Armases

Abele, 1992

square-back American marsh crabs

Armases is a of sesarmid crabs comprising approximately 13 described distributed across tropical and subtropical coastal regions of the Americas. These semi-terrestrial crabs inhabit salt marshes, mangroves, and estuarine environments, with some species exhibiting notable movement between marine and terrestrial . Several species have been extensively studied for their larval development, metabolic , and role in energy transfer. The genus includes both species with larval export strategies to continental shelves and those breeding in supratidal rock pools.

Armases by (c) Evan M. Raskin, some rights reserved (CC BY), uploaded by Evan M. Raskin. Used under a CC-BY license.

Armases cinereum QA-Co 10-03-11 (24607687160) by Smithsonian Environmental Research Center. Used under a CC BY 2.0 license.

Armases cinereum P1010755a by
xpda. Used under a CC BY-SA 4.0 license.

Pronunciation

How to pronounce Armases: /ˈɑːr.mə.siːz/

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Identification

Armases are distinguished from other sesarmid by their square-backed shape, giving rise to the "square-back marsh crabs." Species-level identification requires examination of carapace width, male , and coloration patterns. Armases angustipes and A. miersii are particularly difficult to distinguish morphologically and have historically been misidentified; genetic analysis may be required for definitive identification where ranges approach potential overlap.

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Habitat

Salt marshes, mangroves, and estuarine creeks; semi-terrestrial at the marine-terrestrial . Some inhabit supratidal rock pools. of at least one species (A. rubripes) occur in oligohaline Amazonian creeks with floodplain vegetation, influenced by mesotides.

Distribution

Tropical and subtropical zones of the Americas. A. cinereum ranges from Chesapeake Bay to Florida and throughout the Gulf of Mexico to Veracruz, Mexico. A. rubripes occurs along the Brazilian coast and Amazon region. A. angustipes is primarily South ; museum specimens from the Bahamas previously attributed to this have been re-identified as A. miersii, suggesting A. angustipes may be restricted to southern distributions without geographic overlap with A. miersii.

Seasonality

Reproductive activity varies by and region. A. rubripes shows peak larval abundance during the Amazon rainy season (January) with present quarterly. A. angustipes exhibits ovigerous females primarily in summer months. A. cinereum shows year-round activity with temperature-dependent metabolic rates.

Life Cycle

Four zoeal larval stages followed by a megalopa stage. At least one (A. rubripes) exhibits larval exportation to the continental shelf, with only zoea I present in oligohaline nursery . A. miersii breeds in supratidal rock pools with facultative lecithotrophic larval stages. First sexual maturity occurs at approximately 6.5 mm width in male A. rubripes and 8.1 mm in females.

Behavior

Highly mobile with bi-directional movement between marsh and forest in some . A. cinereum females feed preferentially in salt marshes and move to upland forest, while males prefer forest habitat with more restricted ranges. Limb loss and are common. Larval exportation to marine environments represents a strategy for some species.

Ecological Role

Mediates energy fluxes between and along marine-terrestrial . Acts as a potential for spatial subsidies of energy from salt marshes to upland forests, though high metabolic expenditures limit energy transfer. Serves as a bioindicator of water quality; larval abundance and distribution are sensitive to anthropogenic , nitrogenous compounds, and coliform concentrations.

Similar Taxa

SesarmaSimilar semi-terrestrial sesarmid crabs; Armases distinguished by square-backed and specific characteristics
AratusAnother sesarmid inhabiting mangroves; Armases typically occupy lower intertidal and marsh rather than mangrove roots