Dissodactylus

Smith, 1870

pea crab

Species Guides

1

Dissodactylus is a of pea crabs in the Pinnotheridae, comprising at least 20 described . Species in this genus are obligate ectosymbionts of echinoid , primarily sand dollars. The genus shows geographic variation in larval development: Pacific species have four zoeal stages, while Atlantic species have three. Several species have been studied for their host-finding , which rely on chemical cues to locate specific echinoid hosts.

Dissodactylus by (c) caymanmatt, some rights reserved (CC BY), uploaded by caymanmatt. Used under a CC-BY license.

Pronunciation

How to pronounce Dissodactylus: /ˌdɪs.oʊˈdæk.tɪ.ləs/

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Identification

Small-bodied crabs with reduced width, typically under 8 mm in . Distinguished from the related Clypeasterophilus by adult morphological features, particularly palp size: Dissodactylus possess "large-palped" versus the "small-palped" condition in Clypeasterophilus. Larval stages of Pacific species (D. xantusi, D. lockingtoni, D. nitidus) are morphometrically and meristically similar, requiring examination of spine length on the carapace and chromatophore patterns for identification.

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Habitat

Marine benthic environments, specifically shallow sand bottoms in the infralittoral zone. Occurs exclusively in association with echinoid , living as ectosymbionts on the external surfaces or within the body cavity of sand dollars and other irregular echinoids.

Distribution

Widespread in coastal marine waters of the Americas. Pacific occur from California to tropical eastern Pacific, associated with including Encope grandis, E. californica, E. micropora, and Mellita longifissa. Atlantic species occur along the eastern coasts of North and South America, including the southeastern Brazilian coast.

Seasonality

Recruitment occurs year-round in some , with peak recruitment documented in March for D. crinitichelis in Brazil. Breeding period extends across multiple months with ovigerous females present in population from August through July.

Host Associations

  • Encope emarginata - ectosymbiont for D. crinitichelis
  • Encope grandis - ectosymbiont for D. xantusi, D. lockingtoni, D. nitidus
  • Encope californica - ectosymbiont for D. xantusi, D. lockingtoni, D. nitidus
  • Encope micropora - ectosymbiont for D. xantusi, D. lockingtoni, D. nitidus
  • Mellita longifissa - ectosymbiont for D. xantusi, D. lockingtoni, D. nitidus
  • Mellita quinquiesperforata - ectosymbiont for D. mellitae
  • Meoma ventricosa - ectosymbiont for D. primitivus

Life Cycle

Development includes four zoeal stages and a megalopa stage in Pacific (D. xantusi, D. lockingtoni, D. nitidus), with total larval duration of approximately 15 days from hatching to megalopa in D. xantusi. Atlantic species have three zoeal stages. Complete to crab occurs after settlement on .

Behavior

Uses chemical stimuli to navigate toward and locate specific echinoid . Host-finding has been demonstrated in D. primitivus and D. crinitichelis, with crabs responding to waterborne cues from host Meoma ventricosa and chemical signals. Laboratory-reared larvae show -specific settlement preferences.

Ecological Role

Obligate ectosymbiont of irregular echinoids, forming intimate associations with sand dollar . structure suggests spatial segregation by size class within host populations. Potential competitive interactions with other pinnotherid documented where host ranges overlap.

Similar Taxa

  • ClypeasterophilusFormerly included within Dissodactylus; distinguished by "small-palped" versus "large-palped" condition in Dissodactylus, and by larval characteristics. Recently separated based on morphological and developmental differences.

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