Pseudoscopelus sagamianus Tanaka 1908

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 : 21-24

Pseudoscopelus sagamianus Tanaka 1908

Figures 6 B , 7 A , 9 A–B , 28 B; Table 3.

Pseudoscopelus scriptus sagamianus Tanaka 1908: 13–17 , plate 1, figure 2 [original type locality: Sagami Sea, Japan; May-1907, A. Owston col.; two syntypes, whereabouts unknown.]; Parr 1933: 29 [key to subspecies].

Pseudoscopelus sagamianus Tanaka 1912: 180–183 , plate 68, figure 188 [Sagami Sea, Japan]; Matsuda et al. 1984: 221, plate 217, figure D [western North Pacific, off Japan]; Lavenberg 1974: 287–302, figures 51, 56–58 [West Pacific to Hawaii]; Nakabo 2002: 1073 [key to species]; Prokofiev and Kukuev 2006a: 221–225 [questionable identification from eastern Indian]; 2006c [key to species, questionable]; 2008: 112–120, figures 163–173 [questionable identification from eastern Indian, eastern South Atlantic; western North Atlantic]; Prokofiev 2009, figures 1–3 [redescription and designation of neotype; in part; locality of neotype: northeast Pacific, 40°0' N, 165°0' W, R/V Kaiyo-Maru, KMT, June 12, 1992, leg. A. Yatsu, neotype NSMT 35337, 138 mm].

Diagnosis. A species of the Pseudoscopelus scriptus species group, which can be distinguished within the group by a single characteristic: internal part of mouth black, including the roof of mouth and gill arches. Bleached specimens can be further distinguished from P. scriptus by saf extending anteriorly beyond and the level of anus (vs. saf not extending anteriorly to anus); from P. pierbartus and P. obtusifrons by mesial series of premaxillary teeth in three to four rows (vs. mesial series in a single row); from P. cordilluminatus by mesial series of teeth arranged in rows of three to four teeth gradually increasing in size from lateral to mesial (vs. mesial series arranged in rows of two to three teeth, with internal row much larger than other teeth); from P. cephalus by total vertebrae 35–36, precaudal 18–19 (vs. 31, 14).

Description. Middle-sized species, largest specimen examined 143.0 mm SL. Morphometric data summarized in Table 3. General body shape as described for genus with diagnostic characteristics of species and species group.

First dorsal-fin rays vii (1), viii (3*), ix (4); second dorsal-fin rays ii+19 (1), ii+20 (5*), ii+21 (3); anal-fin rays iii+18 (1), iii+19 (4*), iii+20 (3), iii+21 (1); pectoral-fin rays 13 (5*), 14 (4); pelvic-fin rays I+5 (9*); caudal-fin rays i+7+8+i (8*), i+8+8+i (1). Branchiostegal rays 7 (9*). Pre-caudal vertebrae 18 (5), 19 (1); total vertebrae 35 (1), 36 (5).

Lateral line complete; lateral-line pores 73 (1), 74 (1), 76 (3), 77 (2*). Pores in temporal canal 2 (9*); supratemporal canal 3 (9*); otic canal 2 (9*); supraorbital canal 5 (9*); supranasal pore 2 (9*); epiphyseal branch 2 (6*), 3 (2); infraorbital canal 11 (6*), 12 (2); preopercular canal 5 (9*); mandibular canal 6 (9*); fifth pore of mandibular canal (2*).

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 5 (4), 6 (2), 7 (1*), 8 (2).

Teeth on infrapharyngobranchials and fifth ceratobranchial, conical, curved. Teeth on second basibranchial 5 (1), 7 (2), 8 (1*), 9 (3), 10 (2), conical, in V -shaped or single, irregular row. Teeth absent on basihyal and other basibranchials. Gill rakers on first epibranchial 0 (9*); first ceratobranchial 11 (1), 12 (4*), 13 (1), 17 (1), 18 (1); first hypobranchial 4 (1*), 5 (1), 7 (3), 8 (2), 11 (1), 18 (1). Gill rakers absent on other elements.

Luminescent organs. Luminescent organs present as discrete photophores on head and body ( Fig. 6 B ). Photophores on head: apf, dnf, inof 1–2, lpf, opf, and pof absent; mxf elongated, in single row anteriorly, and two posteriorly, parallel to maxilla, from posterior edge of eye to angle between preopercle and dentary; vnf variable, absent from most specimens, if present as small patch posterior to anteriormost supraorbital pore; ppf as small patch in ventral edge of interopercle; amf in two to three rows, medial to mandibular canal,, medial to mandibular canal, from second pore to halfway between third and fourth pores; pmf in one to three rows, lateral to mandibular canal, from halfway between fourth and fifth pores to halfway between fifth and sixth pores.

Photophores on body: lvf, rtf, scf, spf, and svf absent; pf in single row extending to half pectoral fin, on ventral ray; paf continuous with pf, at pectoral-fin axil; 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 rows of two photophores, from isthmus to anterior part of pelvic girdle; ptvf in rows of two photophores, 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 far anterior to anus, to almost halfway between pelvic and anal fins, and connected posteriorly; prcf in posterior half of peduncle, oval or three-pronged, medial prong extending over anteriormost lower procurrent rays.

Distribution. In the Western Pacific from Japan to New Zealand; in the western Indian from off Indonesia; from 35º N to 40º S, 114º E to 132º W ( Fig. 7 A ).

Color. Two specimens collected off Japan (CAS-SU 64331 and FMNH 55551) severely bleached white, and one (CAS-SU 25626) with coloration poorly preserved in few areas; color description is based on specimens with preserved colors (BMNH 1984.1.1.83, 1984.1.1.84, and NMNZ P. 26211). Body uniformly black or dark brown, except for triangular area on epiphyseal branch. Pectoral fin mostly hyaline; pelvic, dorsal, anal, and caudal fins with few melanophores over rays and fin bases. Internal part of mouth and gill arches black, including skin on toothed area of premaxilla and dentary, over basihyal and basibranchials, roof, floor and lateral wall of mouth, internal part of opercle, membrane between dentaries and premaxillae, and gill arches; gill filaments pale.

Bathymetric distribution. Bathypelagic and probably mesopelagic; only a single lot had the depth of capture recorded, from 1060 to 1200 m.

Remarks. There are several cases of misidentification of Pseudoscopelus sagamianus in the recent literature. Pseudoscopelus sagamianus was originally described as a subspecies of P. scriptus and was either considered as a valid species (e.g., Prokofiev & Kukuev 2006 a, 2006c; Melo et al. 2007) or a subspecies of P. scriptus (e.g., Parr 1933). Of the several records made by Prokofiev and Kukuev (2006 a, 2006c, 2008, 2009), those for the North Atlantic are actually P. scriptus , and those for the eastern South Atlantic and western Indian are P. cordilluminatus . Prokofiev and Kukuev (2006a: 224; 2008: 113) erroneously described the mouth coloration of P. sagamianus as pale.

Prokofiev and Kukuev (2006 a, 2006 c, 2008) and Prokofiev (2009) were unable to separate P. sagamianus from P. scriptus and P. cordilluminatus correctly. As result they proposed erroneous diagnosis, characteristics for their key for the species, and range for P. sagamianus and P. scriptus . Prokofiev (2008: 20) attributed some major differences of dentition pattern, arrangement of photophores and pigmentation of mouth between the tree species “less significant than the differences of other species of the genus Pseudoscopelus ” and suggested that they are subspecies.

Spitz et al. (2007) did not examine any specimen of P. sagamianus and based their diagnosis on original description and illustration made by Tanaka (1908). Their diagnosis based on the distance between the anus and anal fin is considered to be uninformative.

The type specimen. Pseudoscopelus sagamianus was described by Tanaka (1908) based on two specimens collected by Allan Owston in the Sagami Sea, Japan, Western North Pacific. Together with the type specimens of 75 species described by Tanaka, the syntypes of P. sagamianus are considered to be lost ( Eschmeyer 2007).

Prokofiev (2009) designated a neotype for P. sagamianus . His choice of neotype, however, is very problematic because it was not in accordance to some articles and recommendations of the ICZN (1999). He did not follow the Article 75.3.6 of the ICZN (1999): evidence that the neotype came as nearly as practicable from the original type locality (…) as the original name-bearing type. Despite of listing specimens from nearby areas in Japan and having specimens from the type locality available in museums in the United States, Prokofiev (2009) chose a specimen from about 5.000 kilometers away from the type locality, in the eastern North Pacific. A major consequence of his choice is that, in accordance to the Article 76.3 of the ICZN (1999), the type locality of P. sagamianus has now been changed to the place of origin of the neotype, despite any previous published statement of the type locality.

Prokofiev (2009) also did not follow the recommendation 75B: before designating a neotype, an author should be satisfied that the proposed designation does not arouse serious objection from other specialists in the group in question. There are serious objections about his choice because he did not attempt to find the type material of P. sagamianus in further museums, and he confused Pseudoscopelus sagamianus with two other species, one of which is the type species of the genus, P. scriptus , and the other is been described herein as new, P. cordilluminatus .

Figures

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 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.