Bathyraja trachura ( Gilbert, 1892 )

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 : 9-10

Bathyraja trachura ( Gilbert, 1892)

Description: The egg cases of Bathyraja trachura ( Figure 7 ) are small, 62 to 78 mm in length, with MAW about 77–97% of ECL. Egg case surfaces with prominent longitudinal striations and smooth to the touch. LKW very broad, striated, about 15–20% of MAW, and extending length of case including outer edge of horns; an inner keel is present along edge of both anterior and posterior horns. Attachment fibers present along lateral keels, originating about outer base of posterior horns. Anterior apron border broad and concave, anterior horns about one­half ECL, horns curved inwards toward median plane of egg case, tips curling towards ventral aspect of egg case, and flattening towards tips. Posterior apron nearly straight, broad, transverse, and up to 7 mm wider than posterior apron. Posterior horn length variable, 0.8 to 1.4 times ECL, horns curved inwards to median plane of egg case, and flattening towards tips. A distinct crossbar originating midway along posterior horns was present on six of nine egg case pairs. One pair had evidence of an incompletely formed crossbar and two had no evidence. This crossbar is unique among ENP skates. Color after preservation a dark brown becoming a light golden brown on keels.

Remarks: Ebert (2005) described the egg case of this species, based on material from the eastern Bering Sea, and commented that the egg case described and figured by Cox (1963) as B. trachura was not that species. The egg case figured by Cox (1963: Figure 5), and captioned as Raja stellulata , is actually that of B. trachura .

The posterior horns on some B. trachura egg cases, 75% in this study, have a unique crossbar that is not present on any of the other skate egg cases that we have examined from this region ( Figure 7 ). In some instances the crossbar was broken or missing. Whether the crossbar remains intact, or for how long, once the egg case is deposited on the seafloor is unknown as we did not obtain any egg cases of this species in situ.

Material examined: CAS 224340, 79.1 cm TL, off central Oregon (45.3862 N, ­ 125.5707 W) 924 m, 3 September 2004; MLML BT 100804 ­1­6, 86.5 cm TL, off central Oregon (45.3862 N, ­ 125.5771 W), 929 m, 3 September 2004; MLML BT 110504 ­2­3, 66.3 cm TL, off northern California (37.0453 N, ­ 120.3272 W), 1101 m, 12 October 2004; MLML BT 031105 ­04, 789 mm TL, off northern California (38.5142 N, ­ 122.6890 W), 320 m, 17 February 2005; MLML BT 011205 ­19, 78.7 cm TL, off central California (36.2502 N, ­ 122.0718 W), 366 m, 6 January 2005.

Figures

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