Effects of nonnormality on studies of morphological variation of a Rhabdomesine bryozoan, Streblotrypa (Streblascopora) prisca (Gabb and Horn)

Abstract

Abstmet.-Documentation of morphological variability associated with spatial distribution (i.e., geography) is important for microevolutionary studies. In a study of geographical variation, the morphological variability of forty-six specimens (colony fragments)of Streblohypa was documented from eight localities of the Winzeler Shale (Stephanian, Midcontinent, USA), along a 300-km-long transect. Multivariate analysis of 28 morphometric characters demonstrated the presence of a single species of Streblotrypa in the study material.Evaluation of this large, morphometric data set demonstrated that a sample size of 5 observations per colony fragment is optimal for this type of study and that effects of violating assumptions of normality and ltomoscedasticity are present but do not affect overall conclusions with these data. Consequences of violating these assumptions are important, however, when strict probability cut-offs are employed.Streblotopa ulrichi and S. striatopara are recognized as astogenetic variants and designated as junior synonyms of S. (Streblascopora) prism. The spelling of the type species of the genus is corrected to Streblohypa nicklesi, and a neotype is designated.