Glochid

Glochids and spines on a species of Opuntia. The spines are the relatively large, radiating organs; the glochids are the fine prickles in the centres of the bunches.
Glochids (Opuntia microdasys monstrose)

Glochids or glochidia (sg.: "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 cactus species, each tuft containing hundreds of glochids; this may be in addition to, or instead of, the larger, more conspicuous cactus spines, which do not readily detach and are not generally barbed.