Each predator has its own methods. Crabs break the shells by force. Various types of gastropods developed the ability to get into shells. The Muricidae bore through shells and consume prey. Some gastropods make holes in the shell and put in a paralysing or relaxing substance; others work on small cracks in the edge of the shell. Once they get their proboscis in, they eat the shellfish. Perhaps surprisingly, some sponges can also bore into shells. During the Mesozoic there were also a number of vertebrate predators of shellfish: the placodonts, and some ichthyosaurs and mosasaurs had flat shell-crushing teeth.