TAXONOMY
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Pteriomorphia
Order: Pectinoida
Family: Pectinidae

Genus/species: Crassedoma giganteum

GENERAL CHARACTERISTICS: Giant Rock Scallops have coarsely ribbed shells called valves. The upper valve is usually scallop-shaped but the lower valve takes the shape of the substrate to which it’s attached. Between the valves, the margin of the orange mantle can be seen, with a row of tiny blue eyes and a sparse fringe of short tentacles

SIZE: up to a diameter of 15 centimetres (5.9 in) in the intertidal zone and 25 centimetres (9.8 in) in the subtidal zone.

DISTRIBUTION: Pacific coast California and Canada and south to Baja California and Mexico usually inside crevices and under boulders, or cemented to rock surfaces, Depth down to about 80 metres (260 ft).

DIET IN THE WILD: C. gigantea is a suspension feeder, filtering phytoplankton from water as it passes over the gills. The particles are moved by cilia along grooves to the mouth where edible matter is separated from sediment particles. The waste is incorporated into mucous balls which are removed from the mantle cavity periodically by a clapping of the valves.

REPRODUCTION: The sexes are separate in C. gigantea. The veliger larvae that develop from the eggs form part of the zooplankton for about 40 days before settling, undergoing metamorphosis and beginning to form a shell. Juveniles are free-living, are able to swim and can attach themselves temporarily to the substrate by byssus threads. 

PREDATORS: Sunflower starfish (Pycnopodia helianthoides) and purple sea star (Pisaster ochraceus).

REMARKS: The scallops eyes can’t see images as we can, but they allow the scallop to adjust to the brightness of light. This can be of benefit when it opens its protective shells to pump water over their gills filtering food thus exposing its soft body parts to predators. As a predator approaches at least some light will be blocked and the scallop closes it shells.

References

California Academy of Sciences Steinhart Aquarium Dr Charles Delbeek 2018

Ron’s flickr  https://www.flickr.com/photos/cas_docents/39884701811/in/album-72157675344287795/

iNaturalist  www.inaturalist.org/taxa/54526-Crassadoma-gigantea

Global species: www.globalspecies.org/ntaxa/913354

Reef.org www.reef.org/resources/galleries/invertebrate?page=1

Eyes. www.chuckkopczakphotography.com/blog/2015/11/13/the-eyes-…