|the worm-like animal Inquicus fellatus, infesting Cricocosmia jinningensis, a marine worm.|
Cong, Ma, Williams, Siveter, Siveter, Gabbott, Zhai, Goral, Edgecombe & Hou, 2017
Symbiotic relationships are widespread in terrestrial and aquatic animals today, but evidence of symbiosis in the fossil record between soft-bodied bilaterians where the symbiont is intimately associated with the integument of the host is extremely rare. The radiation of metazoan life apparent in the Ediacaran (~635–541 million years ago) and Cambrian (~541–488 million years ago) periods is increasingly accepted to represent ecological diversification resulting from earlier key genetic developmental events and other innovations that occurred in the late Tonian and Cryogenian periods (~850–635 million years ago). The Cambrian has representative animals in each major ecospace category, the early Cambrian in particular having witnessed the earliest known complex animal communities and trophic structures, including symbiotic relationships. Here we report on newly discovered Cricocosmia and Mafangscolex worms that are hosts to aggregates of a new species of tiny worm in the lower Cambrian (Series 2, Stage 3) Chengjiang Lagerstätte of Yunnan Province, southwest China. The worm associations suggest the earliest known record of aggregate infestation of the integument of a soft-bodied bilaterian, host specificity and host shift.
|Fig. 1: Cluster of Inquicus fellatus attached to Cricocosmia jinningensis. a, C. jinningensis (YKLP 13226a) with a minimum of 12 attached I. fellatus (YKLP 13235–13246) on the ventral side. Scale bar: 3 mm.|
Inquicus fellatus gen. et sp. nov.
Etymology. Genus name from inquilinus (Latin) meaning a ‘lodger’ or ‘dweller in another’s house’, plus priscus ‘ancient’. Species from fellator ‘a sucker’ and atus ‘provided with’, alluding to its lifestyle.
Holotype. YKLP 13235 (part and counterpart). A complete speci-men, 3.3 mm long, attached to a Cricocosmia jinningensis specimen, YKLP 13226. Eleven other specimens of I. fellatus (YKLP 13236–13246) are attached to this host.
Locality. Ercaicun (type locality), Haikou, Kunming, Yunnan Province, China.
Horizon. Yu’anshan Member, Chiungchussu Formation, Eoredlichia–Wutingaspis trilobite biozone, Nangaoan Stage of Chinese regional usage, Cambrian Series 2; Stage 3 (ref. 1).
Diagnosis for genus (monotypic) and species. Small, ‘bowling-pin’-shaped worm with a sub-circular-shaped attachment disc at the posterior end of the body and a through gut that is funnel-shaped anteriorly. At the end of the gut near the attachment disc, there is a tiny sub-circular structure, interpreted as the urogenital opening or anus.
|Artist's reconstruction of the worm-like animal Inquicus fellatus, infesting Cricocosmia jinningensis, a marine worm that lived in seafloor sediments more than 500 million years ago.|
Illustration: Bob Nicholls PaleoCreations.com
Peiyun Cong, Xiaoya Ma, Mark Williams, David J. Siveter, Derek J. Siveter, Sarah E. Gabbott, Dayou Zhai, Tomasz Goral, Gregory D. Edgecombe and Xianguang Hou. 2017. Host-Specific Infestation in early Cambrian Worms. Nature Ecology & Evolution. DOI: 10.1038/s41559-017-0278-4
One of the earliest examples of a symbiotic relationship between invertebrates has been found in 520-million-year-old fossils from China.