Implications from a 28S rRNA gene fragment for the phylogenetic relationships of halichondrid sponges (Porifera: Demospongiae)

Halichondrida is a pivotal demosponge order of which the classification underwent major changes in the recent history. The monophyly of this order and its intra-ordinal phylogeny cannot be reliably determined on the basis of morphology. Here we present a 28Sr RNA gene tree of selected halichondrids, which supports the hypothesis of halichondrid non-monophyly and elucidates further inter-ordinal relationships. We enlarged the analysis by previously published sequences, discuss how previous analyses suffer from taxon bias and analyse the resulting phylogenetic implications. Most halichondrid families (in particular Axinellidae und Dictyonellidae) cluster polyphyletic and the molecular classification of several genera does not agree with the current (morphological) system.