Symbiotic relationships, which involve two different kinds of organism interacting with close physical contact, are common in nature. However, few prehistoric examples involve soft-bodied animals because they are normally not fossilized.
Although fossils of the two species of marine worm, Cricocosmia jinnigensis and Mafangscolex sinensi, have been found before, these are the first reported examples to show other animals attached to them.
The smaller worm-like guests, a new species named Inquicus fellatus, are up to 3mm long and attached at their bottom ends to the stiff skin of their hosts, with their feeding ends pointing away.
espite the fact that Inquicus fellatus are attached to their host worms, there is little indication they were feeding by penetrating the skin of their hosts, causing the authors to conclude it was unlikely the relationship was directly parasitic.
Sarah Gabbott, Professor of Palaeobiology from the University of Leicester’s School of Geography, Geology and the Environment, said: “When we first saw the large worm curled around, almost hugging, lots of tiny worms, we suspected that we had uncovered an adult with offspring. But, careful inspection with a high-powered microscope, revealed that the large and small worms were different species — so that theory was completely blown away, and we realized that a symbiotic relationship was most likely.
“We then asked ourselves — was it parasitic or not — were the small worms feeding on the large one? We could tell that it was always the posterior of the small worms, and not the mouth, that was attached so this was altogether a more ‘neighborly’ relationship.”
Dr Greg Edgecombe from The Natural History Museum in London, a co-author on the study, says: “Evidence of symbiotic relationships are rare in the invertebrate fossil record, and this beautiful example shows how these associations began to develop as ecosystems became more complex in the Cambrian Period. But even beyond their scientific importance, what I find especially exciting about these fossils is that they give a pure snapshot of life and death hundreds of millions of years ago. It’s a moment of animals interacting, frozen in the rock.” Paper. (paywall) – Peiyun Cong, Xiaoya Ma, Mark Williams, David J. Siveter, Derek J. Siveter, Sarah E. Gabbott, Dayou Zhai, Tomasz Goral, Gregory D. Edgecombe, Xianguang Hou. Host-specific infestation in early Cambrian worms. Nature Ecology & Evolution, 2017; DOI: 10.1038/s41559-017-0278-4 More.
It will be interesting to know what the small worms were doing for the big ones. Surely, symbiosis ought to mean that the two species are doing something for each other, like birds cleaning the teeth of hippopotamuses.
See also: Life continues to ignore what evolution experts say
How much evolution can symbiosis account for?
Stasis: When life goes on but evolution does not happen