Castellanos, L.; Zea, S.; Osorno, O.; Duque, C. 2003. Phylogenetic analysis of the order Halichondrida (Porifera, Demospongiae), using 3Beta-hydroxysterols as chemical characters. Biochemical Systematics and Ecology 31: 1163-1183.
To analyze and extract phylogenetic information from chemical characters, the 3b-hydroxysterol composition of 12 sponge species of various families of the Poriferan order Halichondrida (sensu lato), was determined. The current definition of the order is ambiguous, and its classification remains in a state of flux and hence, further chemical characters may aid in stabilizing it. Axinella corrugata, Pseudaxinella reticulata, P. explicata, Ptilocaulis walpersi, Dragmaxia undata (family Axinellidae), Myrmekioderma rea, M. gyroderma (family Desmoxyidae), Scopalina ruetzleri (family Dictyonellidae), Halichondria lutea, H. magniconulosa, Topsentia ophiraphidites and Petromica ciocalyptoides (family Halichondriidae) were collected in the Santa Marta area, Colombian Caribbean. Cladistic principles were used to advance a hypothesis of genealogical relationship among the studied species and to contrast current classifications at various taxonomic ranks. Sterol identity and various sterol properties (number of carbons, nuclei type, saturations and substitutions of the lateral chain) were coded as discrete characters according to their relative abundance in 4% ranges, for each of the studied species, and for an out group of 41 species of nine orders whose sterol fractions had been published. Of more than 300 codified characters, 74 constituted unique evolutionary novelties within the studied in group. Fifty-one of these characters (including 15 sterols) uniquely defined six species. Twelve sets of novel characters were shared exclusively by two or more species of the studied group and were thus informative in a phylogenetic sense. The cladogram, built by hand, had seven characters that were compatible with each other and were shared by two or more species (i.e. synapomorphies) and five that were incompatible with two or more. Howeverfew, these seven characters can be used to advance and contrast falsifiable hypotheses of phylogeny. There was not a sterol character unique for the order Halichondrida s.l. At the
family level, only Desmoxyidae had a sterol synapomorphy, but it needs confirmation as only species of Myrmekioderma were studied. The only clear familial relationship was the existence of a unique synapomorphy for a group formed by the studied Axinellidae and Dictyonellidae, which contradicts relationships hypothesized from morphological characters. At a lower taxonomic rank, there were unique synapomorphies relating the studied species of Myrmekioderma and of Pseudaxinella. In contrast, Halichondria was evidently polyphyletic from sterol data, although three out of four Halichondriidae species were related by a unique sterol property.