Evolution of gastropods are still not clear enough, and their taxonomy or scientific classification keep changing over time. There are about 50,000 to 85,000 mollusks that have got adapted to both marine and terrestrial habitats. Scientists think that Gastropods evolved from the Cambrian period which is 541-485.4 million years ago. Gastropods are commonly referred as snails and slugs whether marine, freshwater or terrestrial. According, to fossil records first ever known gastropods lived in the ocean of Cambrian period. During this time mollusks of the genera Strepsodiscus and Chippewaella developed to become the most primitive snails. By the Ordovician period mollusks underwent great diversification and gastropods started multiplying in number and species in aquatic habitats. Important thing to be noted is that although they increased in number they weren't prominent, they just colonized place to live in. During the Paleozoic era, gastropods were abundant in the sea. Some of them still exists as living fossils they show characteristics of that period. From the Mesozoic era many snails began to evolve and developed features present in current day living snails. At last due to increase in population these organisms started colonizing terrestrial region but still were not dominating.
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