Description: English: Senilia senilis Linnaeus, 1758 - senile ark clam (public display, Bailey-Matthews Shell Museum, Sanibel Island, Florida, USA) Bivalves are bilaterally symmetrical molluscs having two calcareous, asymmetrical shells (valves) - they include the clams, oysters, and scallops. In most bivalves, the two shells are mirror images of each other (the major exception is the oysters). They occur in marine, estuarine, and freshwater environments. Bivalves are also known as pelecypods and lamellibranchiates. Bivalves are sessile, benthic organisms - they occur on or below substrates. Most of them are filter-feeders, using siphons to bring in water, filter the water for tiny particles of food, then expel the used water. The majority of bivalves are infaunal - they burrow into unlithified sediments. In hard substrate environments, some forms make borings, in which the bivalve lives. Some groups are hard substrate encrusters, using a mineral cement to attach to rocks, shells, or wood. The fossil record of bivalves is Cambrian to Recent. They are especially common in the post-Paleozoic fossil record. The senile ark clam shown above is part of the West African Province: "The warms waters of the West African coast of the Atlantic possess very unique species, especially in the volute, murex, and margin shell families. The region extends from Morocco to Angola with habitats varying from muddy sand flats to stretches of black basalt rock. People in this area use mollusks extensively for food." [info. from museum signage] Classification: Animalia, Mollusca, Bivalvia, Pteriomorphia, Arcoida, Arcidae Locality: unrecorded/undisclosed/unspecified. Date: 3 January 2016, 17:31:38. Source:
https://www.flickr.com/photos/47445767@N05/24431841463/. Author: James St. John.
