Cnidae variability in Balanophyllia europaea and B. regia (Scleractinia: Dendrophylliidae) in the NE Atlantic and Mediterranean Sea

Traditionally and for practical reasons, skeleton structure has been the main source of taxonomic characters for scleractinian systematics, whereas information from soft tissues has been comparatively neglected. However, skeleton variability may leave species identification uncertain. The use of characters from soft tissues (e.g. polyp anatomy, cnidae size) is routine in the study of other (“soft”) hexacorallian orders. This contribution aims to determine whether cnidae characters are useful in taxonomic studies of scleractinians. The cnidae composition of two congeneric species—Balanophyllia europaea (Risso, 1826) and Balanophyllia regia Gosse, 1860 have been studied throughout a wide geographical area. The data obtained show consistent qualitative and quantitative differences between the two species. This study shows that the cnidae characters can be useful taxonomic criteria for distinguishing congeneric species