ABSTRACT
Analysis of a fragment of the COI gene suggests that populations of the brittle star Ophiactis simplex, O. rubropoda, and a Texas ophiactid share a recent evolutionary history and may be in the process of speciation (Christensen et al. 2008). All of the populations included in the study produce the respiratory pigment hemoglobin that is contained in coelomocytes present in the water vascular system (O. simplex: Christensen 1998, O. rubropoda: Ruppert and Fox 1988, Texas ophiactid: Christensen 2004). While hemoglobins of various organisms are thought to share a common evolutionary origin (Hardison 2001), the amino acid sequence of closely related species typically share less than 50% homology (Kapp et al. 1995). Hemoglobin genes of vertebrates and many invertebrates typically have a two intron-three exon structure. The position of these two introns is conserved, occurring at positions B12 (intron 1) and G7 (intron 2) of the protein (Hardison 1998). The sea cucumber Caudina arenicola has a third intron occurring in the codon for amino acid nine (Kitto et al. 1998). An investigation into the nucleotide sequence of the hemoglobin gene and its structure was undertaken to further examine the relationship between these three closely related ophiactid species.
