A hypothetical anomalocarid and its equally hypothetical commensals. First in a series.
Here I've postulated a group of anomalocarids that have developed a hermit crab-like habit of using discarded shells (in this case a Hercoceras nautiloid) as protective homes. This specimen is the Blue Squid-crab (Repticaris caerulea), a benthic animal that drags itself along using its first two sets of highly-modified lateral fins. Like Atlantic lobsters, the squid-crab is an opportunistic feeder, typically scavenging carcasses-- although it will occasionally catch live prey such as this Weinbergina opitzi (a real prehistoric animal and a relative of the horseshoe crab).
The squid-crab's shell also provides shelter for several other animals. Coin trilobites (Harpes denarius) live just inside the mouth of the shell, emerging occasionally to scavenge scraps from their host's meal. A boring sponge (Archaeocliona xanthos) often colonizes the upper parts of the shell. It's acidic burrowing frequently breaks all the way through to the interior camerae, providing shelters for the poisonous, brightly-colored trunk-squid (Cryptomonstrum nothopabinia), a relative of Tullimonstrum gregarium.
In addition to the speculative animals, I've also depicted here a couple of real-life prehistoric critters. The squid-crab is currently trudging through a forest of crinoids, composed primarily of Hapalocrinus and Bactrocrinites. Edging the open areas of the forest are several conularids and an abundance of edrioasters and seastars. Finally, in the upper right corner is the crinoid-eating pycnogonid Palaeoisopus.