Scientists find new fossilised English species of parasitic tongue worm

By Culture24 Reporter | 21 May 2015

A 420 million-year-old species of  tongue worm parasite has been discovered still attached to the shell of its host

a computer generated image of a shell fish
A 425 million-year-old parasite: the pentastomid Invavita piratica (in orange) attached externally to the shell of its host (an ostracod). The ostracod is using its limbs to swim forward.© Siveter, Briggs, Siveter and Sutton
A new fossil species found in 425-million-year-old rocks in Herefordshire has been identified by scientists as an ancient parasitic intruder.

Several examples of the species - a type of 'tongue worm' with a soft body ranging from one to four millimetres - have been identified in the fossils, which scientists describe as exceptionally well preserved.

The species has a worm-like body, head and two pairs of limbs. Its descendants today live in the respiratory system of a host when eaten.

The ancient fosillised version of the grisly parasite was found still attached to its unfortunate host, a species of ostracod (a small sea creature) with two shells joined at a hinge.

Despite their name, tongue worms (technically termed pentastomids) are not worms at all but rather an unusual group of tiny and widespread parasitic arthropods. Today there are around 140 species of them and they can affect vertebrate animals, particularly reptiles and even humans.

Their fossils are exceptionally rare and until now are known only from a handful of isolated juvenile specimens.

a computerised image of small crustaceans
The 425 million-year-old pentastomid Invavita piratica and its host, the ostracod Nymphatelina gravida. • two pentastomids (in orange) attached externally to the ostracod •one of the pentastomids • the ostracod with its shell removed, showing the external pentastomids and a pentastomid near the eggs of the ostracod. © Siveter, Briggs, Siveter and Sutton
Professor David Siveter, of Leicester University, who made the discovery with colleagues from various universities across Europe, described the fossilised discovery as important due to the rarity of parasites in the fossil record and the possible host of fossil tongue worms. The origin of the lifestyle of tongue worms has been the subject of much debate.

“This discovery affirms that tongue worms were ‘external’ parasites on marine invertebrate animals at least 425 million years ago,” he explained.

“It also suggests that tongue worms likely found their way into land-based environments and associated hosts in parallel with the movement of vertebrates onto the land by some 125 million years later.”

The tongue worm and its host lived in a sea during the Silurian period of geological time. It would have covered much of southern Britain 425 million years ago, when the country was positioned in warm southerly subtropical latitudes.

Scientists have reconstructed the fossils using 3D computer modelling and named the new species Invavita piratica, meaning an "ancient intruder" and "piracy" - references to its parasitic lifestyle in the sea.  

The research, supported by The Natural Environmental Research Council, the Leverhulme Trust, the John Fell Oxford University Press (OUP) Research Fund and the Yale Peabody Museum of Natural History, has been published in the journal Current Biology.

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