New edrioasteroid (Echinodermata) from the Spence Shale (Cambrian), Idaho, USA: further evidence of attachment in the early evolutionary history of edrioasteroids

A new species of Totiglobus, T. spencensis (class Edrioasteroidea, order Edrioasterida), is reported from the Spence Shale (Cambrian: Miaolingian Series, Wuliuan Stage) of eastern Idaho. The holotype, which was evidently buried at the base of a tempestite bed, is attached by a basal disk to a hyolithid conch. In contrast to the closely related species T. nimius, which attached to mat-stabilized sediment by means of a suction disk on the aboral surface, T. spencensis attached to hard substrates by means of an attachment disk on the aboral surface. Edrioasteroids first evolved mechanisms for attaching to hard substrates in the Wuliuan Age, and T. spencensis is thus among the earliest-known edrioasteroids to show this habit. By the Drumian Age, attachment to hard substrates had become the dominant post-larval life habit of edrioasteroids.