1) Glochidium 2) Pricker 3) Prickle 4) Spine 5) Sticker 6) Thorn 1) Glochidium 
Glochids or glochidia (singular `glochidium`) are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family Opuntioideae. Cactus glochids easily detach from the plant and lodge in the skin, causing irritation upon contact. The tufts of glochids in the areoles nearly cover the stem surfaces of some cact.....
a barbed hair or bristle, e.g. the fine hairs in Opuntia.
A barbed hair or bristle. ... (09 Oct 1997) ... 
(glo´kid) a small barbed hair or bristle found on certain species of cactus, such as the prickly pears (species Opuntia), a common cause of mechanical irritant dermatitis.
a short hair, bristle, or spine having a barbed tip.