SKELETAL MORPHOLOGY OF 2 CONTROVERSIAL POECILOSCLERID GENERA (PORIFERA, DEMOSPONGIAE) - DISCORHABDELLA AND CRAMBE

The genera Discorhabdella and Crambe are characterized by bearing unco mmon spicule types, i.e. pseudoastrose acanthostyles and sphaeroclones , respectively. They have traditionally been considered to be unrelate d taxa, but the present reexamination made evident that an important a mount of skeletal features are shared by both. Some of these morpholog ical features, such as the ornamentation on the point of the ectosomal subtylostyles, are reported for the first time. The study also reveal ed that a tuberose nature of the tyles of the main choanosomal megascl eres could be a common ancestral condition in both genera. The morphol ogy of the multi-toothed anchorate chelae showed a gradual transition across the species, suggesting that the morphological diversity in che lae was generated in these genera through a ''palmate-anchorate-arcuat e'' evolutionary sequence. However, the forward or backward direction of this sequence remained unclear from the available evidence. Importa nt levels of skeletal variability were found to affect many of the ske letal characters, especially in the genus Crambe. In some cases, this variability transgressed the Limits theoretically defining a species, making evident that the traditional procedure just based on comparison of the skeletons becomes unreliable when tackling the taxonomy of the se genera. Most of the skeletal variability seemed to correspond to ge netic polymorphisms, except in the case of C. acuata. In this taxon, t he skeletal variability could be a result of the existence of a crypti c species, originated by a misconceived synonymy between C. acuata and C. chelastra. Besides the skeletal variability, the obscure taxonomic meaning of many skeletal features favored the existence of conflictin g taxonomic proposals for the suprageneric location of these genera, d epending on the author's criteria. This study made evident that any su bsequent attempt of phylogenetic inference should be based on an unwei ghted analysis of the available skeletal information.