I believe that the Radzyner Rebbe, who was the one to reintroduce the concept of wearing techeles, thought that the techeles dye came from a certain squid. Later, Rav Hertzog, the first cheif rabbi of Israel, reviewed this position and cocnluded that the squid did not pass the tests laid out by the gemara in order to be real techeles (for instance the color would fade when instered into certain solutions.) After arriving at these results, Rav Herzog searched and found this snail (which is used by most of the techeles factories) that he felt passed all of the tests.
Remember that today when people see techeles on tzitzis it could either be from that squid (primarily used by Breslover chasidim) or the from the snail and that is the one that is endorsed by many of the litvishe rabbonim.