From Lexicanum

Rending Claws are a Tyranid Bio-weapon.

In 4th Edition and 3rd Edition Rending Claws are short and powerful and often tipped with diamond hard shards to form a cutting edge. They are excellent at ripping through vehicles and heavy armour as well as flesh and bone, making them deadly to all while in combat.^1-p31

Sources

• ¹:Codex: Tyranids (4th Edition) (and Codex: Tyranids (3rd Edition) p8, identical entry in Warhammer 40,000: Wargear p56)