ABSTRACT
The tube feet of 30 species of comatulid crinoid were examined using electron and light microscopy. The adhesive structures of the tube feet are located in papillae. Papillae consist of a microtubule cell (unique to crinoids); uniciliated nerve cells with secretions similar to those found in Type 2 cells; three types of secretory cell (A, B and C) and support cells. Secretory cells are all of the goblet type. Type B cells contain a flocculent “mucus” and are found elsewhere in the tube foot, in the lappets and in the ciliated food-groove. Type A and C cells have heterogeneous secretions and occur only in the papillae. Three different models of papillar adhesive processes are described and discussed. The morphological evidence supports the hypothesis that crinoid diverged from the other four classes early in the evolution of the modern classes and that the echinoids and holothurians form a distinct evolutionary line.
