The morphology of the digestive tract and respiratory organs of the holothurian Cladolabes schmeltzii (Holothuroidea, Dendrochirotida)

Abstract

The microanatomy of the digestive and respiratory systems of the holothurian Cladolabes schmeltzii was studied. The digestive tube of C. schmeltzii is divided into seven parts. The pharynx, esophagus, and stomach are lined with cuticular immersed epithelium. In these regions, the epithelial cells are connected via desmosomes, septate junctions, and rivet-like structures. The presence of the cuticle and rivet-like structures suggests an ectodermal origin for these parts of the digestive tube. The luminal intestinal epithelium is formed by vesicular enterocytes, which have different structures in different intestinal regions. Moreover, the epithelium of the first descending part of the intestine contains the granular enterocytes. The respiratory system consists of paired respiratory trees lined by a luminal epithelium that is formed by cells of irregular shape. The apical surface of these epithelial cells has few lamellae. The cells are connected to each other through a system of intercellular junctions, consisting of both desmosomes and well-developed septate junctions. The coelomic epithelium of the intestine and the respiratory trees consists of peritoneal and myoepithelial cells.