 In the narrower sense, "Synalpheus" occur in the East Pacific where they are most plentiful and probably originated, and to a lesser extent in the Atlantic and the Indian Ocean; the species placed in "Zuzalpheus" occur mainly in the western Atlantic where their lineage probably originated, and to a lesser extent in the eastern Atlantic and Indian Ocean, and the East Pacific.It may thus be that the closure of the Isthmus of Panama in the Piacenzian (about 3 million years ago) was a key factor in separating the two lineages, as species referred to "Synalpheus sensu stricto" are most plentiful in the western Pacific.The snapping behaviour of "Synalpheus" is rather well studied.