RECONSIDERING PREY SPECIALIZATIONS IN AN ALGAL-LIMPET GRAZING MUTUALISM - EPITHALLIAL CELL-DEVELOPMENT IN CLATHROMORPHUM-CIRCUMSCRIPTUM (RHODOPHYTA, CORALLINALES)

The association of the limper Tectura testudinalis (Muller 1776) and t he crustose coralline red alga Clathromorphum circumscriptum (Stromfel t) Foslie (Melobesioideae) is considered a species-specific mutualism between grazer and prey. Anatomical features of C. circumscriptum, esp ecially those associated with epithallial cells, have been viewed as b eing unusual and directly related to the mutualism. Transmission and s canning electron microscopic methods were used to investigate the stru cture and development of epithallial cells in C. circumscriptum. Contr ary to prior reports, terminal cells of the epithallial filaments of C . circumscriptum undergo senescence and shedding much like epithallial cells in other members of the Corallinales; hence, multicellular epit hallial filaments did not evolve in this alga simply because epithalli al cells were unable to slough. Although epithallial cells in many cor alline algae are lightly calcified, those in C. circumscriptum are hea vily mineralized, more so than the underlying initial cells and cells comprising the cortex. As in other coralline algae, starch is absent f rom the epithallial cells of C. circumscriptum. The feature of having abundant chloroplasts in the epithallial cells of C. circumscriptum is shared by other species with multicellular epithallial filaments and transiently by species with single epithallial cells. Except for havin g a thick epithallus, a feature found in other genera and in other spe cies of Clathromorphum, the anatomy of C. circumscriptum is unexceptio nal.