REASSESSMENT OF HOMOLOGY OF MORPHOLOGICAL CHARACTERS IN TETRACTINELLID SPONGES BASED ON MOLECULAR-DATA

In sponges, as in other taxa with simple organization, the evaluation and use of morphological characters is difficult. Phylogenetic analysi s of the first 850 nucleotides from the 5' end of the 28S rRNA gene is used here to assess the homology of spicules used in the classificati on of the subclass Tetractinellida. A single well-supported MP tree wa s obtained. The monophyly of the nine Tetractinellida species studied confirms the tetraxon megasclere as a morphological synapomorphy for t he Tetractinellida. Two species are reallocated, Penares helleri as a Geodiidae, now thought to have lost sterraster microscleres, and Stryp hnus mucronatus to the Streptosclerophorida. SEM micrographs of Stryph nus microscleres show that the morphology of the sanidasters is Compat ible with the hypothesis that they are homologous with streptoscleres and confirm this reallocation. Two other synapomorphies are confirmed within the tetractinellid clade, the simultaneous presence of tetraxon megasclere and aster-type microsclere (Astrophorida) and the loss of the streptosclere and persistence of the euaster s.s. microscleres (Eu astrophorida) evidenced by the reallocation of Stryphnus mucronatus. T he streptosclere microscleres cannot be evaluated in terms of homology because Streptosclerophorida may be paraphyletic (although these node s are not supported by reliable bootstrap proportions) contrary to the currently accepted classification.