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[[ Familiy Rajidae ]]

Key to the Eastern North Pacific Skate Egg Cases

The ENP skate egg cases can be broadly classified into two main groups: those with broad lateral keels (> 10% MAW) and those with narrow lateral keels (<10% MAW). Egg cases in the former group (with broad lateral keels) generally have a surface texture that is finely striated and smooth to the touch. Those in the latter group (with narrow lateral keels) tend to have an egg case surface that is coarse in texture, often with prickles, and is rough to the touch. The only exception in this group is the egg case of R. stellulata that differs in having a finely striated surface beneath a thick fibrous covering.

The key below includes all of the known valid skate species, plus two unidentified species, known to occur from the eastern Gulf of Alaska (ca 59° N, 138° W) southwards to the California Mexico border (ca 32° N 117° W). The validity of two species, B. obtusa (Gill & Townsend, 1897) and B. rosispina (Gill & Townsend, 1897) is questionable and the occurrence of the Alaska Skate, B. parmifera (Bean, 1881) , in the eastern Gulf of Alaska has not been confirmed from this region. The egg cases of B. parmifera , if found to occur in this area, are quite distinct. A description and illustration of the egg case of B. parmifera can be found in Ebert (2005).

1a. Lateral keel width broad,> 10% of maximum egg case width...................................................................2

1b. Lateral keel width narrow, <10% of maximum egg case width.................................................................8

2a. Egg case very large,> 180 mm....................................................................................................................3

2b. Egg case usually smaller, <100 mm...........................................................................................................4

3a. Dorsal surface distinct with two convex ridges; horns <50% ECL; keel width very broad> 30% of MAW .............................................................................................................................................. Raja binoculata ZBK

3b. Dorsal surface without convex ridges; horns> 50% ECL; keel width broad about 15 % of MAW............. ........................................................................................................ Unidentified deepsea skate species “A”

4a. Attachment fibers absent.............................................................................................................................5

4b. Attachment fibers present ............................................................................................................................ 6

5a. Lateral keel width very broad, 17-25% of maximum egg case width; posterior horns about one-half egg case length ............................................................................................................................... Raja inornata

5b. Lateral keel width broad, 12-14% of maximum egg case width; posterior horns about equal to egg case length .............................................................................................. Unidentified deepsea skate species “B”

6a. Fibrous covering absent .................................................................................................. Bathyraja trachura

6b. Fibrous covering present .............................................................................................................................. 7

7a. Fibrous covering thick, woven-like .............................................................................................. Raja rhina

7b. Fibrous covering thin ...................................................................................................... Bathyraja kincaidii

8a. Attachment fibers present ............................................................................................................................ 9

8b. Attachment fibers absent .......................................................................................... Bathyraja spinossisima

9a. Egg case with fibrous covering ............................................................................................... Raja stellulata

9b. Egg case without fibrous covering .......................................................................................... ................... 10

10a. Egg case very large,> 100 mm ................................................................................................................ 11

10b. Egg case smaller, <100 mm .................................................................................. Bathyraja mircotrachys

11a. Surface coarse, striated, with long anteriorly directed prickles giving it a velvety texture, and without a distinct groove demarcating lateral keel and egg case ..................................................... Bathyraja aleutica

11b. Surface very coarse, without anteriorly directed prickles, with a distinct groove demarcating lateral keel and egg case ................................................................................................................. Bathyraja abyssicola

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