Structure of a solitary and a colonial species of Stephanoscyphus (scyphozoa, Coronatae) with observations on periderm repair

Abstract

1. A solitary and a branched (colonial) species of Stephanoscyphus belonging to the scyphozoan order Coronatae were studied by means of histochemistry, light microscopy and by transmission and scanning electron microscopy. 2. Coronate polyps are unlike all other cnidarian polyps in having a ring sinus in the oral end with four per-radial openings to the coelenteron. 3. The lining of the lateral wall of the ring sinus is remarkable in that the cells are so large, most of the cytoplasm is taken up by a large vacuole, the nucleus is apical and between some of the cells are unbranched elastic fibers aligned at right angles to the epithelial surface. 4. The organization of the muscular system is also peculiar because much of it is related to the ring sinus. Musculo-epithelia from the oral disk and medial sinus wall meet and continue aborally as four flattened tubular retractors containing cnidoblasts. 5. In the colonial species some muscle fibers contain structures resembling ciliary rootlets. 6. The intermediate layer is of the mesolamella type. 7. The tentacles have longitudinal ectodermal epithelio-muscular cells and a solid core composed of a single line of vacuolated endodermal cells which contain peripheral fibrous rings. 8. The medial sinus wall and the epithelia of the calyx can be less than 0.1 μm. 9. The ectoderm and endoderm of the calyx-stalk are each composed of one cell type. This is the simplest organization for the body wall of any cnidarian polyp. 10. There are four small septa in the oral region. 11. Four special cellular bands, called filaments, are found in the coelenteron starting in the oral disk then travelling along the edge of the septa finally going aborally along the stalk. In the oral region the filament is round in cross-section then flattens out aborally. 12. The neurites are typically cnidarian (neurotubules, granular vesicles but no Schwann cells) and were noted in the filaments and retractor muscle tubes but the tentacles lacked neurites. 13. Teeth are formed only after 4 μm of the periderm are laid down. Next the soft-body invaginates at the tooth site and then the ectoderm secretes the tooth periderm. 14. The tubal periderm thickens at 0.6 μm per day and stops when it reaches about 20 μm. 15. An experimental hole in the periderm is not filled in but the bottom is covered over by new periderm which would have been secreted anyway in an intact polyp. The ectoderm over the hole thickens but histochemistry failed to show anything definite. 16. The periderm can be divided into two layers: the 4 μm outer sulptured layer is formed by a special thick band of ectoderm at the oral end of the calyx; the thicker part of the periderm is smooth and is formed by the ectoderm of the calyx and stalk. 17. The cytological peculiarities, comparative anatomy and functional morphology are discussed. © 1972 Biologischen Anstalt Helgoland.