Pseudoscopelus bothrorrhinos, Melo, Marcelo R. S. & Klepadlo, Cynthia, 2007

Melo, Marcelo R. S. & Klepadlo, Cynthia, 2007, Two new species of Pseudoscopelus (Teleostei: Chiasmodontidae), with a new diagnosis for the genus, Zootaxa 1605, pp. 33-46 : 41-44

Pseudoscopelus bothrorrhinos , new species

( Figs. 7 , 8 and 9 ; Tables 2 and 3)

Holotype. LACM 31502-2 (45.9), western Central Pacific, 2°51’S, 169°55’E, 1000 m, 3-V-1967, R/V Coriolis.

Paratypes. Western Central Pacific: LACM 31495-1, 1 (40.0), 0°36’S, 169°32’E, 146 m, 26-XI-1966, R/ V Coriolis; LACM 31502-1, 1 (31.4), collected with holotype; LACM 31507-1, 1 (28.4), 0°26’S, 169°45’E, 1200 m, 13-VI-1967, R/V Coriolis; LACM 31521-1, 2 (29.8-32.8), 0°18’S, 169°57’E, 1200 m, 02-IX-1967, R/V Coriolis; LACM 31522-1, 1 (31.7), 0°35’S, 169°54’E, 1200, 02-IX-1967, R/V Coriolis; LACM 31524- 1, 1 (55.1), 1°14’S, 169°49’E, 1200 m, 02-IX-1967, R/V Coriolis; LACM 36054-1, 1 (38.3), 4°49.5’S, 129°55’E, 650 m, 27-IV-1975, R/V Alpha Helix ; LACM 36059-6, 1 (27.9), 4°49’S, 129°31’E, 550 m, 07-V- 1975, R/V Alpha Helix ; SIO 07-6 (former LACM 31494-1), 2 (36.6-39.6), 0°36’S, 169°32’E, 146 m, 23-XI- 1966, R/V Coriolis; LACM 56616-1, 1 (38.1, cs), 1°42’S, 143°02’E, 0-200 m, 6-IV-1975, R/V Vityaz. Western Indian: LACM 33346-1, 1 (48.7), 12o06’S, 44°22’E, 900 m, 20-VIII-1964, Te Vega 4.

Diagnosis. Pseudoscopelus bothrorrhinos differs from all its congeners by the presence of lpf, extending dorsally to the middle of the preopercle (vs. lpf completely absent in all other species of Pseudoscopelus ). It can be further distinguished from all other Pseudoscopelus species except P. scutatus , by the concave snout (vs. snout convex on the remaining species); svf present (vs. svf absent on the remaining species); pf, paf, vf, and vaf absent (vs. pf, paf, vf, and vaf present); prvf and ptvf continuous (vs. prvf and ptvf disconnected); and by the distal radials of the first dorsal fin developed on a plate-like structure (vs. distal radials of first dorsal fin slender, not plate-like).

Description. Meristic data summarized in Table 2, and morphometric data in Table 3. Small-sized species of Pseudoscopelus , largest specimen 55.1 mm SL. Body elongate, fusiform, not greatly compressed anteriorly, but progressively more compressed along caudal region. Greatest body depth at origin of first dorsal fin. Scales absent, except for lateral line.

Anterior profile concave in lateral view, tip of snout concave, forming anterior pit containing anterior naris and first three supraorbital pores. Mouth terminal and large, reaching edge of preopercle. Orbit circular. Nares distinctly separated, anterior naris circular, at lateral edge of anterior pit; posterior naris elongate, at anterodorsal edge of eye.

Teeth present on premaxilla, dentary, and palatine. Premaxillary and dentary dentition of P. bothrorrhinos illustrated in Fig. 8 . Premaxilla wide anteriorly; premaxillary teeth arranged in three series: lateral, middle and mesial. Lateral series at edge of premaxilla, first tooth at anterior edge, curved orally, type 1; remaining teeth at lateral edge curved caudally, type 4. Middle series in rows of two straight teeth, needle-like, type 4, size increasing from lateral to mesial. Mesial series in transverse rows of one to two teeth, needle-like, type 4, size increasing from lateral to mesial. Dentary teeth in two rows: lateral and mesial. Lateral series at edge of dentary, all curved orally, type 4; mesial row in series of one to two teeth, needle-like, type 4. Palatine teeth conical, type 1, arranged in single row.

Gill arches four; pseudobranch present. Epibranchial of first arch attached to opercle to midline; ceratobranchial, hypobranchial and basibranchial of first arch free. Epibranchials of second, third and fourth arches connected anteriorly to each other and pharyngobranchials; ceratobranchial of second arch free. Hypobranchial and basibranchial of second, third and four arches connected medially to each other. Ceratobranchial of third arch connected anteriorly to fourth arch; ceratobranchial of fourth arch connected medially to body wall on anterior half. Gill rakers short, conical, similar to type 1 tooth; present on first basibranchial, first and second gill arches and pharyngeals; absent on basihyal, other basibranchials, third and fourth gill arches; rakers of first basibranchial in two rows.

Pectoral fin short, not reaching base of first dorsal fin; pelvic-fin origin slightly posterior to pectoral-fin origin. Dorsal fins two, first dorsal-fin origin slightly posterior to pelvic-fin insertion; second dorsal-fin origin at level of anal-fin origin. Distal radials of first dorsal fin developed on a plate-like structure, as in Pseudoscopelus scutatus ; total plates 9. Sensorial system of head as in Figure 2 ; pore counts listed in Table 2. Lateral line complete, with pores opening between scales; last scale of lateral line separate, on lower lobe of caudal fin, with two pores (included in lateral-line pore count). Total vertebrae 35-36 (mode=36, n=13), precaudal 17-18 (mode 18, n=10).

Color. No freshly collected specimen known, most specimens slightly bleached brown; all fin rays hyaline, including membranes. Oral and branchial cavities hyaline. Like all other described species of Pseudoscopelus , body probably entirely black or dark brown in life.

Luminescent organs. Luminescent organs present as discrete photophores on head and body; pattern of P. bothrorrhinos illustrated in Fig. 9 . Photophores on head: apf, dnf, inof 1-2, mxf, vnf, opf, pof, and ppf absent; lpf at anterior edge of preopercle, extending dorsally to middle of preopercle; amf medial on dentary, short, with few organs, restricted to gap between second and third mandibular pores; pmf in a single row, originating immediately posterior to fourth mandibular pore, extending to midpoint between fifth and sixth pores. Photophores on body: paf, pf, rtf, spf, spt, vaf, scf, and vf absent; svf anterodorsally to insertion of pelvic-fin origin, free organs halfway between svf and pectoral fin present or absent; if in two rows; prvf in single row, extending from posterior to cleithrum, passing through pelvic fins and continuous with ptvf; ptvf in two rows, extending to close to anus; saf oval, in single row, continuous anteriorly, but not connecting posteriorly, not extending anteriorly beyond anus, and connected to anal fin by single row of photophores; prcf two-pronged, extending laterally to lower procurrent caudal-fin rays.

Distribution. Pseudoscopelus bothrorrhinos is known from the equatorial regions of the western Pacific off the Gilbert Islands, Papua New Guinea, and Indonesia, and the western Indian Ocean off the Comoros Islands, east Africa ( Fig. 10 ).

Etymology. The specific name is a combination of the Greek bothros, a noun, meaning trench or pit, and rhinos, a noun, meaning nose or snout, alluding to the concave tip of the snout.

Figures

FIGURE 2. Diagram of laterosensory system of the head of Pseudoscopelus. Lateral-line canals: ESC, epiphyseal branch of supraorbital sensory canal; IO, infraorbital canal; MD, mandibular canal; MDP- 5, 5 th mandibular-canal pore; OT, otic canal; PrO, preopercular canal; SN, supranasal pore; SO, supraorbital canal; ST, supratemporal canal; T temporal canal; TR, trunk canal. Osteological abbreviations are as follows: 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.

FIGURE 7. Pseudoscopelus bothrorrhinos, new species, LACM 31502 - 2, 45.9 mm SL, holotype.

FIGURE 8. Dentition pattern of Pseudoscopelus bothrorrhinos, based on LACM 56616 - 1, paratype: (A) premaxillary, and (B) dentary; the tooth arrangement is above, and the tooth insertion sites are below, with circles proportional to the tooth-base diameter. Scale bar equals 2 mm.

FIGURE 9. Photophore pattern of Pseudoscopelus bothrorrhinos, based on LACM 31494 - 1, paratype.

FIGURE 10. Map of distribution of Pseudoscopelus lavenbergi (triangles), and P. bothrorrhinos (circles). A symbol may represent more than one locality.