Untitled

Abstract

SUMMARY: Lengths of cnidae, sampled from fresh tissue (tentacles, acontia or column) from the sea anemones Metridium senile (Linnaeus), Cereus pedunculatus (Pennant), Sagartia elegans (Dalyell), Sagartia troglodytes (Price), Anthopleura thallia (Gosse) and Urticina eques (Gosse), were measured. The mean, mode, median, standard deviation, variance, coefficient of variation, minimum, maximum and range of each sample were calculated. Lengths of nematocysts (basitrichs and microbasic p-mastigophores) and spirocysts had normal (Gaussian) frequency distributions, and there was no important within-sample variability. A between-sample (same specimen) difference was detected between mean lengths of microbasic p-mastigophores from acontia in Sagartia elegans. Intraspecific (between-specimen) differences amongst mean lengths of basitrichs from column ectoderm were detected amongst four specimens of Urticina eques, and a difference occurred between the mean lengths of microbasic p-mastigophores from the acontia of two specimens of Sagartia elegans. However, for each of the species U. eques and S. elegans, there was no direct 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 useful and a rapid sample range test is suggested for analysing differences between them. Methods are also presented for estimating means and standard deviations from data in publications that provide only ranges of cnida sizes and the number of cnidae measured. The present results and conclusions supplement those of Williams (1996, Scientia Marina, 60: 339-351).

Morphological revision of the genus Aiptasia and the family Aiptasiidae (Cnidaria, Actiniaria, Metridioidea)

“…We scanned through the slides and haphazardly chose 15 capsules of each type (when possible) to measure to generate a range: frequencies given are subjective impressions based on all the cnidae seen on the slides. For each type, a mean and standard deviation has been provided to give an idea of the distribution of sizes; these are not statistically significant (see Williams 1998Williams , 2000 for minimal requirements for statistical significance in cnida sizes) but provide some qualitative information about variability in capsule size for each type of nematocyst. Cnida terminology follows Mariscal (1974); however, we allude to Schmidt's (1969) terminology and correspondences between classifications because the latter is more detailed.…”

Cnidom in Ceriantharia (Cnidaria, Anthozoa): new findings in the composition and micrometric variations of cnidocysts

“…Regarding intra-structure variations, Williams (1996 , 1998 , 2000) analyzed the cnidocysts of five families of sea anemones and found that different samples of the same structure (mentioned as “tissue”) showed differences between the lengths of cnidocysts. Consequently, the mentioned author pointed out that, when sampling cnidocysts by using the classical approach followed to study the cnidom in sea anemones, the section of each structure should be clearly identified.…”