THE ECTOPARASITISM OF BOONEA AND FARGOA (GASTROPODA: PYRAMIDELLIDAE)

¹ Department of Malacology, The Academy of Natural Sciences of Philadelphia, Pennsylvania 19103

1. Three Boonea species (occurring in sympatric species pairs) occupy different habitats and have different molluscan host preferences. In the field, B. seminuda is preferentially with Crepidula fornicata or Argopecten irradians, B. bisuturalis with Littorina littorea (introduced), Hyanassa obsoleta or Crassostrea virginica, and B. impressa with C. virginica. Weights of the first two species are about 0.03 to 0.17% those of their hosts. In the laboratory, B. seminuda was attracted much more to Crepidula fornicata than to Littorina littorea. With B. bisuturalis it was vice versa.

2. In the laboratory, B. seminuda fed on 22 out of the 36 gastropod and bivalve "hosts" offered; B. bisuturalis fed on 37 out of 45, and B. impressa fed on 36 out of 37. Some of these mollusks probably serve as secondary hosts in nature. Boonea definitely is not host-specific. Polychaetes, Chaetopleura and Molgula were not fed on.

3. Fargoa dianthophila and F. bartschi, two much rarer species, compete with each other for space and food by both obligately parasitizing species in the genus Hydroides, sometimes co-occurring on the same individual. Fargoa species do seem to be host-specific.