The purple sea star, Pisaster ochraceus, lives in rocky intertidal and subtidal habitats along the U.S. west coast. Originally it was thought to be a distinct species from a similar orange sea star that lived in the same habitat, until genetic analyses confirmed that the two are simply different color morphs of the same species. What species concept was used originally?
a. Morphological species
b. Biological species
c. Geneological species
d. Phylogenetic species