Cryptocleidus were aquatic long-necked reptiles, or plesiosaurs, that went extinct at the end of the Cretaceous period, in 65,000,000 B.C. However, it seems a number of the Cryptocleidus somehow survived extinction.
A Cryptocleidus appeared and attacked H.E.A.T.'s submarine until Zilla Junior appeared and started to fight it, just as H.E.A.T. discovers a Tachyon ship in the bottom of the ocean.
When H.E.A.T. get out of the Tachyon ship, another Cryptocleidus appears. Zilla Junior tries to evade them and eventually hits a rock formation, causing the two Cryptocleidus to be crushed by the rock slide.