DESCRIPTIONS OF PREZOEAE AND STAGE I ZOEAE OF 

 CHIONOECETES BAIRDI AND C OPILIO 

 (OXYRHYNCHA, OREGONIINAE) 



Evan Haynes' 



ABSTRACT 



Prezoeae and stage I zoeae of Chionoecetes bairdi and C. opilio from larvae of known 

 parentage are described. The prezoeae of the two species are essentially identical, and 

 the stage I zoeae differ only in minor detail. The larvae are similar to others of the 

 subfamily Oregoniinae but are separable from them by slight differences in morphology 

 and size. 



Snow crabs, genus Chionoecetes, are fished com- 

 mercially in Bristol Bay, Alaska, by three na- 

 tions — the United States, the Soviet Union, and 

 Japan. Catches of snow crabs in Bristol Bay by 

 all three nations have increased markedly in 

 recent years and in 1970 totaled nearly 85 mil- 

 lion pounds. Most of the catches consist of C 

 bairdi Rathbun, but some C. opilio (O. Fabricius) 

 are caught also. In 1968 the National Marine 

 Fisheries Service began an intensive investiga- 

 tion into the biology of the snow crabs in Bristol 

 Bay, which includes studies on the early life 

 history stages, especially larval distribution 

 and abundance. Positive identification of larvae 

 of C. bairdi and C. opilio is important in these 

 studies. 



The morphology of prezoeae and stage I zoeae 

 of C. bairdi and C. opilio (subfamily Oregoni- 

 inae) from the Bering Sea are described in this 

 report. The larval forms of the two species are 

 so similar that only the larvae of C. bairdi are 

 described in detail; for C. opilio, only those 

 morphological features that differ from C. bairdi 

 are described. Larvae of the two species from the 

 Bering Sea are compared with larvae of the 

 same subfamily from the North Pacific Ocean. 



MATERIALS AND METHODS 



During a National Marine Fisheries Service 

 trawling survey for snow crabs in Bristol Bay 



in May 1970, I obtained two females of C. 

 bairdi and two of C. opilio that were releasing 

 larvae. The C bairdi were caught May 9 in 

 55 fathoms at lat. 55°22'N, long. 164°35'W. Their 

 carapace widths (greatest width excluding 

 lateral spines) were 99 mm and 105 mm. One 

 of the C. opilio (77-mm carapace width) was 

 caught May 9 in 51 fathoms at lat. 55°40'N, 

 long. 164°37'W, and the other (82-mm carapace 

 width) was caught May 12 in 46 fathoms at 

 lat. 56°01'N, long. 162°25'W. My identification 

 of the two species is based on characters used 

 by Garth (1958). 



Larvae were obtained in the following man- 

 ner. Each gravid female was kept in about 20 

 liters of filtered sea water with a temperature 

 of about 2.5 °C. Hatching began immediately, 

 and the first samples, which consisted mostly 

 of prezoeae, were taken after about 2 h. Other 

 samples were collected about 24 h later, when 

 most of the larvae had molted to stage L Only 

 prezoeae and stage I zoeae were obtained 

 because it was not practical to keep the zoeae 

 alive at sea long enough to allow molting to the 

 next zoeal stage. The larvae were preserved in a 

 5% solution of Formalin'^ and sea water. 



Drawings of whole animals and appendages 

 (Figures 1 and 2) were made from preserved 

 specimens cleared in lactic acid; the illustra- 

 tions were prepared with the aid of a camera 



' Auke Bay Fisheries Laboratory, National Marine 

 Fisheries Service. NOAA, Auke Bay, AK 99821. 



Manuscript accepted November 1972. 

 FISHERY BULLETIN: VOL. 71, NO. 3, 1973. 



^ Reference to trade names does not imply endorse- 

 ment by the National Marine Fisheries Service, NOAA. 



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