Kingdom:
AnimaliaPhylum: Mollusca
Class: Bivalvia
Order: Osteroida
This is most likely a rock scallop (Crassadoma gigantea), although it is unusual to find them lying loose like this at this size. They are free living until about 2 inches, when they attach to the substratum [1]. They then cement their right valve to something and they grow to fit the contours of what they attached to.
You can see the concentric rings of the gills on the inside, which they use to filter feed, and the small black dots on the outer ring of the orange mantle are the eyes. Of all of the molluscs, scallops have the most developed eye structure [2]. Most other molluscs posses pigment cups or eye spots. The scallop's eye is composed of a lens, two retinas (the distal retina, which faces towards the light, and the proximal retina, which faces away from the light source), and a reflective tapetum layer, which often gives scallop eyes a blue sheen. These eyes are most often used to detect changes in light levels, allowing free living scallops to escape when a potential predator passes.
3 comments:
grow to fit the contours of what they attached to
That could prove problematic if they don't settle in the right place! Are their settlement cues known?
Yes and no. There is an interesting article by Culver et al. (2005 aquaculture), which postulates that there is a size requirement and a suitable surface requirement. They say that they can re-cement themselves if they are disturbed, and can live free if no suitable surface is present.
I guess it's not like settlement from a larval perspective, although other scallops which settle out of the plankton as larvae respond to excess potassium.
I had no idea scallops had eyes - that's my useful fact for the day - thanks Brine Queen!
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