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• Eunicid polychaetes have long, segmented bodies, and strong denticulated jaws.

• They are widely distributed in tropical to temperate shallow marine to shores.

• The “Bobbit worm” is one of the largest eunicids that fascinated the public.

• Burrowing “Bobbit worm” only extend a minor portion of their body outside of the sediment, thus observations on their behavior beneath the seafloor are difficult.

• However, the feeding behavior of this giant ambush-predator is amazing.

• “Bobbit worm” hides in burrow and explodes upwards snatching unsuspecting preys with their powerful jaws.

• The preys are still alive when the “Bobbit worm” pulls them into the sediment for consumption.

• Ancient predatory polychaetes have soft-tissue bodies resulting in an incomplete fossil record.

• Nothing is known about the burrows and behavior beneath the seafloor of these ancient polychaetes.

• Researchers used data from Miocene strata in northeast Taiwan to erect a new ichnogenus, Pennichnus.

• Ichnogenus is a group of trace fossils that is given a name because the similarity of the traces suggests they were made by closely related species of organisms.[1]

• Fossil length: 2 meters long

• Fossil diameter: 2 to 3 centimeter

• Fossil shape: L-shaped burrow

• The fossil has distinct feather-like structures around the upper shaft.

• A comparison of Pennichnus to other biologically similar organisms strongly suggests that this new ichnogenus is related with ambush-predatory worms that lived about 20 million years ago.

Sources:

Pan, YY., Nara, M., Löwemark, L. et al. The 20-million-year old lair of an ambush-predatory worm preserved in northeast Taiwan. Sci Rep 11, 1174 (2021). https://doi.org/10.1038/s41598-020-79311-0

[1] https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/ichnogenus

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