Ultrastructure of the tentacles of Themiste lageniformis (Sipuncula)

An ultrastructural study of the tentacles of T. lageniformis was conducted as part of a larger study of head metamorphosis in the species. The oral surface of the tentacles is constructed of a multiciliated, pseudostratified, columnar epithelium while the aboral surface is an unciliated, cuboidal epithelium. Intraepidermal mucous cells lie near the junction of the oral and aboral regions. The basal portion of the epidermal cells is embedded in a thick, collagenous extracellular matrix which contains outer circular muscles, inner longitudinal muscles, the main tentacular nerve and its branches. Justification for the designation of the tentacular canals as coelomic rather than vascular is discussed.