Animals Arbacia Arbacia spatuligera DNA Primers DNA sequence DNA, Mitochondrial Echinoidea Electron Transport Complex IV Evolution, Molecular Hybridization, Genetic Isthmus of Panama Molecular Sequence Data Panama Phylogeny Phylogeography Sequence Analysis, DNA Species Specificity animal article classification cytochrome c oxidase gametic isolation molecules genetics hybridization marine barriers mitochondrial DNA molecular evolution molecular genetics nucleotide sequence phylogeny