Measurements of cnidae from sea anemones (Cnidaria: Actiniaria), III: ranges and other measures of statistical dispersion, their interrelations and taxonomic relevance

Abstract

SUMMARY: This is the third of a series of papers examining the taxonomic relevance of some statistical treatments of measurements of cnidae from sea anemones (Actiniaria). Some cnida lengths from fresh tissue samples (column ectoderm, tentacles or acontia) from Nematostella vectensis, Haliplanella lineata, Sagartia elegans, Metridium senile, Cereus pedunculatus, Sagartia troglodytes, Anthopleura thallia, Urticina eques and Sagartiogeton laceratus were measured. Five measures of statistical dispersion (sample standard deviation, coefficient of variation, observed sample range, standard range, and 99% probable maximum value of the standard range) were calculated, and their interrelations and potential applications were appraised. It has long been the convention to use the largest and smallest cnida sizes (observed sample range) from tissue samples in attempts to establish differences between actiniarian taxa. However, such data do not reflect the true extremes of a population range. In the present study, the 99% probable maximum value of the standard range for a standard abundance of 1,000 gave the greatest and, therefore, the most cautious estimate of a population range of cnida sizes for a species. This maximum standard range is the only measure of dispersion of cnida sizes that may be used validly to demonstrate that anemone specimens are of different species, and then only if there is no overlap between the extreme cnida sizes being compared. However, partial or complete overlaps of cnida size extremes do not necessarily indicate that specimens are conspecific; other taxonomic characters must also be considered. Coefficients of variation may provide valuable clues as to the homogeneity or heterogeneity of samples of cnida measurements. This paper should be read in conjunction with the first two in this series, which address the taxonomic relevance of differences between mean cnida sizes

Biometric and statistical investigations on the cnidoma of the genus Hydra (Cnidaria, Hydrozoa)

“…Many authors have studied quantitative aspects of nematocysts belonging to different cnidarian taxa (Weill, 1934;Mariscal, 1974;ÖstMan et al, 1987;thoMason, 1989;chintiroglou et al, 1996;Panagiotis & chintiroglou, 1997;WilliaMs, 1998;acuña et al, 2003;Fautin, 2009), and most of them have applied traditional statistical tools, such as parametric and nonparametric tests.…”

“…Since carlgren (1900) the description of nematocysts has drawn attention of many researchers for a long time. An inventory of all the cnidae types present in the tissues of a cnidarian is known as its cnidoma (Weill, 1926) but no information on cnidae size is implicit in this definition (WilliaMs, 1998).…”

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

“…This premise is essential for admitting the cnidome as a valid taxonomic character in scleractinians, but it should take into account intraspecific variability that may be expressed at geographical, ontogenetic or ecological levels (e.g. Williams, 1998), as well as the spatial distribution of the cnidae in different parts of the polyp, since this may not be homogeneous (Ardelean, 2003). Qualitative differences at a generic level in scleractinian were already observed by Pires and Pitombo (1992) Brazilian Mussidae (four species, three of them congeneric).…”

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“…They serve a variety of purposes in the lives of cnidarians and comprise three main types: nematocysts, spirocysts and ptychocysts (Williams, 1996). Nematocysts are further subdivided into about 25 types (Mariscal, 1974).…”