Responses of solitary and colonial coronate polyps (Cnidaria, Scyphozoa, Coronatae) to sedimentation and burial

Coronate polyps retract their soft bodies into a protective peridermal tube after mechanical irritation. Sediment may enter the tube of contracted polyps, however, and block the opening [Jarms, G., 1990. Neubeschreibung dreier Arten der Gattung Nausithoe (Coronatae, Scyphozoa) sowie Wiederbeschreibung der Art Nausithoe marginata Kölliker, 1853. Mitt. Hamb. Zool. Mus. Inst. 87, 7-39; Silveira, F.L. da, Jarms, G., Morandini, A.C., 2003. Experiments in nature and laboratory observations with Nausithoe aurea (Scyphozoa: Coronatae) support the concept of perennation by tissue saving and confirm dormancy. Biota Neotropica 2 (2), 1-25]. In the present study, the ability of different coronate species [Nausithoe aurea Silveira and Morandini, 1997, Nausithoe planulophora (Werner, 1971), Thecoscyphus zibrowii Werner, 1984, Linuche unguiculata (Swarts, 1788)] to expel sediment particles from the tube was investigated. In laboratory experiments, sand grains and mussel shell fragments were inserted into the tubes and the responses of polyps were observed. Particles were ingested as polyps extended themselves, and after extension, they were defecated. Ingestion was effected by an aborally directed flagellar beat of the flagellated gastrodermal epithelia that was reversed for defecation. Particles only slightly smaller than the tube opening could be expelled, and extension of the polyp was possible even if grains blocked 2/3 of the tube. However, if particles became stuck in the tube, ingestion was impossible and polyp extension failed. Comparisons among the tested species showed that expulsion success depended on tube shape and polyp morphology. In N. aurea and N. planulophora, less than 5% of tubes were permanently blocked. The cave-dwelling species T. zibrowii was not able to ingest particles due to its particular morphology, and in 25% of experiments with shell fragments tubes were permanently blocked. Thin, elongate tubes of the colonial polyps L. unguiculata were also often permanently blocked by shell fragments (50%), but new polyps were developed from the scyphorhiza to ensure survival of the colony. Solitary polyps were able to survive more than 5 months retracted beneath any blocking particles. After tubes were cut off beneath such particles normal polyps developed. From our observations, we suggest that coronate polyps can exist in habitats with moderate sedimentation, and that they can survive being temporarily buried.