Ricinulei are small, slow and blind or nearly so, with a thick dark cuticle. The cucullus, the hood that gives the group its name, is a hinged plate at the front of the body that can be raised to feed and lowered to shield the chelicerae. The abdomen is coupled to the cephalothorax by a locking mechanism that clamps the two parts together.
Sperm transfer uses modified segments on the male's third legs, an arrangement not found in other arachnid orders. Females carry a single large egg beneath the cucullus for a period before it hatches, and the young pass through a six-legged larval stage before acquiring the adult complement of eight.
The order is genuinely obscure. Fewer than a hundred living species are described, they are known mainly from Neotropical and West African leaf litter and caves, and there is a rich Carboniferous fossil record indicating the lineage is over 300 million years old. Basic natural history for most species, including diet and lifespan, remains largely unrecorded.