Cambrian Sessile, Suspension Feeding Stem-Group Ctenophores and Evolution of the Comb Jelly Body Plan

Yang Zhao, Jakob Vinther*, Luke Parry, Fan Wei, Emily Green, Davide Pisani, Xianguang Hou, Gregory D. Edgecombe, Peiyun Cong

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

10 Citations (Scopus)
22 Downloads (Pure)

Abstract

The origin of ctenophores (comb jellies) is obscured by their controversial phylogenetic position, with recent phylogenomic analyses resolving either sponges or ctenophores as the sister group of all other animals. Fossil taxa can provide morphological evidence that may elucidate the origins of derived characters and shared ancestries among divergent taxa, providing a means to “break” long branches in phylogenetic trees. Here we describe new fossil material from the early Cambrian Chengjiang Biota, Yunnan Province, China, including the putative cnidarian Xianguangia, the new taxon Daihua sanqiong gen et sp. nov., and Dinomischus venustus, informally referred to as “dinomischids” here. “Dinomischids” possess a basal calyx encircled by 18 tentacles that surround the mouth. The tentacles carry pinnules, each with a row of stiff filamentous structures interpreted as very large compound cilia of a size otherwise only known in ctenophores. Together with the Cambrian tulip animal Siphusauctum and the armored Cambrian scleroctenophores, they exhibit anatomies that trace ctenophores to a sessile, polypoid stem lineage. This body plan resembles the polypoid, tentaculate morphology of cnidarians, including a blind gastric cavity partitioned by mesenteries. We propose that comb rows are derived from tentacles with paired sets of pinnules that each bear a row of compound cilia. The scleroctenophores exhibit paired comb rows, also observed in Siphusauctum, in addition to an organic skeleton, shared as well by Dinomischus, Daihua, and Xianguangia. We formulate a hypothesis in which ctenophores evolved from sessile, polypoid suspension feeders, sharing similarities with cnidarians that suggest either a close relationship between these two phyla, a striking pattern of early convergent evolution, or an ancestral condition for either metazoans or eumetazoans. The origin and interrelationships of comb jellies (ctenophores) have been subject to much recent debate. Zhao et al. describe several fossil forms related to ctenophores. They trace comb rows back to tentacular organs surrounding the mouth of a polypoid ancestor. These fossils support a ctenophore affiliation with cnidarians in the animal tree of life.

Original languageEnglish
Pages (from-to)1112-1125.e2
Number of pages14
JournalCurrent Biology
Volume29
Issue number7
Early online date21 Mar 2019
DOIs
Publication statusPublished - 1 Apr 2019

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Keywords

  • “dinomischids”
  • Dinomischus
  • Ctenophora
  • Cambrian
  • Coelenterata
  • Metazoa
  • Chengjiang

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