Host utilization during ontogeny by two pycnogonid species (Tanystylum duospinum and Ammothea hilgendorfi) parasitic on the hydroid Eucopella everta (Coelenterata: Campanulariidae)

The calyptoblast hydroids Aglaophenia struthionides (Murray, 1860), Eucopella (= Campanularia) everta (Clark, 1896), and Abietinaria spp. in the low intertidal zone at Mussel Point, Pacific Grove, Monterey Bay, California, often bear the adult pycnogonids Tanystylum duospinum Hilton, 1939 and Ammothea hilgendorfi (Böhm, 1879). Larval stages of these pycnogonids were found living and feeding on Eucopella everta. The larvae of Tanystylum duospinum are ectoparasitic. Those of Ammothea hilgendorfi are endoparasitic in the gastrovascular cavities of hydranths. Larvae of both species feed on the gut contents of Eucopella everta, often on the same hydroid colony.