In the narrower sense, Synalpheus occur in the eastern 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 eastern 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.

[5] The only known eusocial aquatic species occur within the genus Synalpheus.

The species known to be eusocial are S. brooksi, S. chacei, S. elizabethae, S. filidigitus, S. rathbunae, S. regalis,[2] S. microneptunus,[6] and S. duffyi as well as potentially S.

[8] Eusociality is thought to have arisen due to competition for space, because among the species that host Synalpheus, empty sponges are rarely found.