dorsal-fin spine first dorsal fin
second dorsal fin spiracle eye caudal keel nostril
caudal fin
gill slits mouth clasper anal fin pelvic fin (male)
pectoral fin General Anatomy of Skates
Dorsal scapular thorns (S)
nuchal thorns (N) mid-dorsal thorns (D) malar hooks
tail thorns dorsal fins rostral thornlets
caudal fin Skate Clasper orbital thorns (O) interdorsal thorns clasper (male) spiracle cloaca pseudosiphon
ventral lobe
dorsal lobe alar hooks pelvic fin
gill slits Ventral pectoral fin
7 8 General Anatomy of Egg Cases
Egg Case Dorsal View byssal threads byssal threads byssal threads attached at attached at attached at mid-case posterior byssal threads anterior margin margin attached on anterior horns
byssal threads attached on posterior horns
anterior horns anterior posterior posterior horns margin margin
Egg Case Lateral View anterior horns (with dorsal curl) dorsal surface case length mid-case width mid-case keel (includes keels) keel width
ventral surface posterior horns Key to the Sharks, Skates, and Ratfish of Alaska
1 One gill slit on each side of head, covered by an opercle...... page 18 Spotted ratfish (Hydrolagus colliei) Gill slits 5-7, on sides or underside of head 2
2 (1) Body not flattened, nearly round in cross section; pectoral fins not enlarged or fused with head; gill openings on side of head Sharks 3 Body distinctly flattened; pectoral fins large and fused with head, giving the body a disc shape; gill openings on underside of head Skates 11
3 (2) Anal fin absent 4 Anal fin present 5
4 (3) Single spine at front of each dorsal fin; pectoral fins large and pointed; caudal fin with two distinct lobes ...... page 20 Spiny dogfish (Squalus acanthias) No spine at front of dorsal fins; pectoral fins small and rounded; caudal fin without distinct lobes...... page 22 Pacific sleeper shark (Somniosus pacificus)
5 (3) Gill slits 6; single dorsal fin...... page 24 Bluntnose sixgill shark (Hexanchus griseus) Gill slits 5; two dorsal fins 6
6 (5) Gill slits highly elongate, extending from dorsal surface of head nearly to ventral midline of body; teeth very small, with flattened, posteriorly directed cusp...... page 26 Basking shark (Cetorhinus maximus) Gill slits restricted to side of head; teeth relatively large, sharp, with one or more cusps 7
9 Key to the Sharks, Skates, and Ratfish of Alaska 10
7 (6) Front of first dorsal fin posterior to front of pelvic fins; caudal fin weakly developed; maximum length less than 70 cm...... page 28 Brown cat shark (Apristurus brunneus) Front of first dorsal fin anterior to front of pelvic fins; caudal fin well developed; maximum length greater than 70 cm 8
8 (7) Caudal fin extremely heterocercal, with upper lobe many times length of lower lobe; teeth without serrations or cusps...... page 30 Thresher shark (Alopias vulpinus) Caudal fin not extremely heterocercal; teeth with serrations or cusps 9
9 (8) Pectoral fin, head, and body long and narrow; two posterior-most gill slits above pectoral-fin base; caudal fin distinctly heterocercal...... page 32 Blue shark (Prionace glauca) Pectoral fin, head, and body short and robust; all gill slits anterior to pectoral-fin base; caudal fin nearly homocercal 10
10 (9) First dorsal-fin base almost directly above pectoral-fin base; teeth with lateral cusps, not serrate; secondary lateral keel on caudal peduncle...... page 34 Salmon shark (Lamna ditropis) First dorsal-fin base almost entirely posterior to pectoral-fin base; teeth without lateral cusps, serrate; no secondary lateral keel on caudal peduncle...... page 36 Great white shark (Carcharodon carcharias)
11 (2) Snout firm to tip; pectoral-fin rays fall distinctly short of tip of snout 12...... (Amblyraja and Raja) Snout flexible, especially near tip; pectoral-fin rays nearly reach tip of snout 14 ...... (Bathyraja)
12 (11) Two or three pairs of scapular thorns; small rostral thorns (thornlets) present on dorsal surface near tip of snout...... page 38 Roughshoulder skate (Amblyraja badia) Scapular thorns and rostral thorns absent 13 13 (12) Posterolateral margin of pelvic fin slightly concave; base of pectoral fin with large ocellus surrounded by ring of light spots; ventral surface nearly white; body diamond-shaped...... page 40 Big skate (Raja binoculata) Posterolateral margin of pelvic fin deeply notched; base of pectoral fin with ring of dark pigment; ventral surface dark; body diamond-shaped, with elongate snout...... page 42 Longnose skate (Raja rhina)
14 (12) Scapular thorns present (may be reduced) 15 Scapular thorns absent 18
15 (14) Denticles absent from area surrounding tail thorns; orbital thorns present (but often obscure) 16 Denticles present in area around and between tail thorns; orbital thorns absent 17
16 (15) Dorsal surface generally brown, often with a few light spots or blotches; total midline thorn count typically 32 or less ...... page 44 Alaska skate (Bathyraja parmifera) Dorsal surface olive green with many dark spots or blotches and brighter yellow patches; total midline thorn count typically 31 or more...... page 46 “Leopard skate” (Bathyraja sp. cf. parmifera)
17 (16) Mid-dorsal row of thorns usually interrupted; tail thorns reduced along length of tail, 0-2 reduced thorns between dorsal fins; dorsal surface brown; clasper without pseudosiphon...... page 48 Bering skate (Bathyraja interrupta) Mid-dorsal row of thorns continuous (may be worn down in older specimens); tail thorns not reduced along length of tail, 1-2 strong thorns between dorsal fins; dorsal surface gray; clasper with pseudosiphon...... page 50 Aleutian skate (Bathyraja aleutica)
Key to the Sharks, Skates, and Ratfish of Alaska 11 Key to the Sharks, Skates, and Ratfish of Alaska 12 18 (14) Ventral surface typically creamy white; dorsal surface uniform brown or brown with pale, yellow, or green and black blotches; disc with thorns absent; median tail thorns weakly developed and progressively smaller toward tip of tail 19 Ventral surface dusky, dark, or blotchy; dorsal surface uniformly dark or dark with light blotches; disc with or without thorns; median tail thorns generally well developed along entire length of tail 21
19 (18) Dorsal surface of disc dull brown with black spots and blotches (no pale, yellow, or green blotches); denticles unevenly distributed on disc, often leaving bare patches; tail length less than or equal to precaudal length...... page 52 Okhotsk skate (Bathyraja violacea) Dorsal surface of disc usually with at least two pale or yellowish spots near pelvic fins, often with complex pattern of bright yellow or olive-green spots and blotches; denticles fine, dense, and evenly distributed on disc; tail length greater than or equal to precaudal length 20
20 (19) Disc small and rounded; dorsal coloration brown, usually with variable pale and black blotching, including a pale round ocellus near each pelvic-fin base; tail may have yellow blotches; clasper with pseudosiphon...... page 54 Mud skate (Bathyraja taranetzi) Disc of moderate size and triangular; dorsal coloration brown to olive-green with extensive yellow blotching and smaller black spots, including a large irregularly shaped yellow blotch near each pelvic-fin base; tail with distinct yellow band near base; clasper without pseudosiphon...... page 56 Butterfly skate (Bathyraja mariposa)
21 (18) Ventral surface of disc and tail covered with fine denticles; snout somewhat elongate ...... page 58 Deepsea skate (Bathyraja abyssicola) Ventral surface of disc and tail smooth, without denticles; snout not elongate 22 22 (21) Mid-dorsal thorns present and strong...... page 60 Commander skate (Bathyraja lindbergi) Mid-dorsal thorns absent 23
23 (22) Nuchal thorns absent; dorsal and ventral surfaces uniformly dark brown to black, except for white patches often present around mouth and cloaca...... page 62 Roughtail skate (Bathyraja trachura) Nuchal thorns present (rarely absent); dorsal surface usually with light blotches on disc or white patches between eyes; ventral surface dusky or blotchy to dark brown 24
24 (23) Nuchal thorns weak, 1-3 (rarely absent); dorsal surface uniformly gray-brown to dark brown, usually with white patches between eyes; ventral surface medium brown, usually with white patch around mouth and/or cloaca...... page 64 Whitebrow skate (Bathyraja minispinosa) Nuchal thorns moderate, 1-7; dorsal surface gray with white blotches; ventral surface of disc dusky or blotchy, with dark tail typically separated from lighter disc by a distinct line...... page 66 Whiteblotched skate (Bathyraja maculata)
Key to the Sharks, Skates, and Ratfish of Alaska 13 14 Key to Egg Cases of Alaska Chondrichthyans
1 Case elongate, spindle or club shaped, without pair of horns at each end...... page 18 Spotted ratfish (Hydrolagus colliei) Case ellipsoid to rectangular, with pair of horns at each end 2
2 (1) Case ellipsoid, small, length less than 60 mm; anterior horns with elongate tendrils; posterior horns short ...... page 28 Brown cat shark (Apristurus brunneus) Case rectangular, length greater than 60 mm; anterior horns without elongate tendrils; posterior horns short to long 3
3 (2) Case length more than 200 mm; length of any horn less than 1/4 mid-case width ...... page 40 Big skate (Raja binoculata) Case length less than 165 mm; length of any horn more than 1/4 mid-case width 4
4 (3) Posterior horns short, less than half of mid-case width, never overlapping; case width more than 100 mm; case smooth...... page 42 Longnose skate (Raja rhina) Posterior horns long, more than half of mid-case width; case width less than 100 mm; case with low longitudinal ridges or bristly, fuzzy, or furry texture 5
5 (4) Case with rows of longitudinal spines creating heavily textured surface; keel narrow and indistinct 6 Case with rows of low longitudinal ridges creating smoothly ridged texture; keel wide and distinct 10 6 (5) Case length less than 77 mm, width less than 60 mm; case with longitudinal spinous rows creating rough rasp-like texture...... page 64 Whitebrow skate (Bathyraja minispinosa) Case length more than 80 mm, width more than 50 mm; case with longitudinal spinous rows creating fuzzy or furry texture 7
7 (6) Case length less than 100 mm; case width less than 65 mm 8 Case length more than 110 mm; case width more than 70 mm 9
8 (7) Case with rows of short saw-like spines arranged in continuous bands...... page 60 Commander skate (Bathyraja lindbergi) Case with rows of elongate slender conical spines with bifid tips...... page 66 Whiteblotched skate (Bathyraja maculata)
9 (7) Byssal threads attached on posterior horn; mid-case keel thick, dark, opaque ...... page 50 Aleutian skate (Bathyraja aleutica) Byssal threads attached even with posterior margin; mid-case keel thin, brown, translucent...... page 58 Deepsea skate (Bathyraja abyssicola)
10 (5) Case length more than 100 mm; case width more than 75 mm 11 Case length less than 100 mm; case width less than 75 mm 13
11 (10) Keel ending abruptly on mid-anterior horns; all horns slender and smooth with loose curl ...... page 38 Roughshoulder skate (Amblyraja badia) Keel extending entire length of anterior horns; all horns flat and wide; anterior horns with tight curl 12
12 (11) Byssal threads attached on anterior horn distal to anterior margin of case...... page 44 Alaska skate (Bathyraja parmifera) Byssal threads attached at anterior margin of case...... page 46 “Leopard skate” (Bathyraja sp. cf. parmifera)
Key to Egg Cases of Alaska Chondrichthyans 15 Key to Egg Cases of Alaska Chondrichthyans 16
13 (10) Anterior horns curling ventrally; keel width approximately equal to horn width at mid-posterior horn...... page 62 Roughtail skate (Bathyraja trachura) Anterior horns curling dorsally; keel width less than horn width at mid-posterior horn 14
14 (13) Anterior horns slender with loose curl; keel absent on anterior horns; case length less than 75 mm 15 Anterior horns wide with tight curl; keel prominent on anterior horns; case length more than 75 mm...... page 48 Bering skate (Bathyraja interrupta) or page 52 Okhotsk skate (Bathyraja violacea)
15 (14) Case width less than 50 mm; keel width at mid-case 3 mm or less ...... page 54 Mud skate (Bathyraja taranetzi) Case width more than 55 mm; keel width at mid-case 4 mm or more...... page 56 Butterfly skate (Bathyraja mariposa)