Bean, 1896)

8a. Bulb of mental barbel with an elongate distal appendage; top of snout with a pair of white luminous spots [only juveniles are known]............................................................................................. 9

8b. Bulb of mental barbel lacking appendages or with a minute spherical or filiform appendage, usually completely reduced in adults; no luminous spots on top of snout................................................................. 10

9a. Bulb of mental barbel elongate, with a compressed distal appendage bifurcated at tip ( Regan & Trewavas 1930: fig. 115b); gill filaments on first arch long................................................. P. dinema Regan & Trewavas, 1930

9b. Bulb of mental barbel spherical, with a slender distal appendage terminated by a minute bulblet ( Regan & Trewavas 1930: fig. 115a); gill filaments on first arch shortened................................. P. leucospilus Regan & Trewavas, 1930

10a. Postorbital organ very long, 5.8–6.1% SL............................................ P. uncinatus Prokofiev, 2015

10b. Postorbital organ shorter, 3.3–3.6% SL................................................................... 11

11a. Bulb of mental barbel and its appendages completely reduced in adults.................... P. braueri ( Zugmayer, 1913)

11b. Bulb of mental barbel present, ending into a small filiform appendage in adults............. P. distichodon Prokofiev, 2019

12a. Dorsal branch of mental barbel present................................................................... 13

12b. Dorsal branch of mental barbel absent................................................................... 15

13a. Blue luminous tissue absent; mental barbel with large bulb; snout as long as eye (may be a size-dependent character); dentary teeth 16; anal-fin rays 16......................................................... P. corynodes Klepadlo, 2011

13b. Blue luminous tissue present; mental barbel with or without bulbs; snout shorter than eye (may be a size-dependent character); dentary teeth 23–37; anal-fin rays 18–20................................................................. 14

14a. Mental barbel with several bulbs of different size; 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; three pairs of luminous spots inside mouth and a spot above last BR photophore.................. P. mirabilis Parr, 1927

14b. Mental barbel lacking bulbs; blue luminous tissue on body consisting of three longitudinal lines in prepelvic area; no luminous spots inside mouth or above last BR photophore....................................... P. litvinovi Prokofiev, 2014

15a. Blue luminous tissue present on body and sometimes head................................................... 16

15b. Blue luminous tissue absent........................................................................... 23

16a. Anterior edge of photogenic gland of postorbital organ on vertical with suborbital organ; blue luminous tissue on body represented by two well-spaced interrupted midventral lines extending from isthmus to pelvic-fin origin and an isolated streaklike patch on each side above 10–12 th PV photophores; a pair of enlarged stalked photophore-like structures at distal extremity of barbel stem......................................................... P. klepadloae Prokofiev & Frable, 2021

16b. Anterior edge of photogenic gland of postorbital organ behind vertical of posterior border of eye; blue luminous tissue not as above; no enlarged stalked photophore-like structures on barbel stem........................................... 17

17a. IP 6; blue luminous tissue on body represented by vertical streaks between IV photophores, streaks in a line above the anteriormost IV photophores and along the posterior margin of gill opening, not forming the midventral or midlateral longitudinal lines; a longitudinal line of blue tissue along outer margin of lower jaw.......................... P. banshee Koeda & Ho, 2019

17b. IP 9–11; blue luminous tissue on body not as above, always forming midventral (at least on isthmus) or midlateral (at least in posterior half of body) longitudinal lines; no longitudinal line of blue tissue on lower jaw.......................... 18

18a. Mental barbel expanded toward tip, lacking bulbs or filiform unpigmented terminal appendage, but unpigmented and apparently luminous in distal portion ( Prokofiev & Klepadlo 2019: 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; lateral longitudinal band of blue tissue diffuse and irregular, not extending anteriad from vertical of pelvic-fin origin ............................................................................................... P. cyanogrammicus Prokofiev & Klepadlo, 2019

18b. Mental barbel with bulb(s) and/or unpigmented filiform terminal appendage, the latter two or more times narrower than the pigmented stem of barbel; blue luminous tissue not as above.................................................. 19

19a. Solid longitudinal band of blue luminous tissue present on flanks between gill opening and caudal-fin base............. 20

19b. No such band....................................................................................... 21

20a. Mental barbel lacking bulb, with thin unpigmented terminal filament splitting at tip into three short filaments; barbel not longer than eye diameter.............................................................. P. gracilis Goode & Bean, 1896

20b. Mental barbel with large spherical bulb bearing thin solidly pigmented terminal filament splitting at tip into four short filaments; barbel much longer than eye diameter................................. P. sphaerolampas Prokofiev & Klepadlo, 2019

21a. Blue luminous tissue consisting of a pair of lines along midline of isthmus, running outward of IP photophores at IP-1–IP-2 and disappearing behind PV-4 ........................................................ P. venetaenia Prokofiev, 2016

21b. 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............................... 22

22a. Mental 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 Regan & Trewavas, 1930

22b. Mental barbel without bulb; no luminous spots inside mouth, no patch of luminous tissue in front of BR-1; BR 8–10.......................................................................... P. caerulescens Regan & Trewavas, 1930

23a. Mental barbel short, not exceeding half-length of lower jaw, with a large ovoid or spherical bulb lacking appendages or with a compressed leaf-like luminous appendage; no spots of white luminous tissue above gill opening..................... 24

23b. Mental barbel usually longer than lower jaw, if shorter, bearing two bulbs situated one after the other; terminal bulb with filamentous appendage; 1–2 spots of white luminous tissue above gill opening................................... 25

24a. Mental barbel with a large ovoid terminal bulb lacking appendages; VAV 15–16........ P. paxtoni Flynn & Klepadlo, 2012

24b. Mental barbel with a large spherical terminal bulb bearing a compressed leaf-like luminous appendage with irregularly indented distal margin ( Prokofiev & Klepadlo 2019: fig. 5); VAV 11–12................. P. phyllopogon Regan & Trewavas, 1930

25a. Barbel stem completely pigmented, ending by a single bulb bearing a long filiform terminal filament, sometimes with secondary bulblets.................................................................... P. albipennis ( Döderlein, 1882)

25b. Barbel with two bulbs situated one after another, or with a single terminal bulb and an unpigmented (possibly luminous) area on stem............................................................................................ 26

26a. Barbel with a single terminal bulb and a small area on stem unpigmented dorsally and laterally, but pigmented ventrally................................................................................... P. barnetti Klepadlo, 2011

26b. Mental barbel with two bulbs situated one after the other (proximal bulb sometimes not thicker than stem, but ventral surface is not pigmented in such cases)......................................................................... 27

27a. Mental barbel not shorter than head; interspace between bulbs twice or more (usually much more) the length of the distal bulb; ceratobranchial-1 with long gill filaments.............................................. .. P. coffea Klepadlo, 2011

27b. Mental barbel shorter than head; interspace between bulbs usually not exceeding the length of the distal bulb (rarely up to 1.5 times greater); ceratobranchial-1 usually with more or less shortened gill filaments....... P. waitti Flynn & Klepadlo, 2012