Evolution & Systematics

The gastropods are the largest class within the Molluscs and are also the most diverse in that Phylum (Ruppert et al., 2004). They are an ancient class with the fossil record dating their origin to the early Cambrian Period (570 million years ago) (Ruppert et al., 2004). Gastropods are thought to have evolved from an ancestral monoplacophoran (also a Mollusc) undergoing torsion within it's shell, a feature which is a defining characteristic of modern gastropods (Ruppert et al. 2004). Abalone shells are subject to significant morphological plasticity depending on the environment that they inhabit, making use of the fossil record difficult to examine radiations and speciations within the Family (Geiger and Groves, 1999; Geiger and Poppe, 2000).

The Family Haliotididae belong in the Vetigastropoda Clade which is a subdivision within the Order Archaeogastropoda due to a number of morphological features including a nacreous shell with a specific cleavage pattern (van den Biggelaar, 1996), two bipectinate ctenidia (gills) with bursicles and a heart which pumps via two atria to the ctenidia (Geiger and Poppe, 2000).

Until the beginning of the twenty-first century the classification and phylogeny of the genus Haliotis had been made by the observation of characteristics of specimens, primarily differences and trends in shell morphology (Geiger and Groves, 1999; Geiger and Poppe, 2000). Recent advances in the use of molecular genetics will allow a detailed examination of the evolution and systematics of these organisms and may provide insight into their radiation and speciation.

The precise phylogenetic positions of the three Indo-Pacific abalone species, Haliotis asinina, Haliotis ovina and Haliotis varia are not currently resolved despite the use of modern molecular genetic techniques (Harasewych et al., 1997; Geiger and Poppe, 2000; Degnan et al., 2006). A modern synthesis by Degnan et al. (2006) based on mitochondrial DNA COII (mtDNA) sequences places H. asinina and H. ovina as sister taxa, with H. varia as sister to that pair, with these three tropical species having split from the temperate species. 

Phylogenetic tree showing the position of H. ovina in relation to the other two Indo-Pacific Haliotis
species based on COII mtDNA analysis. Modified from Degnan et al. (2006).​