The kamayari (鎌槍, sickle spear) is similar to the jumonji yari. While it also had two protrusions shooting off the base of a main spear tip, in yari the offshoots were hooked back downward. The kamayari essentially is a yari with kama at the base of the blade to assist in hooking things. Generally the hooks are large enough to hold the head, neck or jaw (when in a tree) or to hook limbs of a swordsman on the ground, thus it is different in function in this respect from other types of yari. Also the kamayari was used to hook horsemen and dismount them.
Historically it also had a non military use, where it was employed by Japanese firemen to pull down the roofs of burning buildings to slow a fire much the same way firemen of today would topple buildings to create a firebreak.
There is also a single hooked variety of the kamayari called the katakamayari.