Synalpheus microneptunus is a species of small snapping shrimp native to the waters off the island of Barbados. It is one of at least seven known species of eusocial shrimp. They are cryptofauna, living exclusively within the network of tunnels in the sponges Neopetrosia proxima and Neopetrosia subtriangularis. They form small colonies of six to fifteen individuals, usually with only a single breeding female.