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Biology/Natural History: Very common in waters near Rosario. Often attach to the bottom by a few byssal threads. Nearly always lie with the left valve upward. Their left valve is usually more brightly colored than is the right valve. Are almost always covered by the encrusting sponge Myxilla incrustans (orange or yellow); less often by the brown or purple sponge Mycale adherens. These two sponges are found only on scallops. The symbiosis is likely mutualistic. If one of the major predators of the scallop, Evasterias troschelii, encounters the scallop (and the scallop does not swim away) it often turns away if it touches the sponge; likely in response to some secretion or to the spicules from the sponge. The sponge also appears to make it more difficult for the seastar's tube feet to adhere to the scallop. If the sponge is removed from the scallop and the scallop is prevented from swimming, it is readily captured by the seastar. The scallop will also swim from predators of the sponge, such as Archidoris spp, so the sponge is benefited as well. The swimming scallop may also help carry the sponge into areas with clean water and good currents, nd help prevent fouling of the sponge. Chlamys hastata is sometimes parasitized by the ectoparasitic Clam Sucker snail Odostomia columbiana. The foot is highly reduced and there are no siphons. The edge of the mantle is lined with small tentacles and several hundred beautiful blue eyes. These eyes can detect light and dark but cannot form an image. Filter feeds about 4 liters of water per gram per hour. Several seastars are predators of this species, including Pycnopodia helianthoides and Crossaster papposus. The scallops have a well-developed escape response of clapping the valves together like a pair of false teeth and swimming away by jet propulsion (contrary to what you might expect, the jet exits the dorsal side of the scallop, near the hinge). Click here for an .MPG file of the escape. Sexes are separate. The ovary is orange, testes are white. Veligers form about 50 h after fertilization. Form annual growth rings in January or February, live about 6 years in southern BC.


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© Rosario Beach Marine Laboratory

Source: Invertebrates of the Salish Sea

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