Cambrian Bivalved Arthropod Had Extremely Multisegmented Body

Balhuticaris voltae is the largest bivalved arthropod to date, at almost double the size of the previous record-holder, Nereocaris exilis.

Life reconstruction of Balhuticaris voltae.  Image credit: Hugo Salais.

Life reconstruction of Balhuticaris voltae. Image credit: Hugo Salais.

Balhuticaris voltae swam in the oceans of the Cambrian period approximately 506 million years ago.

At 24.5 cm (9.6 inches) long, the ancient animal is one of the largest Cambrian arthropods and the biggest bivalved arthropod known to date, with the closest being Nereocaris exilis and Tuzoia.

Balhuticaris voltae was likely a type of hymenocarine, a group of Cambrian arthropods that possessed bivalved carapaces and looked superficially like shrimps.

“Cambrian bivalved arthropods are a group of arthropods characterized by their cephalothoracic bivalved carapaces,” said University of Toronto paleontologists Alejandro Izquierdo-López and Jean-Bernard Caron.

“Many bivalved arthropods are known only from isolated carapaces, but fossils with soft tissue preservation are revealing an increasingly complex polyphyletic group, mostly comprising the stem-group euarthropod Isoxyidae and the Hymenocarina.”

“With 30-40 known species, hymenocarines are the more diverse of both groups, but their position in early arthropod evolution has been widely debated.”

Balhuticaris voltae had an extremely elongated and multisegmented body bearing ca. 110 pairs of homonomous biramous limbs.

The animal’s unusual carapace resembled an arch; it covered only the frontalmost section of the body but extended ventrally beyond the legs.

It had a complex sensory system and was probably an active swimmer thanks to its powerful paddle-shaped exopods and a long and flexible body.

“With a total of 110 post-cephalic segments, Balhuticaris voltae has the highest number of segments recorded among Cambrian arthropods, ”the researchers said.

“Multisegmentation (more than 20 segments) is widely present across Cambrian arthropod groups such as jianfengiids, marrellomorphs and in multiple trilobites.”

Balhuticaris voltae, holotype.  Image credit: Izquierdo-López & Caron, doi: 10.1016 / j.isci.2022.104675.

Balhuticaris voltae, holotype. Image credit: Izquierdo-López & Caron, doi: 10.1016 / j.isci.2022.104675.

Eleven specimens of Balhuticaris voltae were collected from the Marble Canyon area of ​​the famous Burgess Shale, a Cambrian-age fossil field in Canada.

Balhuticaris voltae is one of the biggest fully-preserved animals from the Burgess Shale and the Cambrian, ”the scientists said.

“The increasing ecological complexity of the Cambrian has long been recognized based on its planktonic communities or the filling of the pelagic zone and species such as Balhuticaris voltaethus, not only exemplify how gigantism in the Cambrian occurred in a wider number of groups than Radiodonta but also exemplify this increasing complexity of the Cambrian ecosystems. ”

The discovery of Balhuticaris voltae is reported in a paper published June 25, 2022 in the journal iScience.

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Alejandro Izquierdo-López & Jean-Bernard Caron. Extreme multisegmentation in a giant bivalved arthropod from the Cambrian Burgess Shale. iScience, published online June 25, 2022; doi: 10.1016 / j.isci.2022.104675

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