Raja binoculata Girard, 1854

David A. Ebert & Chante D. Davis, 2007, Descriptions of skate egg cases (Chondrichthyes: Rajiformes: Rajoidei) from the eastern North Pacific., Zootaxa 1393, pp. 1-18: 10-11

publication ID


publication LSID


persistent identifier


treatment provided by


scientific name

Raja binoculata Girard, 1854


Raja binoculata Girard, 1854  ZBK 

Description: The egg cases of Raja binoculata  ZBK  (Figure 8) are perhaps the most distinctive skate egg case found in the ENP. The dorsal surface is convex with two prominent ridges; no other known ENP skate egg case has these ridges. These are very large egg cases, 210 to 280 mm in length from anterior to posterior apron borders, with a MAW about 52% of ECL. Egg case surface very smooth, without striations or fibrous covering. Under magnification the surface appears smooth and without striations. LKW very broad, about 30-33% of MAW, narrowing to about 4-6% at MIW, and extending length of egg case including outer edge of horns; keels also along inner edge of horns. Attachment fibers not present. Anterior apron border broad, slightly concave, fraying along edge, anterior horns about 28-30% of ECL, curving dorsally, with tips flattening and curling toward egg case. Posterior apron broad, transverse, and fraying at edge, its width less than that of anterior. Posterior horns short, stout, about 32-38% ECL, horn base width about 24% of horn length; horns curved, and flattening towards tips. Lateral keels extend beyond horn length. Color of egg case after preservation a dark brown to greenish brown.

Remarks: The egg case of R. binoculata  ZBK  is perhaps the largest egg case of any known skate species, with a maximum known length, excluding horns, exceeding 300 mm (Hitz, 1964). Raja binoculata  ZBK  is the only skate species, except for R. pulchra Liu, 1932  ZBK  , known to have multiple embryos per egg case. These skates may have 2-7 embryos, with an average of 3-4 per egg case (Hitz, 1964). The Japanese endemic R. pulchra  ZBK  is known to have 1-5 embryos per egg case (Ishiyama, 1958b). Although it has not been studied in detail, increased fecundity, due to multiple oviparity, in these species may have significant conservation implications. Raja binoculata  ZBK  is known to produce up to 360 egg cases per year in captivity (Kevin Lewand, Monterey Bay Aquarium, pers. comm.). Assuming an average of 3.5 embryos per egg case the annual fecundity may reach 1,260 neonates, or more, making it one of the most fecund of all elasmobranchs.

Material examined: CAS 224341, northern California (38.033 N, - 123.1237 W), 78 m, 24 September 2004  ; MLML RB 102403-4-06, 146.7 cm TL, central California (36.4076 N, - 121.5276 W), 69 m, 22 October 2003  ; MLML EX 58, southern Oregon (44.311 N, - 124.257 W), 71 m, 4 September 2004  .


USA, California, San Francisco, California Academy of Sciences