Slow-Moving Animal, Hides in Its Shell

Word Meaning:

TORTOISE — Any of various land-dwelling reptiles, of the family Testudinidae (chiefly Canada, US) or the order Testudines (chiefly UK, Australia, New Zealand, Ireland, South Africa, India), whose body is enclosed in a shell (carapace plus plastron). The animal can withdraw its head and four legs partially into the shell, providing some protection from predators.

Definitions from Wiktionary.