Pseudoscopelus scutatus Krefft 1971

Melo, Marcelo R. S., 2019, A revision of the genus Pseudoscopelus Lütken (Chiasmodontidae: Acanthomorphata) with descriptions of three new species 2710, Zootaxa 2710 (1), pp. 1-78 : 45-46

Pseudoscopelus scutatus Krefft 1971

Figures 16 C , 18 B , 20 A–B , 21 A , 28 I; Table 7.

Pseudoscopelus scutatus Krefft 1971: 165–174 , Figs. 1–8 [type locality: eastern North Atlantic, 2°44’ N, 25°12’ W, holotype ISH 567a/66, 84.7 mm]; Lavenberg 1974: 183–196, figures 41–42 [Atlantic and Pacific Oceans]; Nakabo et al. 1992 [western North Pacific]; Nakabo 2002 [key to species]; Moore et al. 2003: 227 [western North Atlantic]; Figueiredo et al. 2003: 94 [literature compilation]; Prokofiev and Kukuev 2006a: 228–229, figure 5 [western North Atlantic, eastern Central Atlantic]; 2006c [key to species]; 2008: 125–136, figures 20, 50, 54–56, 69, 180–183 [in part, species account].

Diagnosis. A species of the Pseudoscopelus scutatus species group, which can be distinguished from P. bothrorrhinos by a single characteristic: lpf absent (vs. lpf present).

Description. Medium-sized species of Pseudoscopelus , largest specimen examined 91.0 mm SL. Morphometric data summarized in Table 7. General body shape as described for genus with diagnostic characteristics of species and species group.

First dorsal-fin rays vi (3), vii (8), viii (1); second dorsal-fin rays ii+20 (3), ii+21 (6), ii+22 (3); anal-fin rays ii+22 (1), iii+20 (4), iii+21 (5), iii+22 (2); pectoral-fin rays 13 (3), 14 (8), 15 (1); pelvic-fin rays I+5 (12); caudal-fin rays i+7+8+i (12). Branchiostegal rays 7 (12). Pre-caudal vertebrae 17 (5), 18 (9); total vertebrae 35 (2), 36 (10), 37 (2).

Lateral line complete; lateral-line pores 74 (1), 75 (2), 76 (2), 77 (2), 78 (2), 79 (1), 80 (1). Pores in temporal canal 2 (12); supratemporal canal 3 (12); otic canal 2 (12); supraorbital canal 6 (12); supranasal pore 3 (12); epiphyseal branch 3 (12); infraorbital canal 12 (12); preopercular canal 5 (12); mandibular canal 6 (12); fifth pore of mandibular canal 1 (12).

Dentition. Enlarged teeth on premaxilla, dentary and palatine. Premaxilla and dentary illustrated in Figure 16 C . Premaxilla narrow, widest point of premaxillary body 12–14 % in premaxillary length.

Premaxillary teeth on head, neck, body and caudal process. Lateral series of teeth in single longitudinal row, along lateral edge of premaxillary head, neck, body and caudal process; teeth slightly curved. Canine and fang on ventral shelf of premaxillary head. Middle and mesial series on ventral shelf of premaxillary body. Middle series in two, irregular, longitudinal row; teeth needle-like, straight, gradually increasing in size from lateral to medial. Mesial series in single, longitudinal row; teeth needle-like, slightly curved.

Dentary teeth in lateral and mesial series. Lateral series along lateral shelf of dentary, in single, longitudinal row, extending from symphysis to posterior tip; teeth conical, slightly curved. Mesial series on dorsal shelf of dentary, in single row; teeth straight, needle-like. Palatine teeth 3 (4), 4 (5), 5 (3); in single, longitudinal row.

Teeth on infrapharyngobranchials and fifth ceratobranchial, conical, curved. Teeth on second basibranchial 6 (2), 7 (2), 8 (2), 9 (3), 11 (1), 12 (1), conical, in V-shaped or single, irregular row. Teeth absent on basihyal and other basibranchials. Gill rakers on first epibranchial 0 (12); first ceratobranchial 5 (2), 6 (4), 7 (4), 8 (2); first hypobranchial 1 (4), 2 (5), 3 (3). Gill rakers absent on other elements.

Luminescent organs. Luminescent organs present as discrete photophores on head and body ( Fig. 21 A ). Photophores on head: dnf, inof 1–2, lpf, mxf, opf, pof and ppf absent; apf in angle between dentary and preopercle; vnf absent from most specimens, and if present as small patch posterior to anteriormost pore of supraorbital canal; amf in two to three rows, medial to mandibular canal, between second and third pores; pmf in one to two rows, anteriorly medial to mandibular canal, posteriorly lateral to mandibular canal, from forth pore to halfway between fifth and sixth pores.

Photophores on body: lvf, pf, paf, vaf, vf, trf, rtf, and spf absent; scf usually absent, present as three photophores in a single specimen (USNM 240671); if in two rows, from isthmus to ventral edge of cleithrum; prvf in irregular single row, from posterior to cleithrum, connected to ptvf posteriorly and extending to slightly anterior to anus; svf triangular, anterodorsal to pelvic-fin; saf in two rows, oval, not extending anteriorly to anus, and connected posteriorly; prcf oval-shaped or three-pronged, medial prong extending over anteriormost lower procurrent rays.

Identification of juveniles. The smallest specimen recognized has 28.4 mm (SIO 68-537); the identification was concave shape of snout and the complete development of photophore groups.

Color. Specimens preserved for long time faded to light brown. Body brown or dark brown, except for triangular area on epiphyseal branch. Pectoral, pelvic first and second dorsal, anal and caudal fins hyaline. Internal area of mouth and gill arches pale.

Distribution. Widely distributed in the Atlantic Ocean, from 40° N to 30° S, 22° to 83° W. A single record in the Indian Ocean, from the Arabian Sea; from 2°00’ N, 55°00’ W. In the Pacific Plate; from 22° N to 25° S, 100° W to 157° W ( Fig. 18 B ).

Bathymetric distribution. Meso- to bathypelagic, from 85 to 1716 m (mean 578 m).

Figures

FIGURE 1. Schematic drawing showing all the photophore groups present in the genus Pseudoscopelus. Photophores on head: anteromaxillary photophores (amf); anteropreopercular photophores (apf); dorsonasal photophores (dnf); interorbital photophores (inof 1, 2); longitudinal preopercular photophores (lpf); maxillary photophores (mxf); opercular photophores (opf); posteromandibular photophores (pmf); postorbital photophores (pof); posteropreopercular photophores (ppf); ventro-nasal photophores (vnf). Photophores on body: isthmus photophores (if); lateral pelvic-fin photophores (lvf); pectoral-fin axillary photophores (paf); pectoral-fin photophores (pf); precaudal-fin photophores (prcf); prepelvicfin photophores (prvf); postpelvic-fin photophores (ptvf); random trunk photophores (rtf); anal-fin photophores (saf); supracaudal-fin photophores (scf); suprapectoral-fin photophores (spf); suprapelvic-fin photophores (svf); transverse pelvic-fin photophores (trf); pelvic-fin axillary photophores (vaf); pelvic-fin photophores (vf).

FIGURE 2. Schematic drawing of bones and lateral-line system of head. Osteological abbreviations: den, dentary; ext, extrascapular; fr, frontal; io 1-6, infraorbitals 1–6; mx, maxilla; mst, mesethmoid; lls, lateral-line scale; na, nasal; pa, parietal; pmx, premaxilla; pop, preopercle; pto, pterotic; ptt, posttemporal; so, supraoccipital. Lateral-line system abbreviations: ESC, epiphyseal branch of supraorbital sensory canal; IO, infraorbital canal; MD, mandibular canal; MD-5, 5th mandibular-canal pore; OT, otic canal; PrO, preopercular canal; SN, supranasal pore; SO, supraorbital canal; ST, supratemporal canal; T temporal canal; and TR, trunk canal.

FIGURE 3. Schematic drawing of premaxilla (A) and dentary (B): left side with teeth illustrated and right side with site for tooth attachment represented by circles with diameter proportional to the tooth base width. The teeth filled with red represent the lateral series; with blue, middle series; with yellow, mesial series; with green, fang; and with white, canine; dashed lines represent the limits of premaxillary regions; C stands for canine, and F, for fang.

FIGURE 4. Pseudoscopelus scriptus: (A) ZMUC P. 65171, 70.0 mm, holotype; (B) USNM 240671, 104.4 mm; (C) MCZ 68449, 55.0 mm. Type series of P. stellatus (D) USNM 170941, 18.7 mm, holotype; (E) CAS-SU 66496, 6.5 mm, paratype; (F) CAS-SU 66494, 10.7 mm, paratype; (G) CAS-SU 66497, 16.7–20.3 mm, paratypes; (H) USNM 170941, holotype in ventral view; (I) USNM 170941, holotype, detail of head in lateral view; (J) USNM 170941, holotype, detail of mxf photophores in head of holotype.

FIGURE 5. Schematic drawing of dentition pattern in the species of Pseudoscopelus: (A) P. scriptus, ZMUC P 65171. 70.0 mm, holotype; (B) P. obtusifrons, LACM 20074, 100.7 mm; (C) P. pierbartus, LACM 56615, 133.4 mm; and (D) P. cordilluminatus, SIO 77-171, 97.3 mm, paratype. Premaxilla (above) and dentary (below); bones with complete dentition are represented on top, and bones with only the sites for teeth attachment on bottom; circes are proportional to diameter of tooth-base; scale bar equals 10.0 mm; C stands for canine and F, for fang.

FIGURE 6. Schematic drawing of the photophore pattern in lateral and ventral views of (A) Pseudoscopelus scriptus, ZMUC P. 65171, 70.0 mm, holotype; and (B) P. sagamianus, BMNH 1984.1.1.93, 97.8 mm. Dashed line indicates level of anus.

FIGURE 7. Maps of distribution of (A) Pseudoscopelus scriptus (diamond), P. sagamianus (star), P. cephalus (asterisk), and P. cordilluminatus (circle); (B) P. obtusifrons (cross), and P. pierbartus (triangle). Each symbol may represent more than one locality; solid symbols represent type localities.

FIGURE 8. Graphic of the species of Pseudoscopelus which allometric pectoral-fin growth is allometric in relation to the standard length is statistically significant: (A) positive growth (P=0.001) in P. scriptus (blue squares); (B) negative growth (P=0.042) in P. obtusifrons (black triangles); (C) negative growth (P<0.001) in P. australis (red dots)

FIGURE 16. Schematic drawing of dentition pattern in the species of Pseudoscopelus: (A) P. altipinnis, ZMUC P. 6546, 111.8 mm; (B) P.paxtoni, NMNZ P. 38679, 234.2 mm, paratype; (C) P. scutatus, ISH 647a-1966, 83.4 mm, paratype; (D) P. odontoglossum, SIO 61-48, 70.2 mm, holotype. Premaxilla (above) and dentary (below); bones with complete dentition are represented on top, and bones with only the sites for teeth attachment on bottom; circes are proportional to diameter of tooth-base; scale bar equals 10.0 mm; C stands for canine and F, for fang.

FIGURE 18. Maps of distribution of (A) Pseudoscopelus altipinnis (triangle) and P.paxtoni (star); (B) P. scutatus (star) and P. bothrorrhinos (diamond). Each symbol may represent more than one locality; solid symbols represent type localities.

FIGURE 20. Pseudoscopelus scutatus: (A) USNM 236776, 70.0 mm; (B) lateral view of head of ISH 567b-c/1966, 80.4 mm, paratype. Pseudoscopelus bothrorrhinos: (C) LACM 31502-2, 45.9 mm, holotype; (D) LACM 56616-1, 38.1 mm, paratype, dorsal view of a cleared stained specimen, arrows indicate the plate-like distal radials of first dorsal fin. Scale bar equals 5.0 mm.

FIGURE 21. Schematic drawing of the photophore pattern in lateral and ventral vies of (A) Pseudoscopelus scutatus, ISH 567b-c/1966, 80.4 mm, paratype; (B) P. bothrorrhinos, SIO 07-6, 39.6 mm, paratype.