Bathyraja microtrachys ( Osburn & Nichols, 1916 )

Ebert, David A. & Davis, Chante D., 2007, Descriptions of skate egg cases (Chondrichthyes: Rajiformes: Rajoidei) from the eastern North Pacific, Zootaxa 1393, pp. 1-18 : 6-7

Bathyraja microtrachys ( Osburn & Nichols, 1916)

Description: The egg cases of Bathyraja microtrachys ( Figure 5) are small, 79 to 81 mm in length, with MAW about 63–64% of ECL. The egg case surface is coarsely striated, with irregular rasp­like denticles, making its texture very rough to the touch. LKW is very narrow, <5% of MAW and not extending onto horns. Anterior apron border of egg case broad, deeply concave, anterior horns robust at base, but flattening towards tips and becoming thread­like, tips curving dorsally and back towards egg case. Posterior apron is nearly straight, broad, and transverse, width similar to anterior. Posterior horns robust at base, very long, about 66% length of anteriors and about 1.1 times ECL, curved inwards, each tapering to a thread­like tip. Attachment fibers present, extending length of lateral keel. Egg cases removed from a single preserved specimen were a dark golden brown.

Remarks: This is the first confirmed record, and description, of the egg case of this species. The egg cases described here were removed in utero from a 62.8 cm TL specimen (SIO 8780). Cox (1963: Figure 7 ) suggested that the egg case he described and illustrated as B. trachura may eventually prove to be this species. However, the term embryo that was removed from that egg case (CAS 25617), and described below, appear to be that of B. spinossisima ( Ebert, 2005) .

Until recently this species had been considered a synonym of B. trachura ( Ebert, 2003) . However, examination of the holotypes of B. microtrachys and B. trachura by the senior author, plus additional material confirm that these species are distinct. To further separate these two species their egg cases can be used to distinguish them from each other. The egg case of B. microtrachys differs from that of B. trachura in that the former has very narrow lateral keels and a coarsely striated surface texture that is rough to the touch, while the latter has very broad lateral keels and is smooth to the touch.

Bathyraja microtrachys is one of the deepest occurring skate species, known to occur down to at least 3,100 m (unpublished data). The shallowest record of this species is the holotype known from 1,995 m. All other records of it have come from depths greater than 2,000 m.

Material examined: SIO 8780, 62.8 cm TL, off Waldport, Oregon (44.4130 N, ­ 125.3410 W), 2850 m, 6 February 1987.

Figures

FIGURE 7. Egg case of Bathyraja trachura. Arrow denotes crossbar (broken). Scale bar 20 mm.