Tricleidus is an extinct genus of cryptoclidid[1] plesiosaur known from only specimen (BMNH R3539) from the middle Jurassic of United Kingdom.

[2] It was first named by Andrews in 1909 and the type species is Tricleidus seeleyi.

[2] One species, T. svalbardensis,[3] was moved into Colymbosaurus in 2012.

[4] It was found in the Agardhfjellet Formation, Norway.

This article about a plesiosaur is a stub.