MEASUREMENTS OF CNIDAE FROM SEA-ANEMONES (CNIDARIA, ACTINIARIA), II -FURTHER-STUDIES OF DIFFERENCES AMONGST SAMPLE MEANS AND THEIR TAXONOMIC RELEVANCE

Lengths of cnidae, sampled from fresh tissue (tentacles, acontia or co lumn) from the sea anemones Metridium senile (Linnaeus), Cereus pedunc ulatus (Pennant), Sagartia elegans (Dalyell), Sagartia troglodytes (Pr ice), Anthopleura thallia (Gosse) and Urticina eques (Gosse), were mea sured. The mean, mode, median, standard deviation, variance, coefficie nt of variation, minimum, maximum and range of each sample were calcul ated. Lengths of nematocysts (basitrichs and microbasic p-mastigophore s) and spirocysts had normal (Gaussian) frequency distributions, and t here was no important within-sample variability. A between-sample (sam e specimen) difference was detected between mean lengths of microbasic p-mastigophores from acontia in Sagar-tia elegans. Intraspecific (bet ween-specimen) differences amongst mean lengths of basitrichs from col umn ectoderm were detected amongst four specimens of Urticina eques, a nd a difference occurred between the mean lengths of microbasic p-mast igophores from the acontia of two specimens of Sagartia elegans. Howev er, for each of the species U. eques and S. elegans, there was no dire ct correlation between the sizes of the anemones examined and the mean lengths of their nematocysts. Overall, the results confirm that cnida size, when taken in isolation, is not a reliable taxonomic character for sea anemones. For other purposes? mean cnida measurements may be u seful and a rapid sample range test is suggested for analysing differe nces between them. Methods are also presented for estimating means and standard deviations from data in publications that provide only range s of cnida sizes and the number of cnidae measured. The present result s and conclusions supplement those of Williams (1996, Scientia Marina, 60. 339-351).