Hermit crabs were far from the first to call other creatures’ discarded shells their own — fearsome ‘penis worms’ did the same thing 500 million years ago, a study found.
Researchers led from Yunnan University presented new specimens recovered from the ‘Guanshan biota’, rock deposits that outcrop around Kunming city in China.
Guanshan is a famous deposit because it preserves not just shell material but soft tissue that could otherwise be lost in the fossil record.
Four of the phallic creatures — properly known as priapulid worms — were found preserved residing within the conical shells of hyoliths, a long-extinct fossil group.
After examining all possible explanations, they concluded that ancient worms had to seek shelter from predators. This was a surprising conclusion.
Guanshan biota worms lived only a few years after the Cambrian Explosion,’ a period that saw rapid diversification of animal life and complication.
The researchers claim that the research reveals how important predation is in shaping ecology and behavior of animals during this crucial period in human history.
Modern priapulids have never shown hermiting behavior.
Hermit crabs weren’t the first to call other creatures’ discarded shells their own — fearsome ‘ penis worms ‘ did the same thing 500 million years ago, a study has found. Pictured: an artist’s impression of a priapulid worm squatting in the discarded conical shell of a hyolith
They are well-known for their preservation of shell material and soft tissue that is often lost in fossil records. Pictured: a fossil of a priapulid worm (top) poking out of the shell of a hyolith
According to the researchers, each worm and the shell it inhabited corresponded in size — and no worm was found preserved without a shell — suggesting a biological association between the two.
Martin Smith, palaeontologist and paper author at the University of Durham, stated that worms always sit snugly in these types of shells. He also explained, “The worms are always sitting neatly within this same type of shells. In the same orientation and position.”
‘The only explanation that made sense was that these shells were their homes —something that came as a real surprise.
He said, “Not too long ago, these organisms were present, and there was nothing living more complex that seaweeds and jellyfish,” he added.
“So, it is mind-boggling to start seeing the complicated and dangerous ecologies often associated with younger geological periods so quickly after the arrival of the first complex animal.
The researchers also considered other explanations for the association between the worms and the shells — such as that the worms used the shells as temporary protection from the hostile conditions that buried and preserved them.
They said that it was difficult to reconcile the fact that the size of the worms in the shells was so similar that they were partially visible from the shells. Also, no shelter-seeking worms could be found.
Additionally, there wasn’t any evidence that emergency sheltering was occurring among other fossils in the same deposit.
According to the researchers, each worm and the shell it inhabited corresponded in size — and no worm was found preserved without a shell — suggesting a biological association between the two. Pictured is one of the fossilized worms the researchers analysed.
Four of the phallic creatures — properly known as priapulid worms — were found preserved residing within the conical shells of hyoliths, a long-extinct fossil group. Here is an artist’s impression of a Hyoltith Shell, although it was not occupied by the original owner.
Martin Smith of Durham University, paper author, said that the worms are always snugly inside the shells in the same positions and orientations. Pictured here: The worm is seen poking its head from the shell in the fossil.
The ‘hermiting’ lifestyle is known to have evolved in a diverse range of animal lineages — including not only hermit crabs but also the shrimp-like tanaids and both fauveliopsid and sipunculan worms.
Most of these creatures prefer to inhabit the discarded shells of gastropods, but some are also known to inhabit the shells and tubes of bristle worms, tusk shells and foraminifera.
Despite the broad distribution of this practice across the tree of life, however, it had never previously been seen in any organism living before 170 million years ago, during the so-called Mesozoic Marine Revolution.
Beginning some 210 million years ago, this ecological ‘arms race’ saw sea creatures develop adaptations against the evolution of shell-crushing and -boring predators.
All findings were published in Current Biology.
Yunnan University researchers presented new specimens from the Guanshan biota, which are rock deposits found around Kunming.