Twenty-five randomly chosen 185/333 cDNA sequences from each species, H. erythrogramma and S. purpuratus, were aligned in ClustalW with default parameters and the alignment was further refined manually in BioEdit. Phylogenetic analyses were performed in PAUP*4.0b10 using character based, distance-based and model-based (Maximum Parsimony, MP; Neighbour-joining, NJ and Maximum Likelihood, ML) methods of analysis. For MP analysis, a heuristic search strategy was employed to identify the most parsimonious tree. All characters were treated as unordered and un-weighted. Bootstrap re-sampling based on 1000 replicates was used to assess the support of relationships for the majority-rule consensus tree. For the NJ and ML phylogenetic analyses MODELTEST v.3.06 was used to estimate the most likely model of sequence evolution for the sequence data. Based on the Akaike Information Criterion (AIC), Tamura-Nei (+G) was selected as the most likely model of sequence evolution for 185/333. Corrected genetic distances based on 2025 positions in the alignment were calculated in PAUP*4.0b10. NJ and ML trees were obtained in PAUP*4.0b10 using model parameters specified by MODELTEST and NJ was also assessed with 1000 bootstrap replicates.