Ultrastructure of transrectal coelomoducts in the sea cucumber Parastichopus californicus (Echinodermata, Holothuroida)
The perivisceral coelom of the sea cucumber Parastichopus californicus is connected to the lumen of the hindgut by as many as 200 short transrectal ducts. Each duct is lined by a pseudostratified epithelium composed of: (i) monociliated, tonofilament-containing cells, (ii) myoepithelial cells, (iii) bundles of neurites, and (iv) granule-containing cells. In most places the lumen of each duct is lined by the monociliated, tonofilament-containing cells. The myoepithelial cells are predominantly basal in position and circular in orientation, but some border the lumen and parallel the long axis of the duct. The epithelium of a duct consists of the same types of cells as occur in the peritoneum covering the rectum and differs markedly from the nonciliated, cuticularized epithelium that lines the lumen of the rectum. Based on ultrastructural characteristics, the transrectal ducts represent evaginations of the peritoneum overlying the rectum and are thus "coelomoducts" sensu Goodrich. The possibility is discussed that perivisceral coelomoducts of holothuroids function in regulating coelomic volumes.
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George L. Shinn, Stephen A. Stricker, and Michael J. Cavey "Ultrastructure of transrectal coelomoducts in the sea cucumber Parastichopus californicus (Echinodermata, Holothuroida)" Zoomorphology (1990) 109 : 189-199