On the Biology of Gnathophylloides Mineri, a Shrimp Inhabiting the Sea Urchin Tripneustes Ventricosus

Abstract

ABSTRACT The small shrimp Gnathophylloides mineri is a common inhabitant of the short spines of the sea urchin Tripneustes ventricosus found in shallow waters of eastern St. Croix, United States Virgin Islands. It shows remarkable cryptic coloration and behavioral and morphological features suggesting a past history of intense predation pressure. Gnathophylloides mineri feeds on the epithelium covering the sea urchin spines which is abraded by toothed setae on the second maxillipeds and perhaps also by small, handlike structures on the dactyls of the walking legs. It seems likely that dark pigment from the host test is incorporated by the shrimp. Filter feeding also occurs. The shrimp are usually found in groups (up to 13 on a given host) with females greatly outnumbering males. Although there is a broad overlap in size distributions, males are significantly smaller. There is evidence that shrimp move between urchins. Differential male mortality during migration may explain the uneven sex ratio.