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The Anatomy of the Pelecypod Family Arcidae

Harold Heath
Transactions of the American Philosophical Society
Vol. 31, No. 5 (Aug., 1941), pp. 287-319
DOI: 10.2307/1005609
Stable URL: http://www.jstor.org/stable/1005609
Page Count: 56
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The Anatomy of the Pelecypod Family Arcidae
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Abstract

The ancient and geologically important family Arcidae is estimated to comprise upwards of eleven hundred species and subspecies. The greater number of these are in a fossil state, and obviously have been classified on the basis of shell characters. The same is true of many living species, and where anatomical studies have been made they usually were limited to some definite organ or system. While such a procedure results in supplying the morphologist with important data, it may lead to faulty conclusions on the part of the systematist. In the present work, for example, there are two types of individuals with identical shells and declared to be of the same species, whereas their anatomy proves them to be distinct. Furthermore, there are subspecies where the shells are unlike, while the internal organization would scarcely warrant subspecific rank. And again there are genera where a definite organ or system is of distinct diagnostic value; in other genera it is of doubtful worth. Under such circumstances it is apparent that comparisons must rest upon the entire organization of each species rather than upon one or a few selected elements. In the present study the anatomy of thirty-two species and subspecies has been described and figured in more or less detail. No attempt has been made to modify the existing scheme of classification beyond pointing out in the final paragraphs where certain changes appear to be in order. It may be added that the relatively wide range of differences between species of certain genera suggest further revisions, but the importance of these variations can be determined only after a study has been made of a greater number of additional species.

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