Northern Quahog
Mercenaria mercenaria
Summary 2
The hard clam (Mercenaria mercenaria), also known as a Round Clam, or Hard-shell (or Hard-shelled) Clam, is an edible marine bivalve mollusk native to the eastern shores of North America, from Prince Edward Island to the Yucatán Peninsula. It is one of many unrelated edible bivalves which in the United States are frequently referred to simply as clams, as in the expression "clam digging".
Distribution 3
Newfoundland to Florida and Texas
Physical description 4
Mercenaria mercenaria has a fairly large and thick shell with uneven, elevated hinges on the anterior (Mercenaria mercenaria 2000). Both shell halves are approximately even in size and sub ovate, or triangular in shape (Stewart 1996). The shell is increased by a daily layering of aragonite secreted by the outermost fold of the organism, giving it numerous concentric lines that are closely space near the margins of the shell and widely spaced at the umboes (deMenocal 2000, Mercenaria mercenaria 2000). Its shell is a composition of proteins and calcium carbonate (Plourde 2001, Brown 1995). The shell is joined at a hinge called the umbo and is held closed by two pairs of adductor muscles located on each side of the shell (Plourde 2001). The clam opens its shell by relaxing the adductor muscles and contracting a pair of ligaments located on each side of the umbo (Plourde 2001). Mercenaria mercenaria contain three well-developed teeth located on the edge of the shell, which serve to enhance its tightness when closed (Stewart 1996). The external color is dirty white or gray, while the interior is usually white with distinct violet areas near the umbo. The clam contains a foot, which allows it to burrow into the sand (Plourde 2001). The clam also contains a set of long siphons, which stretch from the clam's mantle, the membranous sac that contains the internal organs and constitutes the body of the clam, to the surrounding medium outside of the shell (Plourde 2001). It uses these siphons for respiration and gathering food. Mercenaria mercenaria are sub classified by length. Chowders are the biggest measuring up to 3 inches in width, Cherrystones are 2 to 3 inches, Top Necks are 2 inches in width, and Little Necks are the smallest measuring 1 to 2 1/3 inches (International Seafood).
Look alikes 5
Similar to Mercenaria campechiensis. Mercenaria mercenaria is distinguishable by a central smooth region on the exterior of the valves, with stronger ribs anteriorly and posteriorly; whereas, Mercenaria campechiensis can be distinguished by ribs that become more dense and fine as the animal grows.
Similar to Pitar morrhuanus. Mercenaria mercenaria can be distinguished by its lack of lateral teeth and the presence of a central smooth region on the exterior of its valves.
Reproduction 6
When the water temperatures approach 23°C (73°F), and other environmental cues such as pH change, spawning commences (Britannica 2000, Stewart 1996). Some species have adapted to spawn at temperatures ranging from 4°C and lower (Mitchell 2001). The male clam discharges sperm into the water, which stimulates the female to release eggs (Stewart 1996). Because fertilization is random, high densities of spawning clams increase the probability of success (Cool 1998). Due to favorable conditions, spawning is most likely to occur during neap tides (Stewart 1996). During the first 12 to 14 hours, the fertilized eggs turn into trochophore larvae (Stewart 1996). In this form, they are cylindrical with tiny cilia, which allow them to swim about (Stewart 1996). During this period they feed on diatoms, microscopic algae that are encased in silica shells (Stewart 1996). By the end of the first day, the trochophore larvae transform into veliger larvae, which contain tiny lobes that may be used as paddles (Stewart 1996). During the next six to ten days, the body organs, shell and foot begin to form (Stewart 1996). They then shed their lobes and the newly developed foot secretes byssal threads that anchor the larvae to rocks, seaweed, or other sediment deposits (Plourde 2001, Stewart 1996). They will then secrete their shell, which begins to calcify between 8- 29°C, and detach the byssal threads, thus becoming adult clams (deMenocal 2000). During their free floating period they are dispersed by currents and preyed upon by other animals such as crabs. Approximately 10% of all veliger larvae reach the adult stage (Stewart 1996). Temperatures that vary below 80°C may reduce the growth stages dramatically (Mercenaria mercenaria 2000).
Link to Access Genomic Data 7
http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=6596&lvl=0
Sources and Credits
- (c) Casey Dunn, some rights reserved (CC BY-NC-SA), http://www.flickr.com/photos/12455333@N00/6195860344
- Adapted by matbio from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Mercenaria_mercenaria
- (c) WoRMS for SMEBD, some rights reserved (CC BY), http://eol.org/data_objects/29749207
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/18657991
- (c) Anderson, Katherine, some rights reserved (CC BY-NC), http://eol.org/data_objects/17784601
- Adapted by matbio from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/18657992
- (c) Emily Rose Sharkey, all rights reserved
