Biology of Fabia subquadrata — -PEARCE 
distinguish between adult and "early” male 
stages, although this distinction is not evident 
in the summary of their experimental results. 
The hypothesis that the invasive stage F. sub- 
quadrata is selectively attracted to the immature 
spat of the host mussel is made more plausible 
in the light of recent evidence presented by 
Blake (I960). He has found that the predator 
oyster drill, Urosalpinx, is attracted selectively 
to its prey, Crass os trea virginica and Modiolus 
21 
demissus, on the basis of oxygen consumption 
(used as an index of metabolic activity). One 
of four factors affecting the metabolic rate was 
the age of the prey (the others were species, 
growth rate, and feeding). Both Haskin (1950) 
and Carriker ( 1955:49) have shown that there 
is a predilection by the drills in their choice of 
younger prey. It is hoped that further investiga- 
tion of this aspect of the relationship between 
F. subquadrata and M. modiolus can be made in 
a. 
D 
o 
o: 
i i i l ill ii i s 
cvJro ^ in (p n- co a) O 
LENGTH GROUPS OF MUSSELS-MM 
Fig. 5. Histogram showing percent of first true crab stage ( stippled fraction of bars), immature females 
of all stages ( horizontal lines), males ( fine oblique lines), and Stage V females ( heavy oblique lines) found 
in each length group of the host mussel, M. modiolus. 
