Biologically, no, I don't know the difference. Linguistically, however, they both derive from Medieval French 'tortue,' which comes from the Latin 'tortura' (twisted), the past participle of the Latin verb 'torquere', meaning 'to twist.'

Both are related, through a complex line of descent, to the Modern English 'turd.' I kid you not.

See what a university education will do for you?

Rachel