tardigrada n in some classifications considered a separate phylum: microscopic arachnid-like invertebrates living in water or damp moss having 4 pairs of legs and instead of a mouth a pair of stylets or needlelike piercing organs connected with the pharynx Usage(s) If the rotifera and tardigrada regained life, Voltaire could see no reason why they should not acquire new souls. Synonym(s) Tardigrada class Tardigrada