The phylum Mollusca arose during the so-called Cambrian explosion about 542 million years ago, during which time, over a period of 50 million years, new life forms emerged, including all the major animal orders that we have today. There are at least 85,000 living species of mollusks and at least as many extinct ones. Some mollusks have outer shells like clams and snails, others have rudimentary internal skeletons like ten-armed squids, and others, like eight-armed octopus, have no other hard parts than their beaks. All of these mollusks reproduce with eggs and therefore have roe.