The Opiliones Internet Discussion Group provides a forum for the discussion of all aspects of Opiliones. Anyone interested in these animals is welcome to participate. Currently, there are no archives or digests, and the list is not moderated. Yes, Phalangida is an old scientific name for Opiliones. Opiliones is the currently preferred usage, but you may still find these animals referred to as Phalangida in older and some recent literature.
Spiders are also arachnids.
Spiders have waist, Harvestmen do not. However, some have sharp spines that can cause bleeding. Some also can pinch hard with their back legs and cause considerable pain. These spines are especially found in males of some larger species in South America. Maybe and No.