Geometric morphometric and biometric analysis for the systematic elucidation of Brachionus caudatus Barrois and Daday, 1894 (Rotifera Monogononta Brachionidae) forms

Taxonomy of the genus Brachionus (Brachionidae) poses problems common to many members of Rotifera. Like other genera, Brachionus includes species showing a remarkable phenotypic plasticity. Biometric and geometric morphometric analyses were applied to re-evaluate the taxonomic status of two of its morphological forms, Brachionus caudatus “f”. ahlstromi and Brachionus caudatus “f”. austrogenitus using specimens collected in different aquatic environments of the floodplain of the Paraná River. The biometric analysis was based on the measurement of the anterior width, maximum width and body length. Fourteen landmarks were considered for the geometric morphometric analysis. The biometric analysis (using the t-test) revealed significant differences ( p < 0.0001 ) in the dimensions of all three variables. Multivariate analysis of variance (MANOVA) of geometric morphometric data also showed that these morphs were significantly different ( p < 0.0001 ). These results provide substantial evidence to consider both morphs as separate taxonomic entities.