Phylogenetic systematics of the Indo-Pacific heart urchin Metalia Gray, 1885

Abstract:

Irregular sea urchins of the clade Spatangoida, informally known as heart urchins, form a major and important component of tropical marine ecosystems. The spatangoid sea urchin genus, Metalia Gray 1885, a member of the spatangoid family Brissidae, is known primarily from the Indo-pacific region, although one species is known from the west coast of North America. Examination of new material is adding significantly to our knowledge of the morphology and taxonomy of Metalia. There are nine known species: Metalia spatagus (Linnaeus, 1758); Metalia sternalis (Lamarck, 1816); Metalia townsendi (Bell, 1904); Metalia nobilis Verrill, 1867-71; Metalia robillardi (de Loriol, 1876); Metalia dicrana H.L. Clark, 1917; Metalia latissima H.L. Clark, 1925; Metalia persica (Mortensen, 1940); Metalia angustus de Ridder, 1984; and Metalia kermadecensis Baker & Rowe, 1990. In addition, we have discovered two Philippines species new to science. Our work is presently removing ambiguities among characters used to typify all known Metalia, allowing for the establishment of more reliable species identification. A morphology-based phylogenetic analysis of Metalia using outgroup comparisons among brissid taxa such as Anametalia, Granobrissoides, Rhynobrissus, Brissopsis, Eupatatus, Meoma, and Brissus suggests that Metalia is monophyletic. An intriguing possibility is that the very distinctive and beautiful form from North America, Plagiobrissus, is very closely related to and possibly evolved from within Metalia. We are also studing various aspects of the biogeography and growth of Metalia.