Bathyraja spinosissima (Beebe & Tee-Van, 1941)

Knuckey, James D. S. & Ebert, David A., 2022, A taxonomic revision of Northeast Pacific softnose skates (Rajiformes: Arhynchobatidae: Bathyraja Ishiyama), Zootaxa 5142 (1), pp. 1-89 : 40-44

Bathyraja spinosissima (Beebe & Tee-Van, 1941)

Figures 30–33 ; Tables 6 , 8

Pacific White Skate

Psammobatus spinosissima Beebe & Tee-Van, 1941: 259 , Pl. 2 (fig. 4) [Zoologica, Scientific Contributions of the New York Zoological Society] v. 26. Holotype: CAS-SU 46500 [ex NYZS 6132 ] (embryo). Type catalog: Mead 1958: 134. 60 miles south of Cocos Island , eastern Pacific , 4°50'N, 87°00'W, depth 765 fathoms.

Psammobatis spinosissima: Beebe & Tee-Van, 1941: 259 , pl. 2, fig. 4.

Bathyaraja spinosissima: Stehmann, 1986: 263 ; McEachran, 1995: 776 (listed); Castro-Aguirre & Espinosa Pérez, 1996: 28 (listed); McEachran & Dunn, 1998: 286 (listed); Dolganov, 1999: 429 (listed); Compagno, 1999: 488 (listed); Sheiko & Fedorov, 2000: 15; Hoff, 2002: 145; Ebert, 2003: 201–202 (description, distribution); Fedorov et al., 2003: 19; Stehmann, 2005b: S35, S53; Ebert & Compagno, 2007: 117 (listed); Ebert & Davis, 2007: 8–9 (egg case description); McCosker & Rosenblatt, 2010: 188 (listed); Parin et al., 2014: 34 (listed); Dyldin, 2015: 66 (listed); Del Moral-Flores et al., 2016: 110; Weigmann, 2016: 97 (listed); Last et al., 2016: 27, 420 (figure, listed); Ebert et al., 2017: 21, 59, 68 (description, distribution, key, listed); Ehemann et al., 2018: 24; Salinas-de-León et al., 2018: 1; Burton & Lea, 2019: 99 (figure); Orr et al., 2019: 39.

Diagnosis. Large skates (2,003 mm TL), disc length and width large (44.1–56.9 and 50.6–67.3% TL, respectively), pectorals possess rounded apices, head moderately long (14.0–20.5 % TL), interspiracular length large (9.1–12.2% TL), mouth width large (6.1–13.0% TL); mature claspers have not been described; teeth in 31–33 and 24–31 rows on upper and lower jaw, respectively; total vertebrae 137; dorsal and ventral surfaces covered with prickles; thorns generally absent on dorsal surface, tail thorns present (22–28), interdorsal thorns weakly developed or absent (0–1), middorsal, nuchal, and scapular thorns absent; dorsal coloration pale white to grey; outer edges of pectorals darker in coloration; ventral coloration pale white.

Description. A very large sized skate with a rhomboidal disc, 1.2–1.3 times as broad as long; the disc length large 44.1–56.9% TL; disc width large 50.6–67.3% TL; straight to moderately convex beside and forward of eyes; apex broadly rounded; posterior margin slightly convex; free rear tip broadly rounded. Head length moderate 14.0– 20.5 % TL; preorbital snout length 6.1–12.8% TL; preoral length 9.1–12.3% TL. Snout tip pointed, possessing no fleshy process at apex. Eye length moderate 2.3–5.0% TL; interorbital width large 4.9–9.5% TL. Spiracles relatively small 1.2–2.3% TL, oval shaped; interspiracular length large 9.1–12.2% TL. Mouth width very large 6.1–13.0%. Nasal curtain length and width both moderate, 2.4–3.5% TL and 6.1–11.8% TL, respectively, its posterior margin fringed at the corners; anterior margin of curtain lobe-like. Internarial distance long 7.3–11.3% TL; first gill slit length 1.2–2.0% TL; fifth gill slit length 0.6–2.0% TL; distance between gill slits large, distance between first gill slits 15.9–24.0% TL, and distance between fifth gill slits 11.0–15.4% TL. Upper jaw moderately well arched, possessing a symphysis; lower jaw convex. Teeth similar in both jaws; teeth unicuspid, with a strong, bluntly pointed posteriorly directed cusp; arranged in longitudinal rows; teeth relatively high in number and similar in number, upper teeth (31–33) and lower teeth (24–31).

Pelvic fins moderate; anterior lobe relatively short 4.3–7.9% TL, posterior lobe 9.0–12.2% TL, and similar between sexes and maturities, inner margin incised. Tail relatively moderately sized 47.3–66.5% TL, stout, wider at base, tapering to the first dorsal fin origin, not expanded in the middle. Dorsal fins small in size, second dorsal fin taller than first dorsal fin, 1.1–1.8% TL and 0.9–1.8% TL, respectively; dorsal fin lengths similar, 2.4–4.3% TL and 2.7–3.0% TL, for the first and second dorsal fins, respectively; anterior margins of both fins concave, apices rounded; free rear tip rounded; interdorsal space short 0.4-0.6% TL; rear tip of first dorsal fin not overlapping base of second dorsal fin. Caudal fin relatively long, base length 4.4–5.5% TL; its dorsal margin weakly concave; connected to second dorsal fin by a small membranous ridge.

Dorsal surface covered with prickles and some thorns; ventral surface covered in small prickles. Tail thorns present (22–28) and moderate in size; interdorsal thorns weakly developed and occasionally absent (0–1); middorsal, nuchal, and scapular thorns absent. Thorns in a single, non-continuous row; no multiple rows of thorns on body. As no mature males were included in this study, number of alar or malar thorn counts is unknown. Based on congener species, malar thorns are unlikely to be present in this species.

Mature males were not available during the course of this study, so clasper descriptions are currently unavailable.

Dermal denticles possess 4–5 base points and are well-developed on the posterior third of the dorsal surface; denticles on the first dorsal fin thick, straight, posteriorly-oriented; denticles on head stouter than dorsal fin; found in high density patches ( Figure 34 ).

Coloration. Dorsal coloration pale white to light grey; outer edges of pectorals slightly darker in coloration. Ventral coloration pale white. Thorns on dorsal surface pale. Coloration after preservation is a uniform light brown on both the dorsal and ventral surfaces.

Egg case description. Egg cases large compared to its congeners (92 mm TL), plum brown in color, longitudinally weakly striated. Both surfaces of the case are plush-like to the touch. Horns present, posterior horns curve inwards, and narrow at tips ( Ebert & Davis, 2007).

Distribution. Bathyraja spinosissima is a wide spread species and has been confirmed as occurring in the North Pacific, specifically from the Bering Sea, south to the Galapagos Islands and Costa Rica ( Ebert, 2003; Orr et al., 2019). It occurs at depths of 800–2,938 m ( Ebert 2003).

Biological notes. Size at maturity is unknown for males; female specimens in this study were found to be mature at 98 cm TL. Size at birth is 25 cm TL ( Ebert, 2003). Maximum size is at least 2 m TL ( Ebert, 2003). The species is a predator of deep-water benthic fishes ( Ebert, 2003).

Habitat. Inhabits deep waters to almost 3,000 m, making it one of the deepest dwelling skates encompassed in this study ( Ebert, 2003), Reported to prefer cold temperatures compared to its congeners ( Kuhnz et al., 2019).

Etymology. The species name comes from the Latin spinosus, meaning thorny. It was named thus for the prickles on both the ventral and dorsal surface.

Comparisons. Bathyraja spinosissima is the most easily identifiable softnose skate in the ENP, mostly due to its large size and coloration. Interspiracular length, mouth width, and internarial distance are significantly larger than all of its congeners (F 6,104 = 4.7, p = 0.0003, F 6,104 = 9.7, p <0.0001 and F 6,104 = 21.9, p <0.0001, respectively). Furthermore, smaller-bodied skates in the region (e.g., B. interrupta , B. kincaidii , B. microtrachys , and B. trachura ) lack the pale dorsal surface coloration that B. spinosissima possesses.

The two other large skates in the same geographic range, Bathyraja abyssicola and B. aleutica , are easily differentiated by the dark brown dorsal coloration that the two species display and by the fact that both species possess middorsal and nuchal thorns, which B. spinosissima lacks. Furthermore, B. spinosissima has significantly longer internarial and interspiracular widths than B. abyssicola and B. aleutica .

Remarks. The species appears to prefer rockier habitat than its congeners, as it has been documented over rocky substrate ( Kuhnz et al., 2019). The preference for rocky substrate may account for why no fresh specimens were captured for this study. The study utilized bottom trawl, which does not work on highly rugose surfaces. Observations from remotely operated vehicles show that this species prefers to swim at slow speeds several meters above the seafloor ( Kuhnz et al., 2019). This species has been witnessed to use deepsea vents for incubating it egg cases, making it the first reported example of a chondrichthyan using volcanic activity for the purposes of incubation ( Salinas-de-León et al., 2018).

Figures

FIGURE 30. Bathyraja spinosissima, dorsal view, fresh. Photo by Dan Kamikawa (NOAA). Scale bar = 100 mm.

FIGURE 31. Bathyraja spinosissima, ventral view, fresh. Photo by Dan Kamikawa (NOAA). Scale bar = 100 mm.

FIGURE 32. Bathyraja spinosissima, holotype, CAS 25617, 164 mm TL, prenatal male, dorsal view, preserved. Photo by D.A. Ebert. Scale bar = 50 mm.

FIGURE 33. Ventral view X-radiograph of Bathyraja spinosissima, holotype, CAS 25617, 164 mm TL, prenatal male. X-radiograph by Jon Fong (CAS).

FIGURE 34. Scanning electron microscope images of the dermal denticles of Bathyraja spinosissima from A. the first dorsal fin and B. the head region, behind the eyes. Photos by Justin Cordova (MLML).