Emerita rathbunae

Emerita rathbunae
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Family:	Hippidae
Genus:	Emerita
Species:	E. rathbunae
Binomial name
Emerita rathbunae Schmitt, 1935

External identifiers for Emerita rathbunae
Encyclopedia of Life	4265205
NCBI	101206
WoRMS	467699

Emerita rathbunae is a species of "mole crabs" or "sand crabs" in the genus Emerita that lives along the tropical Pacific coasts of the Americas.

E. rathbunae exhibits an extreme form of sexual dimorphism, with tiny neotenous males attaching themselves to the female's appendages, "thus carrying the tendency for small males in this genus almost to the verge of parasitism". Sexually mature females are typically 33–44 mm (1.3–1.7 in) in carapace length, while males are only 2.5–3.0 mm (0.10–0.12 in).

E. 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. 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.

Despite their sympatry, the closest relative of E. rathbunae is not E. analoga; rather, E. rathbunae is part of a clade that also includes species from the western Atlantic Ocean, including E. portoricensis and E. benedictii. 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.

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. The specific epithet rathbunae commemorates the American carcinologist Mary J. Rathbun.

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