ABSTRACT
Functional morphology of the clavules in the spatangoid echinoid Echinocardium cordatum (Echinodermata). Echinocardium cordatum harbors particular miliary spines (i.e., clavules) that organize in tracks called fascioles. Clavules are densely packed (ca. 120/mm2) and measure from 0.8 to 2.5 mm in length depending on the fasciole. Each clavule is made of a short glandular head supported by a rather elongated vibratile stem. Clavules of the anal and subanal fascioles and most clavules of the inner fasciole (except those surrounding the apical tuft) secrete mucopolysaccharidic substances; these are used to trap and convey detrital particles along the anterior food groove (inner fasciole) or to trap fecal material (anal and subanal fascioles). Clavules of the part of the inner fasciole that surrounds the apical tuft secrete a mixture of polysaccharides and proteins; these are incorporated into the wall of the echinoid burrow -including the chimney- forming a kind of cement that reinforces the burrow’s wall and allows to keep an area free of sediment around the echinoid.
