Ones. It was the second oldest lifeform in the Edgeworld (after Sanctaphrax), and it was the Ancient One of Water. It resided at the bottom of Mirror of the Sky, the third of the Four Lakes. It was lovingly tended by the Crested Goblins of the north shore clan, who settled on the banks of Mirror of the Sky. Though incapable of true speech, the Great Blueshell Clam could transmit its thoughts to those who visited it, and impart its knowledge within them. However, the only person outside Four Lakes to ever visit the Great Blueshell Clam was Keris Verginix.
During the events of The Slaughterer's Quest, Keris visited the Great Blueshell Clam, and asked it if it knew where her father, Twig, had gone. The Great Blueshell Clam told her that her destiny lay at the Free Glades. It then covered her with clamdust, which she later used to seed the South Lake of the Free Glades.