Description of the larval stages of Tisbe cucumariae (Copepoda: Harpacticoida) and comparative development within the genus Tisbe

For T. cucumariae Humes setation and segmentation are described for all 6 naupliar and all 5 copepodid larval stages. This sequence of anatomical development is expressed numerically and compared with development sequences previously described for 4 other species of Tisbe: (T. longisetosa, T. gracilis, T. reticulata and T. furcata ). Interspecifically, the nauplii are more dissimilar than the subsequent copepodids. This is a violation of the general rule that among animals developmental stages become progressively more diverse (von Baer's third law). One possible explanation for this violation is cenogenesis. A second possibility is that the earlier the developmental stage, the smaller its size, and the greater becomes the chance of inaccurate description.