Here we have a Cambrian Cnidarian, a jellyfish with tentacles from the famous Krukowski quarry in Central Wisconsin that is currently under intense scientific study that yields ichnofossils that are the earliest evidence of terrestrialization of animals in the fossil record. It is currently undescribed, though publication can be soon anticipated. The tentacle jellyfish are rare in the quarry that also produced large medusa forms, and this specimen is among a number recovered of a new layer, the first to be obtained in three years.

Being comprised entirely of soft tissue (living jellyfish are about 95 % water), unlike animals with exoskeletons (e.g., trilobites) or skeletons (vertebrates), jellyfish fossils are body fossils that are impressions of the jellyfish. Such fossil impressions are rare, especially from the Cambrian. Note that these jellyfish have tentacles in the familiar radial symmetry of all Cnidarians. Jellyfish were some of the most ferocious predators of the Cambrian marine environment. These fossils are almost surely the result of a mass stranding on an ancient Cambrian beach, possibly caused by a storm surge.

These jellyfish come from a particular horizon in the Mount Simon Sandstone formation that also yields facinating Diplichnites, huge Jellyfish (Medusae) and Climactichnites. Jelly fish body fossils are incredibly subtle, and therefore this specimen has been subtly stained.

Phylum Cnidaria (anemones, corals, jellyfish and sea pens) are among the most ancient animals and has one of the longest fossil histories of metazoans. Though simple in body form, they remain ubiquitous and widespread in modern marine environments. The earliest forms in the fossil record appear in Ediacarian fauna of Southern Australia, which dates to the Precambrian some 600 million years ago. This is clear testament that old and simple animals can be enormously successful.