Photonectes litvinovi Prokofiev, 2014

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 : 493-497

Photonectes litvinovi Prokofiev, 2014

Figs. 4–7 ; Table 1

Holotype. ZMMU 23227 (formerly IOM, uncatalogued), unsexed, 150 mm SL ( Fig. 5A ), 02°20′ N, 128°12′ E, R / V Vityaz, cruise 57, station 7276, sample 162, Isaacs-Kidd midwater trawl no. 72, 3300 m wire out, 21:25–22:25, 23 March 1975.

New material. IOM 03639 , mature male, 105 mm SL (107 mm SL at time of capture) ( Fig. 5B ), western Indian Ocean , off Farquar Island, 10°36′24″–10°36′06′ S, 50°01′48″–50°13′54″ E, R / V Akademik Kurchatov, cruise 36, station 3750, sample 50, Bongo net no. 8, 200–0 m, 400 m wire out, 00:47–01:07, 11 April 1983 .

Diagnosis. Species of Photonectes , subgenus Photonectes s. str. (Prokofiev 2019: 393), with unique combination of three solid longitudinal bands of blue luminous tissue on ventral surface of body in prepelvic area ( Figs. 5C , 6 ) and mental barbel with dorsal branch but lacking developed bulbs ( Fig. 7B ).

Description. Measurements, vertebral, and fin element counts are shown in Table 1 . Snout very short, 1.9 times smaller than eye. Dorsal and anal fins opposed, shifted backward; pelvic fins inserted closer to caudal fin than to snout. Medial fins skinned, tips of pelvic fins broken. Lower lobe of caudal fin 1.4 times longer than upper lobe. Photophores: BR 7, IP 8 + 2, PV 25, IV 35, OV 22, VAV 12 (4 over anal-fin base), VAL 10+ (10 before anal-fin origin, skin missing farther back and some hindmost photophores were apparently lost), AC 11, IC 58. Distance from IP-1 to top of isthmus as long as combined length of IP series; space between IP-8 and IP-9 exceeds space between IP-9 and IP-10 by 1.5 times. Three solid longitudinal bands of blue luminescent tissue on ventral surface of body. Thick, sharply delimited midventral band is conspicuous on isthmus originating behind base of barbel, becoming indistinct in posterior half of IP series and apparently disappearing behind IP-8. Paired ventrolateral bands originate at IP-2 as thin inconspicuous lines running outward from IP series of photophores becoming much thicker and conspicuous from shoulder-girdle region on lowermost flank, twice as close to PV than OV series of photophores, disappearing in front of pelvic-fin origin. Unpaired midventral band originates behind level of shoulder girdle (traceable from PV-5) and extends along midventral line to pelvic-fin origin ( Figs. 5C, D , 6 ). Skin at midline of breast abraded, making it unclear if midventral bands on isthmus and vent are continuous ( Fig. 6 ). No other luminous tissue on head, body or inside mouth. Postorbital organ 1.3 times longer than eye, lacking anteroventral extension of jet-black tissue encircling photogenic gland ( Fig. 7A ).

Jaw dentition heterogeneous ( Fig. 7A ); premaxillary dentition biserial, with 2+1 teeth in outer row and 6 teeth in inner row; teeth in outer row and first tooth in inner row small and pointed, remaining inner teeth long, of unequal size, with barbed tips. First two teeth in outer row opposite space between second and third teeth of inner row; third tooth opposite space between fourth and fifth inner teeth. Maxilla bears 9/10 needle-like teeth of unequal length with barbed tips followed by 14/13 smaller, inclined, comb-like teeth with pointed tips. Lower-jaw teeth 34/37, longer teeth weakly barbed. Vomer possesses pair of long barbed teeth on each side, outer teeth longer than inner one. Each palatine with two smaller, closely spaced teeth with barbed tips, hind tooth longer. Basibranchial teeth in two groups, 2+2 teeth per group, posterior pair of teeth in each group longer than anterior pair. First ceratobranchial bears six clusters of small denticles, 1–3 denticles per cluster. Gill filaments of first ceratobranchial are similarly developed along whole length of bone, not extending behind gill cover. Posterior process of anguloarticular welldeveloped ( Fig. 7A ).

Barbel 1.8 times in head, reaching interspace between IP-2 and IP-3 when adpressed, lacking bulbs, with short dorsal branch, 9 times in barbel length. Barbel terminates in small oval swelling. Tips of distal swelling and of dorsal branch each bear minute bulblet; bulblets at base of terminal swelling are poorly developed. Entire barbel and its dorsal branch darkly pigmented except small pale (probably luminous) area on stem slightly (1.25 times) closer to base of dorsal branch than to base of barbel ( Fig. 7B ).

Remarks. The new specimen shows a unique arrangement of blue luminous tissue on the body but otherwise is similar to the holotype of P. litvinovi . The latter shows no blue tissue but its skin is largely abraded ( Fig. 5A ); thus, this difference likely represents an artifact of damage during collection. For other characters, the new specimen is almost identical to the holotype of P. litvinovi . Minor differences include the presence of an additional tooth in the outer row of the premaxilla, a greater number of dentary teeth (34–37 vs. 29), a much longer barbel (1.8 vs. 3.3 times in head) with a short transparent area on its stem (absent in the holotype) and scarcely expressed bulblets at base of distal swelling. The length of barbel is a size-dependent character, as documented for other species within the genus (Prokofiev 2019), whereas the other differences are likely individual variation.

Since the blue luminous tissue was not formerly documented for that species, its identification might be problematic using the existing keys (Prokofiev 2019; Prokofiev & Frable 2021). The latest key for the species of the genus in Prokofiev & Frable (2021) can be modified in the following manner to include the correct diagnostic information for P. litvinovi .

Figures

FIGURE 4. Map of distribution of Photonectes klepadloae (squares), P. litvinovi (triangles) and P. filipendulus (circles); holotypes, solid symbols; other specimens, open symbols.

FIGURE 5. Photonectes litvinovi, habitus and pattern of blue luminous tissue: (A) holotype, ZMMU 23227; (B–D) new specimen, IOM 03639: (B) lateral view; (C) ventral view; (D) ventral view of isthmus. (1) unpaired midventral blue-tissue band on isthmus; (2) anterior ends of paired lateroventral bands on isthmus; (3) paired lateroventral and unpaired medioventral bluetissue bands on vent. Scale bars: (A–C) 10 mm (D) 5 mm.

FIGURE 6. Photonectes litvinovi, schematic of blue-tissue pattern. (?) Connection between midventral bands on isthmus and vent is uncertain due to abrasion of the skin.

FIGURE 7. Photonectes litvinovi, IOM 03639, lateral view of head (A) and mental barbel (B). (1) suborbital organ (covered by skin); (2) postorbital organ; (3) posterior process of anguloarticular; (4) luminous bulblets at distal swelling; (5) dorsal branch; (6) probably luminous area on stem. Scale bars: (A) 4 mm; (B) 2 mm.