''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.

Description

''Emerita rathbunae'' exhibits an extreme form of sexual dimorphism, with tiny

neotenous Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compa ...

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 in

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

length, while males are only .

Distribution and taxonomy

''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. 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 In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...

, the closest relative of ''E. rathbunae'' is not ''E. analoga''; rather, ''E. rathbunae'' is part of a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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 The Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country ...

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 Waldo LaSalle Schmitt (June 25, 1887 – August 5, 1977) was an American biologist born in Washington, D.C. He received his Ph.D. from George Washington University in 1922. In 1948, he received an honorary Doctor of Science degree from the Uni ...

in 1935; the type locality was Punta Chame in Panama, and the holotype was deposited in the

United States National Museum The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

as specimen USNM 47887. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

' commemorates the American

carcinologist A carcinologist is a scientist who studies crustaceans or is otherwise involved in carcinology Carcinology is a branch of zoology that consists of the study of crustaceans, a group of arthropods that includes lobsters, crayfish, shrimp, krill, ...

Mary J. Rathbun Mary Jane Rathbun (June 11, 1860 – April 4, 1943) was an American zoologist who specialized in crustaceans. She worked at the Smithsonian Institution from 1884 until her death. She described more than a thousand new species and subspecies and ...

Ecology

''Emerita rathbunae'' lives in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

, where it uses the swash for transportation and filter-feeding. In Ecuador, it is one of the most abundant animals to surf the swash, together with the

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

'' Olivella semistriata''. The two avoid competition since ''E. rathbunae'' prefers steeper beaches with coarser sediments and rougher swash than ''O. semistriata'', and positions itself lower in the swash than ''O. semistriata''. Based on comparisons with other ''Emerita'' species, ''E. rathbunae'' is thought to be a very capable swimmer, and to burrow rapidly into the sand.

Development

The

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

of ''E. rathbunae'' pass through a variable number of moults before reaching adulthood. While the majority of larvae pass through eight zoeal stages before reaching the megalopa, others may pass through seven or nine. This process lasts 64–96 days, during which time the larvae increase in length from around to around . They remain as megalopa larvae for 10–13 days, before moulting into the juvenile form.

References

{{Taxonbar, from=Q5370827 Hippoidea Crustaceans of the eastern Pacific Ocean Crustaceans described in 1935