Trace fossils associated with predatory behavior, such as Piscichnus, are primarily produced by vertebrates including fish, rays, and marine mammals that extract prey by jetting water into the sediment 15, 16, 17, 18. Most of the existing trace fossils produced by polychaetes, such as Planolites, Rosselia, Cylindrichnus, and Arenicolites, represent deposit-feeding, detritus-feeding, or filter-feeding behaviors, rather than predatory ones 11, 12, 13, 14. Consequently, burrows of raptorial polychaetes could potentially occur in strata as old as the early Paleozoic. Polychaetes emerged early in the Cambrian, and jaws of possible raptorial worms have been described from early Paleozoic strata 9, 10. The still living animal is then dragged down into the burrow for consumption, and the desperate attempts of the prey to escape commonly leads to disturbance and collapse of the sediment around the burrow opening 7. When potential prey comes within striking distance, the Bobbit worm rapidly thrusts out of its burrow and grabs the prey with its eversible pharynx and sharp maxillae 6. Upon reaching sexual maturity, some Bobbit worms construct a permanent mucus-lined burrow in the seafloor 8, and some use an antenna to simulate a wormlike motion for attracting prey 7. They are ambush predators that feed on fish, bivalves, and other annelids 6, 7. As a result, previous studies mainly focused on anatomy and ethology of this and other eunicids 1, 3, 5, and little is known of their burrow morphology.īobbit worms can grow up to 3 m long and 2 cm in diameter 3, 5. However, because burrowing Bobbit worms only extend a minor portion of their body outside of the sediment, observations on their behavior beneath the seafloor are difficult. One of the largest eunicids, the so called “Bobbit worm” ( Eunice aphroditois), has fascinated the public since its appearance in November 2017 in British Broadcasting Corporation’s “Blue Planet II”. They are widely distributed in tropical to temperate shallow marine to intertidal environments in the Atlantic, Indian, and Pacific Oceans 1, 2, 3, 4. Similar content being viewed by othersĮunicid polychaetes (Family Eunicidae) are well-known for their long, segmented bodies, and strong denticulated maxillae 1.

A comparison of Pennichnus to biological analogs strongly suggests that this new ichnogenus is associated with ambush-predatory worms that lived about 20 million years ago. This trace fossil consists of an up to 2 m long, 2–3 cm in diameter, L-shaped burrow with distinct feather-like structures around the upper shaft.

Here we use morphological, sedimentological, and geochemical data from Miocene strata in northeast Taiwan to erect a new ichnogenus, Pennichnus. Although predatory polychaetes have existed since the early Paleozoic, their bodies comprise mainly soft tissue, resulting in a very incomplete fossil record, and virtually nothing is known about their burrows and behavior beneath the seafloor. The still living prey are then pulled into the sediment for consumption. They hide in their burrows until they explode upwards grabbing unsuspecting prey with a snap of their powerful jaws. The feeding behavior of the giant ambush-predator “Bobbit worm” ( Eunice aphroditois) is spectacular.

Worms that are ambush predators