IUCN threat status:

Not evaluated

Comprehensive Description

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Biology/Natural History: A number of crabs may be found inside a clam but usually only one pair is mature. The presence of the adults seems to hinder the maturation of the juveniles. The small male crabs move around but the larger females remain sheltered by a fringe of tissue, the visceral skirt, attached to the clam's visceral mass. They scrape plankton from the clam's feeding mucus from this fringe. They cause slight damage to the host. Alternate hosts include the clams Tresus nuttallii, Macoma nasuta, Mya arenaria, Saxidomus gigantea, Clinocardium nuttallii, Siliqua patula, and Protothaca staminea; the mantle folds of the sea hare Aplysia vaccaria (in California), the atrial cavity of the tunicate Styela gibbsii, and in the cloaca of the sea cucumbers Caudina arenata, C. arenicola, and Cucumaria piperata. In Puget Sound adults seem to only be found in Tresus capax. In Washington, some females with eggs can be found year-round, and most raise two broods per year. A female usually carries 7000-8000 eggs. Breeding is interrupted when the females molt, from late August to October. Larvae are planktonic for 47 days, then seek a clam host. These crabs have a terminal molt (after 14 postlarval instars for the male). Females are large enough to lay eggs when they reach a carapace width of 12.8 to 14 mm (15-16 instars) but continue to grow to 19.7 mm (23-24 instars).

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© Rosario Beach Marine Laboratory

Source: Invertebrates of the Salish Sea

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