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Abstract
The association of the scuticociliate Orchitophrya stellarum with 3 species of asteriid sea stars from the west coast of North America was studied by flushing the gonopore region with seawater and spawning the sea stars, along a latitudinal gradient of 2549 km between Pigeon Point, California, and Kodiak, Alaska. Asterias forbesii and A. rubens from the Isles of Shoals, New Hampshire (east coast), were also sampled. The ciliate was found on the aboral surface of both sexes of reproductively ripe Evasterias troschelii, Leptasterias spp., and Pisaster ochraceus with a maximum intensity of association occurring at Cape Arago, Oregon, and Clallum Bay and Manchester Dock, Washington. A survey of gonad smears and hematoxylin and eosin-stained sections indicated that the ciliate was only present in males. Spring-spawning E. troschelii and P. ochraceus are more negatively impacted by the ciliate than are winter-spawning Leptasterias spp. as judged by a skewed sex ratio and sex size differences, which may be associated with seasonal differences in water temperature affecting the growth rate of O. stellarum. The external morphology of O. stellarum appears to be similar throughout the geographical range surveyed.
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