What does Tekhelet come from?

The Talmud describes Tekhelet as coming from a sea-creature called a chilazon. In a homiletic passage, the chilazon is characterized as “similar to the sea, being similar to [but not] a fish, and coming up from the sea once in seventy years [rarely].” Chilazon in modern Hebrew means “snail”. Rabbinic, historical, archaeological and chemical evidence point to Murex trunculus snails as the source of Tekhelet.