The early evolutionary history of echinoderms was reconstructed on the basis of structural-functional considerations and application of the quasi-engineering approach of ‘Konstruktions-Morphologie’. According to the presented evolutionary scenario, a bilaterally symmetrical ancestor, such as an enteropneust-like organism, became gradually modified into a pentaradial echinoderm by passing through an intermediate pterobranch-like stage. The arms of a pentaradial echinoderm are identified as hydraulic outgrowths from the central coelomic cavity of the bilateral ancestor which developed due to a shortening of the body in (...) length but widening in the diameter. The resulting pentaradial symmetry is a consequence of mechanical laws that dictate minimal contact surface areas among hydraulic pneumatic entities. These developed in the coelomic cavity (metacoel) in the bilaterally symmetrical ancestor, when from the already U-shaped mesentery with the intestinal tract two additional U-shaped bows developed directly or subsequently. During the subsequent development tensile chords of the mesentery ‘sewed’ the gut with the body wall first in three and secondly in five ‘seams’. During the direct development five ‘seams’ between tensile chords and body wall developed straightly. These internal tensile chords subdivide the body coelom into five hydraulic subsystems (‘pneus’), which eventually arrange in a pentaradial pattern. The body could then enlarge only between the tensile chords, which means that five hydraulic bulges developed. These bulges initially supported the tentacles and finally each of them enclosed the tentacle until only the feather-like appendages of the tentacles projected over the surface. The tentacles with their feathers were transformedinto the ambulacral system, and the bulges become the arms. These morphological transformations were accompanied and partly determined by specific histological modifications, such as the development of mutable connective tissues and skeletal elements that fused to ossicles and provided shape stabilization in form of a calcareous skeleton in the body wall. The organism resulted was an ancestral echinoderm (‘Ur-Echinoderm’) with an enlarged metacoel, stabilized by hydraulic pressure working againsta capsule of mutable connective tissue, skeletal elements and longitudinal muscles. In regard to these reconstructions, the body structure of echinoderms can be understood as a hydraulic skeletal capsule. (shrink)

A method of phylogenetic reconstruction as proposed by a number of scientists of the Senckenberg Research Institute is discussed. The method is based on functional-morphological studies, the evolutionary adaptation principle of Bock and Von Wahlert (1965) and so-called model reconstruction. It is argued in this paper that direction of the adaptation process cannot be determined because of lack of knowledge about particular selective forces and that theories of model reconstruction are not open to contradiction in the sense of Popperian falsification. (...) Although it has been claimed that the method provides the only valid directional argument for morphoclines in cladistic studies, it remains unclear how to proceed when morphoclines show contradictory polarities. Moreover, it is doubtful whether polarities of morphoclines can be determined independently of phylogenetic hypotheses, and also whether the use of multistate morphoclines is methodologically valid. By relying on a particular evolutionary theory, i.e. the neo-Darwinian theory, and consequently assigning natural selection as the major agent of directional progress, the Senckenburg method of phylogenetic reconstruction restricts itself to microevolutionary change and, therefore, cannot be used when other hypotheses on the evolutionary process appear to explain the speciation process more plausibly, i.e. hypotheses on macroevolution. Furthermore, it is an unproved statement that evolution always proceeds according to the principle of economy. (shrink)