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Naked chancelloriids from the lower Cambrian of China show evidence for sponge-type growth.


ABSTRACT: Chancelloriids are an extinct group of spiny Cambrian animals of uncertain phylogenetic position. Despite their sponge-like body plan, their spines are unlike modern sponge spicules, but share several features with the sclerites of certain Cambrian bilaterians, notably halkieriids. However, a proposed homology of these 'coelosclerites' implies complex transitions in body plan evolution. A new species of chancelloriid, Allonnia nuda, from the lower Cambrian (Stage 3) Chengjiang Lagerstätte is distinguished by its large size and sparse spination, with modified apical sclerites surrounding an opening into the body cavity. The sclerite arrangement in A. nuda and certain other chancelloriids indicates that growth involved sclerite addition in a subapical region, thus maintaining distinct zones of body sclerites and apical sclerites. This pattern is not seen in halkieriids, but occurs in some modern calcarean sponges. With scleritome assembly consistent with a sponge affinity, and in the absence of cnidarian- or bilaterian-grade features, it is possible to interpret chancelloriids as sponges with an unusually robust outer epithelium, strict developmental control of body axis formation, distinctive spicule-like structures and, by implication, minute ostia too small to be resolved in fossils. In this light, chancelloriids may contribute to the emerging picture of high disparity among early sponges.

SUBMITTER: Cong PY 

PROVIDER: S-EPMC6030521 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Naked chancelloriids from the lower Cambrian of China show evidence for sponge-type growth.

Cong Pei-Yun PY   Harvey Thomas H P THP   Williams Mark M   Siveter David J DJ   Siveter Derek J DJ   Gabbott Sarah E SE   Li Yu-Jing YJ   Wei Fan F   Hou Xian-Guang XG  

Proceedings. Biological sciences 20180601 1881


Chancelloriids are an extinct group of spiny Cambrian animals of uncertain phylogenetic position. Despite their sponge-like body plan, their spines are unlike modern sponge spicules, but share several features with the sclerites of certain Cambrian bilaterians, notably halkieriids. However, a proposed homology of these 'coelosclerites' implies complex transitions in body plan evolution. A new species of chancelloriid, <i>Allonnia nuda</i>, from the lower Cambrian (Stage 3) Chengjiang Lagerstätte  ...[more]

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