The digestive tract of the echinopluteus of Echinocardium cordatum (Echinodermata, Echinoida): its ultrastructure and innervation

The digestive tract of the echinopluteus of Echinocardium cordatum consists of a tubular oesophagus, spherical stomach, and large hemispherical intestine. The oesophagus is constructed from cells of one ultrastructural type and has subepithelial muscles oriented circumferentially and longitudinally. The cardiac and pyloric sphincters separating the stomach from the oesophagus and intestine, as well as the anal sphincter, consist of myoepithelial cells and subepithelial muscles. The cells of both the stomach and intestine are able to absorb nutrients and phagocytize food. Neuron-like cells were detected around the mouth, in the oesophageal epithelium, and around the anal opening. Axonal trunks pass at the base of the oesophageal epithelium and around the sphincters. The rest of the digestive tract is innervated by solitary axons. Catecholamine-containing neurons were found inside the lower lip ganglion, in the two suboral ganglia, and around the anal opening.