[2] Emerita rathbunae is found on the shores of the eastern Pacific Ocean, from the southern end of the Gulf of California in Mexico to Iquique in northern Chile, including the Galápagos Islands.

[3] In the south of its range, E. rathbunae co-occurs with the southern population of E. analoga, which occurs as far north as mainland Ecuador.

[4] The last common ancestor of the genus is thought to have lived in the Pacific Ocean, and to have colonised the Gulf of Mexico when the Isthmus of Panama was submerged, and E. rathbunae is thought to have similarly recolonised the Pacific from ancestors that lived on the Atlantic side of the Isthmus of Panama.

[4] Emerita rathbunae was described by Waldo L. Schmitt in 1935; the type locality was Punta Chame in Panama, and the holotype was deposited in the United States National Museum as specimen USNM 47887.

[6] Based on comparisons with other Emerita species, E. rathbunae is thought to be a very capable swimmer, and to burrow rapidly into the sand.