Mr. Crossland et al., HOST SELECTION AND DISTRIBUTION OF HYPERMASTUS PLACENTAE (EULIMIDAE),AN ECTOPARASITIC GASTROPOD ON THE SAND DOLLAR ARACHNOIDES PLACENTA (ECHINOIDEA), Australian Journal of Marine and Freshwater Research, 44(6), 1993, pp. 835-844
The intertidal sand dollar Arachnoides placenta is parasitized by the
eulimid Hypermastus placentae at Pallarenda Beach, Townsville, Queensl
and. A. placenta is the only echinoderm species in the region with whi
ch H. placentae associates. Sand dollars are distributed in an aggrega
ted pattern within the littoral zone at Pallarenda Beach, and the dist
ribution of parasites within the adult sand dollar population conforms
closely to Poisson expectations. A. placenta adults in ah size classe
s are equally susceptible to parasitization by H. placentae, whereas j
uveniles are not parasitized; host selection may be determined by a re
quirement for host gonadal tissue in the diet of the parasite. Infesta
tion rate and number of parasites per host decrease as host density in
creases. Parasite body size is not related to host body size.