DESCRIPTION OF STAGE II ZOEAE OF 



SNOW CRAB, CHIONOECETES BAIRDI, 



(OXYRHYNCHA, MAJIDAE) FROM PLANKTON 



OF LOWER COOK INLET, ALASKA 



Chionoecetes bairdi Rathbun 1924 (subfamily 

 Oregoniinae) is the only species of snow crab 

 (genus Chionoecetes) that occurs in Cook Inlet, 

 Alaska, and contributes about 2Qf?c of the total 

 value of the commercial fisheries harvest of the 

 area (Trasky et al. 1977). The larval stages of C. 

 bairdi consist of one prezoeal, two zoeal, and one 

 megalopal stage. The zoeae are readily distin- 

 guished from known zoeae of other genera of the 

 subfamily Oregoniinae (Hyas and Oregonia) by 

 size (the zoeae of C bairdi are nearly twice as 

 large as zoeae of Hyas and Oregonia) and by 

 slight differences in morphology, especially seta- 

 tion of the antennule and length of the posterior 

 lateral spines (Haynes 1973). The prezoeae. Stage 

 I zoeae, and megalopa of C. bairdi have been de- 

 scribed from known parentage (Haynes 1973; 

 Jewett and Haight 1977). In this report, I describe 

 the Stage II zoeae from plankton and compare 

 them with other known Oregoniinae zoeae from 

 the North Pacific Ocean. 



Methods 



Stage II zoeae of C. bairdi were collected in 

 lower Cook Inlet in 1976 during a joint survey by 



the National Marine Fisheries Service and the 

 Alaska Department of Fish and Game. The C 

 bairdi zoeae were collected near the southwestern 

 tip of the Kenai Peninsula (Figure 1) in water 

 37-141 m deep. Collections were made with two 61 

 cm bongo nets fished side by side from near bot- 

 tom to surface. The nets had 0.333 mm mesh, and 

 cod end jars 0.571 mm mesh. The zoeae were cap- 

 tured by lowering the nets to about 1 m from the 

 bottom and then retrieving them vertically at a 

 velocity of slightly <1 m/s. After retrieval, zoeae 

 were washed from the nets and preserved in a 5% 

 solution of formaldehyde and seawater. 



Drawings of the Stage II zoeae (Figure 2) were 

 made from preserved specimens. The terminology, 

 methods of measurement, techniques of illustra- 

 tion, and nomenclature of appendages are 

 Haynes' (1973). Total body length includes tel- 

 sonic furcations. Setation formulae refer to setae 

 numbered from the distal to the proximal portion 

 of the appendage. Comparison of morphological 

 features was aided by first clearing the zoeae in 

 10% KOH. For clarity, setules on setae are usually 

 omitted but spinulose setae are shown. Any vari- 

 ation in setal counts is noted in text. 



Description of Stage II Zoeae 



General shape characteristic of Stage II zoeae 

 oi Chionoecetes is shown in Figure 2 A, B. Dorsal 

 and rostral spines long, tapering, essentially 



Figure l. — Sampling locations in Cook 

 Inlet, Alaska, where Stage II zoeae of 

 Chionoecetes bairdi were captured in 

 1976. 



FISHERY BULLETIN: VOL. 79, NO. 1, 1981. 



177 



