Biology of Fabia subquadrata — Pearce 
33 
4. The external manifestations of ecdysis in 
F. subquadrata are described. 
5. Copulation occurs in open water, with both 
the male and female crabs leaving their sym- 
biont host as the hard, Stage I instar. Following 
copulation the female crabs return to a host or- 
ganism to continue their development. Some, if 
not all, surviving males return to a host. 
6. Only during the copulatory swarming have 
males and females been found together. Only 
three multiple infestations of the host have been 
noted; two of these were between two males 
and the third was between probably incom- 
patible stages of a male and female. 
7. Copulatory swarming occurs in Puget 
Sound during late May. This is followed by a 
period of 21-26 weeks, during which the pre- 
cociously inseminated females pass through the 
five posthard developmental instars. Ovigerous 
females are first noted in November; the eggs 
hatch in February. 
8. The growth rate of F. subquadrata ap- 
pears to be positively correlated with the growth 
rate of the definitive host, the horse mussel, 
Modiolus modiolus . Suggestions are given to ex- 
plain the fact that immature crabs are less com- 
monly associated with the relatively larger host 
mussels. 
9. Four new bivalve hosts are given for F. 
subquadrata. 
10. Evidence is presented which suggests that 
the mussel crab is a true parasite causing exten- 
sive physical damage to the host organism. 
11. Crabs found in mussels removed from 
deeper waters tend to be smaller than those re- 
moved from hosts taken in relatively shallow 
waters. 
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