Swarms of ‘em sitting in muck of still waters and sticks on you and drinks blood...as leeches do. They hate dryness and needs moisture, and I suppose the similarity ends there.
Unlike leeches, these little bastards comes with a mouth on both the anterior and posterior sides. Not sure where the posterior one leads.
Speculation (by me) goes that since the area is fulled of tonne-plus megafaunas, the leeches gets a feast whenever one comes by. If they had an anterior mouth for feeding, the posterior mouth could lead to a separate blood sac that it could regurgitate for its young(s).
Maybe their saliva can be harvested for anticoagulant.