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A monotypic new genus,Coleicarpus, is proposed forCastericystis?sprinkleiUbaghs & Robison 1988, the only solute known to be attached when adult.Coleicarpus sprinkleiwas fixed by the tip of its stele or tail to trilobite exoskeletal fragments which themselves adhered to the sea bed. The tail ofC. sprinkleiis uniformly circular in cross-section and made of small non-imbricating plates which form imprecise transverse rings and longitudinal rows. The tail ofC. sprinkleiis not divided into discrete regions as are the tails of other solutes.C. sprinkleiis probably the most primitive known solute because of its attachment and lack of tail regions. These features of its tail are consistent with the theory of the descent of solutes from aCephalodiscus-like ancestor and also the phylogenetic placement ofC. sprinkleiin the stem group of the Dexiothetica, the monophyletic group which comprises the echinoderms and chordates exclusively. |
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