Hallucigenia sparsa is the name of a "velvet worm" or onychophoran known only from fossils in the  Cambrian Burgess Shale formation, found in the Canadian Rocky MountainsHallucigenia have long spiny legs projecting at right angles from a wormlike body, with claws at the end.  They also have long spiny projections coming out of their backs, also at 90-degree angles to each other.  This makes it look like a row of "X"'s connected by a central tube, making it look something...like...some...obscure piece of electronic equipment.  The following diagram may help, but again, it may not:

  \  \/ \/ \/ \/ \/ \/ \/  /
   / \/ \/ \/ \/ \/ \/ \/ \ m
  /  /\ /\ /\ /\ /\ /\ /\  \

The organism was named during studies of the Burgess Shale in the early 1980's.   At that time, the only Hallucigenia fossils known showed only the spiny protrusions on their back. The first reconstruction of a Hallucigenia from these fossils was upside down, resulting in an even more bizarre appearance for the creature than was the case.

Hallucigenia have some small tentacles on the ventral side at one end (the m), but their function is unknown.  To this day, scientists still cannot tell which end of a Hallucigenia is which, and only know which side is down from the claws at the ends of the creature's feet.