Photonectes sphaerolampas, 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 : 273-276

Photonectes sphaerolampas new species

Figs. 2–4

Photonectes phyllopogon: Parin et al., 1976: 218 , figs. 4, 5 (misidentification).

Holotype. AMS I.20941-010 , 121.0 mm SL, 12° 40.0´S, 144° 01.0´E, 0–120 m depth, 21 February 1979 .

Paratypes. AMS I.20941-033 , 127.5 and 189.0 mm SL, same data as for holotype . IOM 3583 , 72.5 mm SL, 0° 01' S, 139° 41' W, 200 m depth, R/V Akademik Kurchatov, cruise 17, sta. 1458, Isaacs-Kidd trawl no. 21, 28 January 1974.

Diagnosis. A species of Photonectes based on the following combination of characters: mental barbel with large spherical bulb bearing darkly pigmented terminal appendage splitting at tip into short filaments; solid longitudinal band of blue luminous tissue present along flanks from gill opening to caudal-fin base; a longitudinal row of small roundish spots of blue luminous tissue above IV photophores on each side of body, connecting with row on opposite side by transverse interrupted streaks of blue luminous tissue alternating with anterior 12 PV photophores, and high number of AC photophores (14–18).

Description. Body elongate, tapering toward caudal fin ( Fig. 2 ). Snout 1.0–1.2 times shorter than eye. Morphometric values, in % of SL: head length 11.5 (10.3–15.2); snout length 1.6 (1.5–2.8); eye diameter 2.0 (1.6–2.8); least interorbital width 3.8 (3.7–4.1); barbel length 5.1 (3.6–6.8); upper jaw length 13.8 (13.2–17.4); postorbital organ length 2.8 (2.6–3.5); ditto, greatest depth 1.0 (0.9–1.2), entire black surrounding area 4.5 (4.2–5.0); predorsal, preanal and prepelvic distances 77.5 (76.0–77.9), 79.2 (77.9–79.2) and 56.2 (52.9–62.8), respectively; dorsal- and anal-fin base length 14.9 (15.1–17.9) and 16.6 (16.8–19.8), respectively; pelvic-fin length 13.1 (10.1–14.5); greatest body depth 9.3 (7.2–11.7); least depth of caudal peduncle 2.1 (1.9–2.4). Opercle slightly concave dorsally, its posteroventral corner somewhat produced, rounded; gill filaments extending beyond gill cover. Gill filaments of first arch long, of equal length along ceratobranchial-1. Color of skin fading to rusty brown after more than 40 years of storage; areas encircling nares and supraorbital pores blackish.

Dorsal-fin rays 20 (16–21); anal-fin rays 20 (18–23); pelvic-fin rays 7; pectoral fins absent. Black fleshy skin extends onto bases of dorsal and anal fins only. Pelvic fins extending to vent. Caudal fin forked, tips of lobes broken, rays 9 + 9. Vertebrae 48. Photophores: IP 10 (9); PV 23 (21–23); IV 33 (31–32); VAV 12 (12–15) [last 3 over anal-fin base]; AC 17 (14–18); IC 62 (57–62); OV 18 (18–21); VAL 15 (13–15) [last 3 over anal-fin base]; OA 33 (33–34); BR 9 (8–9). Anteriormost six IP photophores smaller than remaining ones, closely spaced, with distances between them not exceeding diameter of organ; 7 th IP photophore separated from 6 th one by 1.5 of its diameter and from 8 th one by two diameters; 8 th and 9 th IP photophores closely spaced. Distance between anterior tip of isthmus and first pair of IP photophores equals to half-length of isthmus. Secondary photophores very small, scattered over head and body, most densely clustered along dorsum, between OV and PV organs and between PV organs of neighbouring sides, absent on fin-rays. Postorbital organ moderately large, elongate, tapered posteriad, 1.4 (1.3–1.6) times eye. Antero-ventral corner of jet-black tissue encircling the photogenic gland of postorbital organ extends anteriad to a vertical through the center of eye ( Fig. 3A ).

Blue luminous tissue on body arranged as follows: a solid longitudinal band along flanks from gill opening to caudal-fin base ( Fig. 3B ); a longitudinal row of small roundish spots above IV photophores on each side of body from 1 st photophore IP to 16 th photophore PV; transverse interrupted streaks alternating with PV photophores, originating from space between last IP and 1 st PV photophores and ending in interspace between 11 th and 12 th photophores of PV ( Fig. 3C ); diffuse patch of pale blue tissue in posterior portion of each mandibular ramus. Clusters of small, luminous whitish spots behind posterior end of maxillary. No luminous tissue inside mouth.

All jaw bones with heterogeneous dentition; premaxillary teeth biserial, teeth in outer row much shorter ( Fig. 3D ). Premaxillary and dentary of holotype slightly disarticulated; exact number of teeth difficult to count. Paratypes possessing 5–8 + 2–3 caniniform teeth on premaxillaries. Maxillary with 11 (7–13) erect caniniform teeth of different sizes, following by a comb-like row of inclined needle-like teeth (13 (10–19) in number); 3 rd erect maxillary teeth longest, first and last two teeth smallest. Dentary teeth 21–29 in number, unequal in length ( Fig. 3E ). Vomer with 3 + 3 (2–3 + 2–3) unequal teeth. Each palatine bearing 3 (1–3) teeth. All inner premaxillary teeth, some (anteriormost) teeth on dentary, vomerine and palatine teeth with weakly barbed tips.

Barbel moderately short (43.6 (about 35–45) % of head length), with a large spherical bulb bearing a single heavily pigmented terminal appendage with tip branched into four short processes ( Figs. 3B, 3F , 4 ). Length of bulb equal in length to its terminal appendage and about twice as short as length of pigmented stem.

Etymology. The name (Greek “σφαίρα” for spherical and “λάµπα” for lantern) reflects the characteristic shape of the bulb of the mental barbel.

Comparisons. Photonectes sphaerolampas is similar to P. gracilis in arrangement of blue luminous tissue on body, but differs from this species in the structure of mental barbel (thick pigmented stem lacking bulbs but with thin unpigmented distal appendage terminating by three short filaments in P. gracilis ), and in barbel much longer than eye (vs. as short as eye or shorter).

Photonectes sphaerolampas resembles P. phyllopogon in structure of mental barbel (both species share large spherical bulb with darkly pigmented terminal appendage). However, in P. phyllopogon this appendage ending with a flattened unpigmented (apparently luminous) extension with irregularly indented distal margin ( Fig. 5 ). Furthermore, the new species differs from P. phyllopogon in presence of blue luminous tissue on body and anteroventral extension of jet-black tissue encircling postorbital photogenic gland (both absent in P. phyllopogon ), in the uniformly long gill filaments on first ceratobranchial (vs. reduced in upper part in P. phyllopogon ), and in the higher count of AC photophores (14–18 vs. 12).

Distribution. Equatorial Western and Central Pacific.

Figures

FIGURE 2. Photonectes sphaerolampas, new species, habitus: (A) holotype; (B) 189-mm paratype. Scale bars: 10 mm.

FIGURE 3. Photonectes sphaerolampas, new species, details, (A, C–F) 72.5-mm paratype, (B) holotype: (A) postorbital organ (anteroventral extension of jet-black tissue encircling the photogenic gland arrowed); (B) head and anterior portion of body, lateral view showing solid lateral band of blue tissue and expanded mental barbel; (C) pattern of blue tissue on ventral surface of body; (D) premaxillary dentition (teeth of outer row arrowed); (E) lower jaw dentition; (F) mental barbel. Scale bars: (A, C) 2 mm; (B) 5 mm; (D–F) 1 mm.

FIGURE 4. Mental barbel of Photonectes sphaerolampas, new species. Scale bar: 0.6 mm.

FIGURE 5. Photonectes phyllopogon, IOM ASV-2669, 02° 02´ N, 36° 32´ W, 700–0 m, mental barbel. Scale bar: 0.5 mm.