These strange creatures are near relatives of the Mentiribrachia I showed you the last time (thanks for all the name suggestions, the new version is now online.
Fractalopods are scavengers walking over the seabed, seemingly, sideways on the search for dead aniamls, but also plants which sink from the swimming forests over their... bodies (they have no head in the classic definition).
Bigger carcasses are often full of these creatures which bite small canyons in the so much larger pseudoathropods and vertebrates.
Because they are also not invulnerable some species have toxic spikes at their flanks, like Spinolatus shows here. But how could these animals warn the predators? even a single bite could kill both, the predator and the prey. In the deeps of Xibalba colors are unimportant (but a few populations also live near the surface) and the mostly eyeless vertebrates can't recognize the form exactly. One of their best senses is the lateral line system which they use to detect the bioelectricity of animals. So the fractalopod produce a electric field which is stronger than that of an creatures of this size normally is.
Other genera solve the problem by producing as much offspring as possible.
When you want to know one of my inspirations for this creatutures look at Theo Jansens work: www.strandbeest.com/