NEMATOCYSTS IN TUBULARIA LARYNX (CNIDARIA, HYDROZOA) FROM SCANDINAVIAAND THE NORTHERN COAST OF SPAIN

The morphology, distribution and function of nematocysts of Tubularia larynx Ellis and Solander 1786 (Ectopleura larynx sensu Petersen 1990) from Scandinavia and from the northern coast of Spain were studied by light and scanning electron microscopy, Differences were found betwee n the cnidomes of the two populations. The nominal species T. larynx m ight prove to comprise more than one species, one from Scandinavian wa ters and the other from northern Spain. Four categories of nematocysts were identified in the Scandinavian T. larynx and five categories in the Spanish T. larynx. Morphologically identical nematocysts were foun d within the categories of stenoteles, desmonemes, microbasic mastigop hores and isorhizas in the two hydroid populations. The fifth category , the euryteles, was however only identified in the Spanish hydroids. The size of the stenoteles and differences in the nematocyst distribut ion were additional features separating the two hydroid populations. P rey-capturing experiments were performed with Artemia sp. nauplii, mar ine plankton and small invertebrates living close to or in the Tubular ia colonies, Artemia naupulii were captured, paralysed and eaten. Most small planktonic crustaceans were also preyed upon, but Evadne sp., P odon sp. and large planktonic copepods often escaped. Other crustacean s, for example Corophium sp., members of the families Harpacticidae, C aprellidae and Ieridae, which lived in the Tubularia colonies were nei ther paralysed nor captured.