Pseudoscopelus australis Prokofiev & Kukuev 2006

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 : 58-61

Pseudoscopelus australis Prokofiev & Kukuev 2006

Figures 8 C , 23 B , 24 B , 25 B , 29 L; Table 9.

Pseudoscopelus australis Prokofiev and Kukuev 2006c : S32–S36, figures 6A–G [type locality: not precisely known, Subantarctic part of the Atlantic Ocean, holotype ZM MGU (former IORAN) 21251, 150 mm]; 2006d: 71 [second species description]; 2008: 63–68, figures 13, 27–29, 32, 39, 64, 65, 70, 74, 83, 102, 112–117 [species account].

Pseudoscopelus meridionalis Lavenberg 1974: 223–233 , figures 46–47 [South Pacific; name not available in accordance to the ICZN 1999].

Pseudoscopelus altipinnis (non Parr 1933) Prokofiev and Kukuev 2005: 752, figure 2 [questionable].

Pseudoscopelus sp. A Prokofiev and Kukuev 2005: 727–729 , figure 7 [Antarctic Ocean].

Pseudoscopelus albeolus Prokofiev and Kukuev 2008: 69–76 , figures 118–124 [type locality: not precisely known, Antarctic, holotype ZIN 43959, 115.0 mm]. NEW SYNONYM.

Diagnosis. A species of the Pseudoscopelus astronesthidens species group, which can be distinguished within the group by three unique characteristics: rakers on first ceratobranchial usually absent, one small raker on proximal portion rarely present (vs. rakers on first ceratobranchial present, 2–16); ppf absent (vs. ppf present); prcf oval with three small prongs (vs. prcf U -shaped). It further differs from P. odontoglossum by having teeth on the basihyal and second basibranchial in two rows, 15–25; (vs. teeth on basihyal and second basibranchial in three rows, 28–40).

Description. Large-sized species of Pseudoscopelus , largest specimen examined 196.4 mm SL. Morphometric data summarized in Table 9. General body shape as described for genus with diagnostic characteristics of species and species group.

First dorsal-fin rays vii (2), viii (8); second dorsal-fin rays ii+20 (1), ii+21 (3), ii+22 (4), ii+23 (4); analfin rays iii+20 (1), iii+21 (6), iii+22 (5); pectoral-fin rays 11 (1), 12 (6), 13 (5); pelvic-fin rays I+5 (12); caudal-fin rays i+7+8+i (10), i+8+7+i (2). Branchiostegal rays 7 (12). Pre-caudal vertebrae 18 (8), 19 (1); total vertebrae 36 (9).

Lateral line complete; lateral-line pores 74 (1), 75 (4), 76 (3), 77 (2), 78 (1), 80 (1). Pores in temporal canal 2 (12); supratemporal canal 3 (12); otic canal 2 (12); supraorbital canal 6 (9); supranasal pore 4 (12); epiphyseal branch 3 (11), 5 (1); infraorbital canal 11 (1), 12 (11); preopercular canal 5 (12); mandibular canal 6 (12); fifth pore of mandibular canal 1 (2), 2 (9).

Dentition. Enlarged teeth on premaxilla, dentary and palatine. Teeth arrangement as illustrated for Pseudoscopelus odontoglossum . Premaxilla moderately wide, widest point of premaxillary body 15–20 % 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; posterior ten to 12 teeth on caudal process considerable thicker than anterior, type 1. Canine and fang on ventral shelf of premaxillary head. Middle and mesial series on ventral shelf of premaxillary body; middle series reaching premaxillary neck. Middle series in three, irregular transverse rows; teeth needle-like, straight, gradually increasing in size from lateral to medial. Mesial series in transverse rows, each row with one 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 on dorsal shelf of dentary, in transverse rows of one to four teeth; teeth straight, needle-like, increasing in size from lateral to mesial. Palatine teeth 10 (1), 11 (3), 12 (4), 13 (1), 14 (1), 15 (1), 16 (1); in single row, teeth needle-like, type 4; posterior three to four teeth in single row, teeth conical, type 1, similar in shape to teeth on caudal process.

Teeth on infrapharyngobranchials and fifth ceratobranchial, conical, curved. Teeth on basihyal and second basibranchial 15 (2), 16 (1), 17 (1), 18 (1), 19 (1), 20 (1), 21 (2), 22 (1), 24 (1), 25 (1), type 4, needle-like, in two rows. Teeth absent on other basibranchials. Gill rakers on first epibranchial 0 (12); first ceratobranchial 0 (9), 1 (3); first hypobranchial 0 (1), 2 (1), 4 (3), 5 (1), 6 (5), 9 (1), 12 (1). Gill rakers absent on other elements.

Luminescent organs. Luminescent organs present as discrete photophores on head and body ( Fig. 25 B ). Photophores on head: lpf, opf, pof, and ppf absent; dnf with few photophores, posterior to posterior nostril; inof one to two photophores present in one specimen ( CAS 91022), mxf short, in single row, parallel to maxilla, from level of mid-eye to posterior third of maxilla, not connected to apf posteriorly; apf in angle between preopercle and maxilla; vnf in small group of few photophores; amf in one to two rows, medial to mandibular canal, from second to fourth pore; pmf 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, scf, spf, svf and trf absent; pf in single row, in ventral ray along pectoral fin; paf continuous with pf, at pectoral-fin axil; vf in single row, along mesial pelvic-fin ray to first third of pelvic fin; vaf continuous with vf; if short, in two rows, from isthmus to cleithrum; prvf short, in two rows, from cleithrum to anterior part of pelvic bone; ptvf in two rows, from posterior third of pelvic fin to close to anus; saf in single row, not connected anteriorly at anterior angle, neither posteriorly; prcf in posterior half of peduncle, oval, three-pronged, with medial prong enlarged and extending over lower procurrent rays.

Color. Specimens preserved for long time faded to light brown or bleached white. Body uniformly black or dark brown, except for triangular area on epiphyseal branch. Pectoral, pelvic, first and second dorsal fins, anal and caudal fins dusky. Internal part of mouth pigmented including area of teeth insertion of dentary and premaxilla, roof, lateral sides and floor of mouth, skin over basihyal, basibranchials, and gill arches; gill filaments pale.

Ontogenetic changes. Pseudoscopelus australis has a negative, statistically significant allometric growth of the pectoral fin (P<0.001). The variation is illustrated in Figure 8 C , and explains the large standard length variation found for this characteristic (SD=5.6).

Distribution. Circumglobal in the cold waters of the southern hemisphere; in the Southern Ocean, eastern and western South Pacific, southern part of Indian, and eastern and western South Atlantic; from 31° S to 60° S ( Fig. 23 B ).

Bathymetric distribution. Meso- to bathypelagic; most records from 410 to 1196 m (mean 796 m); only two lots collected deeper than 1200 m ( LACM 10666-6 , 4667 m; and LACM 10862-3 , 2776 m) .

The status of Pseudoscopelus albeolus . It was first introduced by Prokofiev and Kukuev (2005), as Pseudoscopelus sp. A , and finally described by Prokofiev and Kukuev (2008) as P. albeolus . The description was based on a single specimen in extremely poor condition (see Prokofiev and Kukuev 2008, figures 118– 122), collected in 1972. The type locality is an unknown site in Antarctica. The species was diagnosed mainly because of the uniformly whitish body, but the authors also mentioned minor differences in the mdf, premaxillary teeth of the lateral series, and a few morphometric data.

Considering the poor state of the holotype and that it was collected almost years 40 prior to the description, its coloration should not be considered as representing the original pigmentation pattern. Several specimens of Pseudoscopelus used for this revision are severely faded or even completely bleached white (e.g., Figs. 4 A, B ; 9 A, C ; 11 A ; 14 A ; 15 A, B ; 20 B ; 22 C, D ; 27 B ). Fading and bleaching is a common process in museum specimens especially after a long period of time; another remarkable example of color loss in preserved specimen was presented by Pietsch et al. (2009). This process can be accelerated by poor preservation, exposition to light or chemicals (pers. obs.).

The holotype of P. albeolus is also contorted and the tip of the snout seems to be broken. Although Prokofiev and Kukuev (2008: 76) argue that the specimen is not decalcified, their description of soft musculature and very movable skin clearly indicates that was not properly preserved. In such conditions, it is very likely to observe differences of morphometrics and that some photophores of the mdf might have been lost. Even though P. albeolus was described from a single specimen with uncertain locality, Prokofiev and Kukuev (2008: 75) proposed a series of evolutionary facts that caused the fixation of “aberrant features”, and that the species might be “circumglobally distributed in the Antarctic waters” (p. 76).

I am very skeptical about the characteristics used to diagnose P. albeolus . Besides the bleaching, the contorted body and broken snout easily justifies the differences of morphometrics, and the loose skin, the partially missing mdf photophores and rough appearance of head. Similar losses are found in the holotype of P. cephalus . It seems to be even more difficult to accept the broad species distribution and the proposed evolution events, without any other known specimen. Considering those arguments and the lack of evidence about the validity of such species, Pseudoscopelus albeolus is herein a placed in synonymy of P. australis .

Figures

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 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 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 11. Pseudoscopelus obtusifrons: (A) USNM 93141, 93.3 mm, holotype; B) HUMZ 130746, 118.6 mm; (C) USNM 268429, 115.2 mm (notice rtf photophores along body); (D) NMNZ P. 20074, 100.7 mm, lateral view of head with anterior teeth of premaxilla and dentary evident; and (E) NMNZ P. 20074, 100.7 mm, ventral view of body, with lvf indicated by arrows.

FIGURE 14. Pseudoscopelus cordilluminatus: (A) MCZ 161017, 77.0 mm, holotype; (B) CAS 223102, 88.7 mm, paratype.

FIGURE 15. Pseudoscopelus altipinnis: (A) YPM 2798, 185.8 mm, holotype; (B) USNM 93139, 122.7 mm, holotype of P.microps.

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 22. Pseudoscopelus aphos: (A) USNM 296957, 71.9 mm; (B) USNM 296948, 58.6 mm, detail of internal pigmentation of mouth. Pseudoscopelus parini: (C and D) NMNZ P. 24463, 100.8 mm, in lateral and ventral views.

FIGURE 23. Map of distribution of (A) Pseudoscopelus aphos (diamond), P. lavenbergi (cross), and P. parini (circle); (B) P. astronesthidens (cross), P. australis (asterisk), and P. odontoglossum (star). Each symbol may represent more than one locality; solid symbols represent type localities.

FIGURE 24. Pseudoscopelus astronesthidens: (A) MCZ 163443, 71.8 mm. Pseudoscopelus australis: (B) NMNZ P. 40787, 197.4 mm. Pseudoscopelus odontoglossum: (C) SIO 61-48, 70.2 mm, holotype

FIGURE 25. Schematic drawing of the photophore pattern in lateral and ventral views of (A) Pseudoscopelus astronesthidens, MCZ 163443, 71.8 mm; (B) P. australis, NMNZ P. 40787, 197.4 mm. Dashed lines indicate level of anus.

FIGURE 27. Pseudoscopelus lavenbergi: (A) LACM 30573-1, 86.3 mm, paratype; (B) CAS 61407, 63.0 mm, paratype.