leucosoidZool.|ˈl(j)uːkəsɔɪd| [f.mod.L. Leucos-ia (f.Gr. λευκός white) the name of the typical genus + -oid.] One of a family belonging to the tribe Oxystomata or pointed-mouth crabs. 1852Dana Crust. i. 48 But in the Leucosoids, there is a higher perfecting of the branchial system.