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As early as 1954, icefish were noted as possessing nearly transparent blood, lacking both erythrocytes and hemoglobin. Vertebrate existence has mostly been associated with possession of hemoglobin; however, a Neopagetopsis spp have evolved to survive without. One study investigated the genetic structure of alpha- and beta-globin genes in icefish as well as closely related species. Findings revealed a conserved deletion of globin genes in 15 of 16 species, though the remaining one presented an interesting case. Species N. ionah possessed complete globin gene sequences, but they aren’t functional. It is hypothesized that the two globin gene forms arose from an ancient hybridization event between an ancestral icefish and some other Nototheniid. Then due to lineage sorting of this polymorphism, N. ionah came to uniquely acquire its globin gene form.