Insights gained from the chemical composition of spicules in Haplosclerida (Porifera, Demospongiae)

The shape and arrangement of skeletal structures (spicules) in marine sponges are used in their taxonomic classification but shared spicule patterns often do not correspond to relationships postulated by molecular data, particularly for members of the order Haplosclerida. A chemical and spectroscopic analysis of spicules using FTIR-ATR (Fourier transform infrared spectroscopy), ICP-OES (inductively coupled plasma-optical emission spectrometry) and ICP-MS (inductively coupled plasma-mass spectrometry) was undertaken for nine Haliclona species from Irish and Mediterranean coasts to determine whether the chemical composition of the spicules could reflect a phylogenetic signal. The analysis indicates differences in the amounts of major and minor elements present in spicules across the nine species but differences do not reflect phylogenetic relationships. H. indistincta (a shallow sublittoral species) harbours much higher amounts of some elements in the spicules than the remaining (subtidal) species with H. viscosa showing much higher levels of zinc.