This is Siphusauctum gregarium, a creature that lived in the ocean 500 million years ago. It's so completely strange that it's taken scientists 30 years just to figure out how to describe it. It's literally like nothing else on Earth.
Siphusauctum gregarium is one of the so-called "problematica", a group of about twenty other similarly ancient organisms that defy any attempts to classify them. While the organism shares plenty of superficial qualities with other known species, zoologists can't find anything that is even remotely closely related to it. In a sense, these problematica are the closest thing to truly alien organisms that we've encountered — yes, they almost certainly share a common evolutionary heritage with all other organisms, but they're so strange that we can't even see the inklings of those connections.
That's all part of why this organism has remained largely ignored since its discovery back in 1983, despite the presence of over a thousand fossil specimens. It's only now that Canadian researchers Lorna O'Brien and Jean-Bernard Caron are attempting to describe it properly. Earth Times explains their findings, which were recently published in PLoS ONE:
Siphusauctum gregarium looked like a tulip, about 20cm (or 8ins) long, filter feeding from the floor of the sea. The body or "calyx" is enclosed by a sheath, with six small filtering holes and a terminal anus. It has a large stomach, followed by a conical gut and straight section of intestine. Six radially-symmetrical sections contain the filtering combs. A rapid movement of mud is likely to have covered the groups and created the fossils and the shale. Only the stomach, and anus of the digestive tract show any phylogenetic relationships, but exactly which relationship is up in the air. Hence the new family, new genus, new species, in fact, new everything.
Siphusauctum lived in huge clusters in the oceans of the Cambrian Period, which has been preserved in the fossil record thanks to the Middle Cambrian Burgess Shale of the Canadian Rockies. The organisms likely remained anchored to the sea floor, from which they dined on algae and whatever else came into its field of view. For more on the story of these truly bizarre organisms, check out Earth Times.
Original paper at PLoS ONE. Artist's conception by Marianne Collins.