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Epizoanthus is a poorly known zoantharian genus in need of further study. Benthic surveys have shown that E. papillosus (until recently considered rare) is quite abundant in the Celtic Sea, Minches and northern North Sea, occurring as carcin-oecia formed in association with Anapagurus laevis (Anomura, Paguridae) and as smaller free-living colonies. It is also extensively distributed in the western Atlantic. A study of the cnidom in tentacles and mesenteric filaments has shown that carcinoecia contained fewer types and smaller numbers of nematocysts (basitrichs, p-mastigophores, and two different holotrich types) and spirocysts than free-living colonies, probably a consequence of being able to scavenge food from the pagurid. A method for obtaining quantitative estimates of spirocyst abundance is described. The mesenteric filaments of two of the three carcinoecia analysed contained numerous unexploded nematocysts (kleptocnidae) sequestered from the scyphomedusan Cyanea (probably C. capillata), presumably derived from the long tentacles trailing over the sea bed. This occurrence has never previously been recorded. The taxonomic study of larger, deep-sea, carcinoecium-forming species of Epizoanthus is complicated by the same paucity of nematocysts noted for E. papillosus.

Colonial zoanthids are a conspicuous feature of the subtropical rocky intertidal in KwaZulu-Natal but those of the genus Zoanthus have a confused taxonomy with 10, difficult to separate, nominal species described from the region. This paper presents an analysis of polyp size, measured as mean diameter determined photographically from the number of polyps occupying an area of 6 × 4 cm(2). The results, based on diameter frequency of 127 samples from five shores, indicate three populations (morphotypes) with means of 4.3 (SD ±0.53), 5.7 (SD ±0.70) and 8.4 (SD ±0.58) mm occurring in the approximate abundance ratios of 10:5:1, possibly corresponding to Zoanthus sansibaricus, Z. natalensis and Z. lawrencei. The underlying assumptions with regard to population structure (the number, size and degree of fragmentation of clones) and the normality of data are discussed, as are trans-oceanic larval dispersal, recruitment, and genetic connectivity. The essential, traditional species description in Zoanthus, using internal morphology, on its own may be an inadequate discriminator of species. The status of the few possibly valid species is discussed in relation to the present results and recent studies based on the application of molecular genetics. Thorough studies of the population structure (genets and ramets) and a taxonomic approach based on the combined use of morphology, genetic methods and statistically robust, quantitative morphometrics are proposed as a potential way forward.

Cnidae have been used in hexacoral taxonomy since 1900 but their value at species-level remains controversial. Data given in descriptions have generally been cnida types, their distribution, and capsule sizes presented as ranges (maxima and minima). More recently, measurements of cnida capsules, treated as populations, have been employed. Sampling cnidae extracted from zooids ranging from buds to full-grown polyps, we have analysed 28 300 random measurements of capsule length and width in 133 samples taken from two colonies of the zoanthid Acrozoanthus australiae , one from Queensland, Australia, and one from Indonesia. Using image analysis we measured large holotrichs, microbasic b -mastigophores and p -mastigophores, basitrichs being absent. Length has a lower coefficient of variation than width. Up to 12% of sample distributions were non-normal, depending on the test employed, but there was no consistent pattern of departure from normality. Sample sizes of 50 are regarded as adequate for the calculation of means and variances but need to be larger (contrary to current practice) for an accurate estimation of range. Moreover, some ranges were asymmetrical with respect to the sample mean. Statistical methods for comparing ranges are lacking, so sample size, mean and a measure of variance must always be included. Capsule sizes often differed significantly along the length of tentacles and filaments; they also showed significant differences between polyps within a colony, sometimes clearly correlated with polyp size. It is suggested (based on size frequency distributions that are right skewed or bimodal) that new buds may contain residual cnidae derived from the parent polyp as well as others that have differentiated in situ . Though length appears to be the most useful capsule descriptor, bivariate (width: length) scattergrams provide a concise summary of capsule size, also displaying cnida type and source. We make several recommendations for future practice. [ABSTRACT FROM AUTHOR]