A survey for biochemical synapomorphies to reveal phylogenetic relationships of halichondrid demosponges (Metazoa: Porifera)

Biochemical compounds are a suggested alternative for morphological characters in sponge systematics. The monophyly of the crucial demosponge order Halichondrida is still largely unresolved. Here, we performed a search for synapomorphies, which might aid to define the order and its five families Axinellidae, Bubaridae, Dictyonellidae, Desmoxyidae and Halichondriidae. We also investigated possible links of the order Halichondrida with other demosponge taxa such as suberitids (Hadromerida). Our survey of published compounds revealed hydroxy-nor-sterols as a potential synapomorphy for axinellid taxa, 2,3,6 sulfated sterol nuclei as possible connection between Agelasida and Halichondrida, besides the known pyrrol-2-carboxylic acids and galactosylceramides, furthermore carbonimidic dichlorides, pupukeananes, diterpene isocyanides for the order Halichondrida and linear and cyclic diterpenes for the family Desmoxyidae. The suitability of biochemical characters in systematics is discussed.