Cuticular pores and spines in the Pedicellinidae and Barentsiidae (Entoprocta), their relationship, ultrastructure, and suggested function, and their phylogenetic evidence

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Abstract
The cuticular pores and hollow spines often described as species-characteristic integumental differentiations in numerous Entoprocta, mainly in the Pedicellinidae and Barentsiidae, are shown to be comparable and, by intermediate stages, linked structures, the development of which is governed by environmental conditions. Because of their great variability they are of lesser value for the species characterization than hitherto assumed. Clusters of specialized epithelial cells underneath the cuticular openings or spine channels are investigated by means of electron microscopical and cytochemical methods, and are interpreted as ion-regulatory organs (“chloride cells”) being homologous with the protonephridia one can observe in a similar position in the fresh-water entoproct Urnatella.