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COCKLE

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Originally appearing in Volume V06, Page 627 of the 1911 Encyclopedia Britannica.
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COCKLE , in See also:

zoology, a mollusc (Cardium) of the class See also:Lamellibranchia (q.v.). A very large number of See also:species of Cardium have been distinguished by conchologists. Besides the See also:common species Cardium edule, two others occur in See also:Britain, but are not sufficiently common to be of commercial importance. One of these is C. echinatum, which is larger than the common species, reaching 3 in. in See also:diameter, and distinguished by the presence of spines along the ribs of the See also:shell. The other is C. norvegicum, which is also somewhat larger than C. edule, is longer dorsoventrally than broad, and is only faintly ribbed. The two valves of the shell of the common cockle are similar to each other, and somewhat circular in outline. The See also:beak or umbo of each See also:valve is prominent and rounded, and a number of See also:sharp ridges and furrows radiate from the See also:apex to the See also:free edge of the shell, which is crenated. The See also:ligament is See also:external, and the See also:hinge carries See also:cardinal See also:teeth in each valve. The interior of the shell is remarkable for the See also:absence of pearly lustre on its interior See also:surface. The See also:colour externally is reddish or yellowish. The pallial See also:line, which is the line of See also:attachment of the See also:mantle parallel to the edge of the shell, is not indented by a sinus at the posterior end. In the entire See also:animal the posterior end projects slightly more than the anterior from the region of the umbones.

The animal possesses two nearly equal adductor muscles. The edges of the mantle are See also:

united posteriorly except at the anal and branchial apertures, which are placed at the ends of two very See also:short siphons or tubular prolongations of the mantle; the siphons See also:bear a number of short tentacles, and many of these are furnished with See also:eye-spots. The See also:foot is very large and powerful; it can be protruded from the anterior See also:aperture between the mantle edges, and its See also:outer See also:part is See also:bent sharply forwards and terminates in a point. By means of this See also:muscular foot the cockle burrows rapidly in the muddy See also:sand of the See also:sea-See also:shore, and it can also when it is not buried perform considerable leaps by suddenly bending the foot. The foot has a byssus gland on its posterior surface. On either See also:side of the See also:body between the mantle and the foot are two See also:flat gills each composed of two lamellae. Cardium belongs to the See also:order of Lamellibranchia in which the gills See also:present the maximum of complexity, the See also:original See also:vertical filaments of which they are composed being united by interfilamentar and interlamellar junctions. In other respects the See also:anatomy of the cockle presents no important See also:differences from that of a typical Lamellibranch. The sexes are distinct, and the generative opening is on the side of the body above the edge of the inner lamella of the inner gill. The eggs are See also:minute, and pass out into the sea-See also:water through the dorsal or exhalent See also:siphon. The breeding See also:season is See also:April, May and See also:June. The larva for a See also:time swims freely in the sea-water, having a circlet of See also:cilia See also:round the body in front of the mouth, forming the velum.

The shell is See also:

developed on the dorsal surface behind the velum, the foot on the opposite or ventral surface behind the mouth. After a few days, when the mantle bearing the shell valves has developed so much as to enclose the whole body, the See also:young cockle sinks to the bottom and commences to follow the habits of the adult, The usual See also:size of the cockle in its shell is from 1 to 2 in. in breadth. The common cockle is regularly used as See also:food by the poorer classes. It occurs in abundance on sandy shores in all estuaries. At the mouth of the See also:Thames the gathering of cockles forms a considerable See also:industry, especially at See also:Leigh. On the See also:coast of See also:Lancashire also the See also:fishery, if it may be so called, is of consider-able importance. The cockles are gathered by the See also:simple See also:process of raking them from the sand, and they are usually boiled and extracted from their shells before being sent to See also:market. The cockle is liable to the same suspicion as the See also:oyster of conveying the contamination of typhoid See also:fever where the shores are polluted, but as it is boiled before being eaten it is probably less dangerous. (J. T.

End of Article: COCKLE

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