The origin and homology of the jointed appendages of carpoid and pelmatozoan echinoderms
The study of the origin and homology of the jointed appendages used for feeding, attachment and motion in the Pelmatozoa (Crinozoa and Blastozoa) and the Carpozoa (Soluta, Cincta, and Stylophora) is primarily based on reconstructions of the ontogeny of these animals. The presence or absence of some key processes occurring in the ontogeny of recent crinoids can be revealed in the early Paleozoic pelmatozoan and carpoid echinoderms by analyzing their adult and aberrant morphologies. Similarities in the morphology of crinoid arms, blastozoan brachioles and the feeding appendage of solutes can be explained by a similar growth pattern, based on the initial organizing role of the radial ambulacral canal. This growth model can be referred to as the model of apical serial enantiomorphic monopodial branching (ASEM-branching model). Differences between crinoid arms and blastozoan brachioles derive from the initiation of the crinoid arms anlagen in the closed vestibular sac. The solute feeding appendage is actually a pharyngeal extension. The hydrocoel was sac-like and did not grow around the pharynx in the solute ontogeny while torsion was present. The homoiostele of solutes is a homologue of the crinoid and blastozoan stem because it originated from the larval preoral lobe and right somatocoel. Cincta underwent torsion during development. The homology of cinctan marginals to those of Ctenoimbricata, Courtessolea, and the Ctenocystoidea is unlikely because these groups have very different internal body plans. Stylophorans lacked torsion and the aulacophore originated from the preoral lobe and food groove similar with the endostyle of tunicates and lanceletes. Most probably, the aulacophore was lacking of longitudinal (radial) canal. How to cite this article: Rozhnov S.V. 2017. The origin and homology of the jointed appendages of carpoid and pelmatozoan echinoderms // Invert. Zool. Vol.14. No.2. P. 174-181. doi: 10.15298/invertzool.14.2.12