Pseudoscopelus cephalus Fowler 1934

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 : 24-26

Pseudoscopelus cephalus Fowler 1934

Figures 7 A , 9 C , 10 A , 28 C.

Pseudoscopelus cephalus Fowler 1934: 361 , figure 111 [type locality western Central Pacific, Philippines Islands, 9º38’ N, 121º11’ E]; de Beaufort in de Beaufort and Chapman 1951: 7–8, figure 4 [western Central Pacific]; Prokofiev and Kukuev 2005: 231 [resdescription based on photographs and x-ray of holotype]; 2006c [key to species]; 2008: 81– 87, figures 129–135 [resdescription based on photographs and x-ray of holotype].

Pseudoscopelus sagamianus (non Tanaka 1908) Lavenberg 1974: 287–302 [in part, synonymy proposed not in accordance to the ICZN 1999].

Diagnosis. A species of the Pseudoscopelus scriptus species group, which can be distinguished from its congeners by a unique characteristic: a low number of vertebrae, total vertebrae 31; precaudal vertebrae 14 (vs. 35–38, 16– 18 in all other species of Pseudoscopelus ).

Description. Middle-sized species, only specimen examined with 74.0 mm. Morphometric data not available due to severe damages in holotype (see remarks). General body shape as described for genus with diagnostic characteristics of species and species group.

First dorsal-fin rays viii (1*); second dorsal-fin rays ii+20 (1*); anal-fin rays iii+19 (1*); pectoral-fin rays 14 (1*); pelvic-fin rays I+5 (1*); caudal-fin rays i+7+8+i (1*). Branchiostegal rays 7 (1*). Pre-caudal vertebrae 14 (1*); total vertebrae 31 (1*).

Lateral line complete; broken. Temporal canal damaged; supratemporal canal 3 (1*); otic canal damaged; supraorbital canal 6 (1*); supranasal pore 2 (1*); epiphyseal branch 3 (1*); infraorbital canal 11 (1*); preopercular canal 5 (1*); mandibular canal 6 (1*); fifth pore of mandibular canal 2 (1*).

Dentition. Enlarged teeth on premaxilla, dentary and palatine. Teeth arrangement as illustrated for Pseudoscopelus scriptus . Premaxilla moderately wide, widest point on body 15–17% in premaxillary length.

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

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 in transverse rows of one to four teeth; teeth straight, needle-like, gradually increasing in size from lateral to mesial. Palatine teeth 7 (1*).

Teeth on infrapharyngobranchials and fifth ceratobranchial, conical, curved. Teeth on second basibranchial 6 (1*), conical, in V -shaped or single, irregular row. Teeth absent on basihyal and other basibranchials. Gill rakers on first epibranchial 0 (1*); first ceratobranchial 13 (1*); first hypobranchial 8 (1*). Gill rakers absent on other elements.

Luminescent organs. Luminescent organs present as discrete photophores on head and body ( Fig. 10 A ). Most of photophores partially destroyed by loss of skin or washed out, see remarks for details. Photophores on head: apf, dnf, inof 1–2, lpf, opf, pof, and vnf absent or not preserved. mxf elongated, in single row, parallel to maxilla, from level of posterior margin of eye to posterior third of maxilla; ppf poorly preserved on left side, completely destroyed on right; amf not preserved or absent; pmf partially preserved, in one to two rows, lateral to mandibular canal, from halfway between fourth and fifth pores to halfway between fifth and sixth pores.

Photophores on body: lvf, rtf, spf, and svf absent or not preserved; scf present as three photophores in posterior part of peduncle; pf in single row along ventral-most pectoral-fin ray, continuous with paf; vf in single row, along mesial pelvic-fin ray; vaf continuous with vf and trf, extending over base of pelvic rays 3-5; if and prvf continuous, in irregular two rows, from isthmus to anterior part of pelvic girdle; ptvf in two rows, from posterior half of pelvic fin to close to anus; trf laterally in single row, with medial circular group of photophores; saf in two rows, with smaller photophores closely spaced and ventral, and larger photophores widely spaced and dorsal, heart-shaped, extending anteriorly beyond anus, not preserved posteriorly; prcf in posterior half of peduncle, elongated, three-pronged, medial prong extending over anteriormost lower procurrent rays.

Color. Known from the holotype, which is entirely beached white.

Distribution. Known only from Indo-Pacific, off the Philippines; from 9º38’ N, 121º11’ E ( Fig. 7 A ).

Bathymetric distribution. Mesopelagic; holotype collected to 940 m.

Remarks. Pseudoscopelus cephalus is only known from the poorly preserved holotype, with severe damage: the head is almost disconnected from body; the opercle is destroyed on both sides; the pectoral, pelvic, second dorsal and anal fins have their tips broken; the skin is partially destroyed on the cheeks of both sides, and the area between head and first dorsal fin, opercles, and dorsal part of peduncle. Despite the damage, apparently none of the vertebrae have been lost; the groups of photophores amf, left and part of right side pmf, vnf, posterior part of mxf, ppf, left side and anterior part of saf are not preserved.

Figures

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 9. Pseudoscopelus sagamianus: (A) FMNH 55551, 143.5 mm; (B) BMNH 1984.1.1.93, 97.8 mm. Pseudoscopelus cephalus: (C) USNM 93142, 74.5 mm, holotype.

FIGURE 10. Schematic drawing of the photophore pattern in lateral and ventral views of (A) Pseudoscopelus cephalus, USNM 93142, 74.5 mm, holotype; and (B) P. obtusifrons, USNM 268429, 115.2 mm. Dashed lines indicate level of anus and damaged area in the holotype of P. cephalus (see text for details).