TESTER and CAREY: INSTAR IDENTIFICATION OF SPIDER CRABS 



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Carapace Width (mm) 



Figure 4.— Size-frequency histograms representing all specimens of Chionoecetes tanneri collected off the Oregon coast 1973-75 and 

 from the Gulf of the Farallons. Instars I-VII are indicated. Males are shown in solid color. 



carapaces relatively free of epifauna and lesions 

 caused by bacterial infections (Baross et al. 1978). 

 Of the 290 adult female specimens examined, 87% 

 showed exoskeleton lesions and these adult females 

 also had the highest diversity and abundance of epi- 

 fauna on their exoskeletons. Only 29% of the 124 

 adult males observed showed the effect of chitino- 

 clastic bacterial infection. No lesions or epifauna 

 were found on any of the 1,447 juveniles examined. 

 In contrast to the findings of Hartnoll (1969) who 

 worked with shallow-water spider crabs, observa- 

 tions of the carapace condition of adult male and 

 female C. tanneri suggests adult males continue to 

 molt after maturity while adult females are anec- 

 dysic, a finding consistent with Watson's (1970) data 



for C. vpilio. The unequal adult sex ratio (29% males, 

 Table 1) is also an indication that males may be sub- 

 jected to the differential mortality of continued 

 molting. 



The agreement of mean CW for adults collected 

 off the Oregon coast in the study and that of 

 Pereyra's (1966) work has an interesting corollary 

 in the material collected from near the Farallon 

 Islands. The mean carapace width of instars VI and 

 VII for C. tanneri collected west of the Farallon 

 Islands is 19.4 and 27.3 mm respectively. The cara- 

 pace widths for the same instars collected from 

 Oregon is 19.8 and 26.7 mm. Childress and Price 

 (1978) credited the constant increase in size between 

 each pair of instars in the deep-living, midwater 



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