The shell of this mussel resembled that of modern scallops. Like them, Neithea lived on the ocean floor and, when threatened, could move by snapping its shell shut with such force that it created a stream of water which propelled the animal backward — a quick, but inexact method of fleeing enemies.
Eryon was an early ancestor of crabs and lobsters. It was a large crustacean with rather small claws that were probably used to catch small, soft animals, or to eat dead animals on the ocean floor. Eryon was able to crush only the very smallest snail shells.
This crab claw was adapted for crushing hard shells. That is indicated by, among other things, the large knobs on the insides of the claw fingers, which helped to crush hard objects. The tips of the claws were curved and overlap so that they did not get in the way of each other when the claw closed.
Avitelmessus was one of the largest crabs of the Cretaceous. Its body was flat, and some fossils have preserved colour patterns which indicate that the animal was camouflaged.
It lived on open muddy or sandy areas of the ocean floor, near the shoreline. Avitelmessus was a swift hunter and probably fed on worms, small snails and other invertebrate animals.
These snails are best known for their deadly poison. They also had adaptations which made it difficult for predators to get at their soft internal parts. The outside of the shell was so smooth that crabs, for example, had difficulty grasping it with their claws. The shell opening was also very narrow, and thus difficult for crabs to penetrate with their claws.