title: A sclerite-bearing stem group entoproct from the early Cambrian and its implications.
abstract: The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans.
authors: Early Life Institute, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China. elizf@nwu.edu.cn
authors: Zhifei
authors: Z
authors: Zhang
authors: Lars E
authors: LE
authors: Holmer
authors: Christian B
authors: CB
authors: Skovsted
authors: Glenn A
authors: GA
authors: Brock
authors: Graham E
authors: GE
authors: Budd
authors: Dongjing
authors: D
authors: Fu
authors: Xingliang
authors: X
authors: Zhang
authors: Degan
authors: D
authors: Shu
authors: Jian
authors: J
authors: Han
authors: Jianni
authors: J
authors: Liu
authors: Haizhou
authors: H
authors: Wang
authors: Aodhán
authors: A
authors: Butler
authors: Guoxiang
authors: G
authors: Li
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005580:Fossils; D007448:Invertebrates / Q000033:anatomy & histology* / Q000145:classification / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D013997:Time Factors