Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet of Parastichopus californicus (Echinodermata: Holothuroida).

The coelomic lining of the water-vascular canal in a suckered tube foot from the sea cucumber, Parastichopus californicus, is a pseudostratified myoepithelium consisting of flagellated adluminal cells and myofilament-bearing retractor cells. The bodies of adluminal cells flank the water-vascular canal and send basal processes between the underlying retractor cells to confront the podial connective tissue. Retractor cells have a contractile apparatus of unregistered thick and thin myofilaments. The contractile apparatus is confined to the medullary sarcoplasm and oriented parallel to the primary axis of a tube foot. The bodies and processes of retractor cells intermingle with the basal processes of adluminal cells at the basal lamina of the coelomic lining. A ganglionated nerve plexus in the podial connective tissue approximates the basal lamina. Neuronal connectives link the ganglia to one another and to the nerve plexus in deep sectors of the podial epidermis. External laminae enveloping the ganglia and connectives in the podial connective tissue are continuous with the basal lamina of the epidermis. The adventitial nerve plexus, since it merges with the epidermal nerve plexus, is a component of the ectoneural division of the echinoderm nervous system.