ABSTRACT
By constructional morphological argumentation the mechanical and architectural prerequisites of the holothurian body construction (defined in general terms of physical apparatuses) are explained. Thus, the evolutionary development of the body form and of several auxiliary parts can be reasonably reconstructed.
Pharyngeal rings of Devonian holothurians seem to confirm the deduction that parallel with the evolutionary elongation of the body, biserial rows of ambulacrals altered into pseudo-perradial (uniserial) rows of high elements. The first element of each row, the holothurian radiais, apparently have the Lovenian configuration inherited from complete ambulacral fields of a phylogenetic forerunner.
