A REVIEW OF THE CLASS SOLUTA (ECHINODERMATA): IMPLICATIONS OF A NEW AND YOUNGEST GENUS FROM THE MIDDLE DEVONIAN OF NEW YORK STATE

The “carpoid” echinoderm class Soluta (Cambrian, Stage 3 to Mid Devonian) is arguably the most primitive clade of the Echinodermata and is not ancestral to bilaterial echinoderms, nor did it give rise to pentameral classes. Solutans are nearly bilateral but never attain true symmetry. A single, free standing, feeding brachiole extends anteriorly from the lateral margin or from the upper face, on either side of the (usually) flattened polyplated ovoid theca. A posteriorly directed two-part stele, which probably served mainly for locomotion extends from the posterior margin. A polyplated or tetramerous proxistele provided lateral wagging of the thinner and longer biserial dististele, which resulted in tadpole-like wriggling locomotion along the bottom. Cambrian and Ordovician solutes are commonly found in siliciclastic/carbonate cemented sediments (claystone to muddy fine-grained sandstones) in sub wave base to quiet, deeper water settings (subtidal to mid shelf) in normal marine to partially dysaerobic conditions. Solutes are most diverse in the Upper Ordovician and are widely distributed (especially western Laurentia, Bohemia, Iberia, and Morocco). Solutes are greatly reduced in diversity following the Hirnantian Extinction event. A single Dendrocystitid (Claritacarpus, Lochkovian, Bois D’ Arc Fm.) is known. All other post-Hirnantian solutes belong to the Rutroclypeidae, including Dehmicystis, Ludlow, Spain and Emsian Hunsrück Slate, Germany; Rutroclypeus, Lower Dev., Victoria, Australia, and a new, undescribed and, to date, youngest solute genus from the Mid. Devonian (mid- Givetian) Erie County, New York. Rutroclypians are “banjo shaped” in marginal outline: they have a flattened, circular, polyplated theca with a high surface to mass ratio. A biserial brachiole extends anteriorly, its base inset from the anterior margin and to the right of the thecal axis. There is a well-defined tetramerous proxistele extending from an axially placed posterior embayment in marginal plates and a conjoined dististele, which is composed of elongated dimeres. Rutroclypians inhabited deeper water, near deep storm wavebase in muddy bottom offshore-mid shelf environments. Their ability to live in dysoxic muddy settings may be a key factor in allowing this solutan clade to survive the Hirnantian extinction event.