Systematics, phylogeny and biogeography of the genusMellita(Echinoidea: Clypeasteroida)

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Abstract
The genus Mellita is an assemblage of New World tropical to temperate lunulate sand dollars (Mellitidae). Multivariate analysis of morphometric data, representing specimens from Nantucket to Brazil, indicates the presence of three allopatric Atlantic species. The taxonomic history of Atlantic species has been traced from 1734 to the present. The following revisions of the Atlantic taxa are necessary: (1) Mellita isometra sp. nov., restricted to the east coast of North America, from Nantucket to Florida; (2) M. tenuis Clark, 1940 (west Florida to Louisiana) raises a previously described variety to species level. The type species, M. quinquiesperforata (Leske, 1778) occurs from Louisiana to Brazil, including the Greater Antilles. Within the Pacific there are distinct species with extensively overlapping distributional ranges: M. longifissa Michelin, 1858; M. grantii Mortensen, 1948; M. notabilis Clark, 1947 and M. kanakoffi Durham, 1961. The Atlantic species do not form a monophyletic group. Phylogenetic analysis shows that the southerly form, M. quinquiesperforata, is the sister group to a monophyletic group containing all of the Pacific species. The species of Mellita have probably originated through vicariance of a wide-spread ancestral biota in the late Neogene.