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Cnidae variability in the polyp tentacles of the Scleractinian corals Cladocora caespitosa (Linnaeus, 1767) and Balanophyllia europaea (Risso, 1826) in the Adriatic Sea

Cnidae, products of intracellular secretion diagnostic of the phylum Cnidaria, have acquired various degrees of importance in cnidarian groups, but were rarely used as taxonomic characters. Traditionally, skeleton structure has been the main source of taxonomic characters for scleractinian systematics, whereas information from soft tissues has been comparatively neglected. The use of soft tissue characters (e.g. polyp anatomy, cnidae size) is routine in the study of other soft haxacoralian orders. The cnidae composition from the polyp tentacles of two species - Cladocora caespitosa (Linnaeus, 1767) and Balanophyllia europaea (Risso, 1826) have been studied from 5 stations in the Adriatic Sea. Living specimens of each species were used ; the length of at least 50 unfired capsules from the tentacles were measured and taken from the following categories: spirocyst, basitrich2, basitrich3, holotrich2 and microbasic p-mastigophore. A total of 2.500 measurements were done. The data were analyzed with descriptive statistics (mean, standard deviation, median, maximum and minimum by Box-Whiskers plot), Bray-Curtis index and Model II ANOVA. Most of the cnidae common to both species showed slight differences in average and size range. As a general rule, the average and size range reached higher values in B. europaea, than in C. caespitosa. The data obtained have show consistent qualitative and quantitative differences between the two species. This study shows that the cnidae characters can be useful taxonomic criteria for distinguishing scleractinian species.

Cnidae variability; Cladocora caespitosa; Balanophyllia europaea; Adriatic Sea

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