A light and electron microscopic study of the ciliated urn of Phascolosoma agassizii (sipunculida)

Summary The free swimming ciliated urn found in the coelomic fluid of Phascolosoma agassizii has been studied by electron microscopy. The urn is a multicellular structure composed of three cell types: (a) ciliated cells which possibly function in capturing cell debris and foreign particles; (b) cupola cells which are capable of phagocytozing latex particles; and (c) lobe cells which are capable of phagocytozing carbon particles. The lobes are separated from the ciliated cells by a semilunar area, with mucoprotein staining characteristics, containing fibrils which appear to be the structural support for the urn. Ciliated cells and lobes are attached to the semilunar area by hemidesmosomes.This work is based on a thesis submitted in partial fulfillment of the requirements for the degree Master of Arts in the Department of Biology, San Francisco State University, San Francisco, California, U.S.A.I wish to thank Dr. John C. Lee, formerly of the Department of Pathology, University of California Medical Center, San Francisco, for encouragement and use of his electron microscope facilities     

Über den Aufbau des Integumentes der Priapuliden und der Sipunculiden [Priapulus caudatus Lamarck,Phascolion strombi (Montagu)]

Zusammenfassung Die Epidermis von Priapulus caudatus besteht aus E. R.-reichen Zellen, deren chromatinarme Kerne apikal von zahlreichen Mitochondrien umgeben werden. Distal lagert eine dicke Kutikula, die aus feinfaserigem Material besteht. Die basale Plasmamembran ist zu einem umfangreichen Labyrinth aufgefaltet.Die Epidermis von Phascolion strombi weist nur wenig endoplasmatisches Retikulum auf. In den Zellen kommen viele Tonofilamentbündel vor. Das basale Plasmalemm ist aufgefaltet. Die Kutikula besteht aus vielen Schichten rechtwinklig gegeneinander versetzter Fibrillenlagen. Dieser ultrastrukturelle Bau einer Kutikula tritt sonst nur bei den Anneliden auf. Im Bereich der Tentakel findet sich keine Kutikula. Das Epithel ist hier mit einem Mikrovillussaum versehen und trägt an manchen Stellen Zilien.

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The fine structure of the integument of priapulids and sipunculids (Priapulus caudatus, Phascolion strombi)

Summary The epidermis of Priapulus caudatus consists of cells with strikingly pale nuclei and an abundant granular endoplasmic reticulum. The apical parts of the nuclei are surrounded by dense clusters of mitochondria. The thick cuticle consists of fibrous material. The basal plasmalemma exhibits up-foldings that build up a labyrinthine system of intercellular spaces.The epidermis of Phascolion strombi which is poor in endoplasmic reticulum, is characterized by many bundles of tonofilaments. The basal plasmalemma exhibits simple up-foldings. The cuticle consists of layers of fibrils, which are orientated at right angles over each other. A similar cuticle has been found in the class of Annelids. In the area of the tentacles there is no cuticle, the epithelium bears microvilli and cilia.

Herrn Prof. Dr. W. Bargmann und Herrn Prof. Dr. O. Moritz danken wir für die Überlassung eines Arbeitsplatzes im Anatomischen Institut und im Institut für Pharmakognosie Kiel.     

Epidermal ciliary ultrastructure of adult and larval sipunculids (Sipunculida)

The ultrastructure of the ciliary apparatus of multiciliated epidermal cells in larval and adult sipunculids is described and the phylogenetic implications discussed. The pelagosphera of Apionsoma misakianum has a dense cover of epidermal cilia on the head region. The cilia have a long, narrow distal part and two long ciliary rootlets, one rostrally and one vertically orientated. The adult Phascolion strombus has cilia on the nuchal organ and on the oral side of the tentacles. These cilia have a narrow distal part as in the A. misakianum larva, but the ciliary rootlets have a different structure. The first rootlet on the anterior face of the basal body is very short and small. The second, vertically orientated rootlet is long and relatively thick. The two ciliary rootlets present in the larval A. misakianum are similar to the basal metazoan type of ciliary apparatus of epidermal multiciliated cells and thus likely represent the plesiomorphic state. The minute first rootlet in the adult P. strombus is viewed as a consequence of a secondary reduction. No possible synapomorphic character with the phylogenetically troublesome Xenoturbella was found.