THE AMERICAN OYSTER CRASSOSTREA VIRGINICA GMELIN By PAUL S. GALTSOFF, Fishery Biologist BUREAU OF COMMERCIAL FISHERIES CHAPTER I TAXONOMY Page This broad characterization included a number Taxonomic characters _ 4 SheIL _ 4 of genera such as scallops, pen shells (Pinnidae), Anatomy _ 4 Sex and spawnlng _ limas (Limidae) and other mollusks which ob­ 4 Habitat _ 5 viously are not oysters. In the 10th edition of Larvll! shell (Prodlssoconch) _ 6 "Systema Naturae," Linnaeus (1758) wrote: The genera of living oysters _ 6 Genus 08trea _ 6 "Ostreae non orones, imprimis Pectines, ad Genus Cra8808trea _ 7 Genus Pycnodonte _ cardinem interne fulcis transversis numerosis 7 Bibliography _ 14 parallelis in utraque testa oppositis gaudentiquae probe distinguendae ab Areis polypleptoginglymis, The family Ostreidae consists of a large number cujus dentes numerosi alternatim intrant alterius of edibleand nonedible oysters. Their distribution sinus." Le., not all are oysters, in particular the is confined to a broad belt of coastal waters within scallops, which have many parallel ribs running the latitudes 64° N. and 44° S. With few excep­ crosswise inward toward the hinge on each shell tions oysters thrive in shallow water, their vertical on opposite sides; these should properly be dis­ distribution extending from a level approximately tinguished from Area polyleptoginglymis whose halfway between high and low tide levels to a many teeth alternately enter between the teeth depth of about 100 feet. Commercially exploited of the other side. oyster beds are rarely found below a depth of 40 In the same publication the European flat feet. oyster, Ostrea edulis, is described as follows: The· name "Ostrea" was given by Linnaeus "Vulgo Ostrea dictae edulis. O. testa semi­ (1758) to a number of mollusks which he described orbiculata membranis imbricatis undulatis: as follows: valvula altera plana integerrima." i.e., commonly "Ostrea. Animal Tethys, testa bivalvis in­ called edible oyster; shell semicircular, outer valve aequivalvis, subaurita. Cardo edentulus and with wavy grooves; the other small valve com­ fossula cava ovata, striisque lateralibus transversis. pletely flat. With a minor change Linnaeus' Vulva anusve nullus." The name Tethys (from diagnosis is repeated by Gmelin (1789). Greek mythology and also refers to the sea) Lamarck (1801) restricted the family Ostreidae applies to the type of marine animals, living either to the species of the genus Ostrea which was within the shells or naked, that Linnaeus listed characterized by him as follows: Adhering shell, under a general name "Vermes" which includes valves unequal, irregular, with divergent beaks worms, mollusks, echinoderms, and others. The which with age become very unequal; the upper translation of Linnaeus' diagnosis reads as follows: valve becomes misplaced. Hinge without teeth. Shell bivalve, unequal, almost ear-shaped. Hinge Ligament half internal, inserted in the cardinal toothless, depression concave and oval-shaped, lunule of the valves; the lunule of the lower with transverse lines on the sides. No vulva or valve and the beak grow with age and sometimes anus. reach great length. Great confusion in the usage of the generic NOTE.-Approved for publication April 24, 1964. name of living oysters resulted, however, from FISHERY BULLETIN: VOLUME 64, CHAPTER I 1 remotely resembles the curved beak of the Gryphaea. Oysters are frequently found so closely adhering to the substratum that their shells faithfully re­ produce the configurations and detailed structures of the objects upon which they rest. For instance, under the name of Ost1'ea tube1'culata, Lamarck (1819) described a shell from the Timor Sea (Netherland Indies) grown on a coral of the family Astraeidae; this particular shell repeated the tubercles and other structural elements of the coral upon which it was resting. Other speci­ mens of the same species, but grown on a smooth surface, were listed as different species. O. haliotidea of Australia, another Lamarckian species ! assumed a shape of the abalone shell to which it 6 was attached. Oysters adhering to the shells of Centimeters T1'ochus maculatus repeated the granular structure of this gastropod (Smith, 1878), while those grown FIGURE l.-Gryphaea arcuata, Jurassic fossil. Specimen No. 283 from the Museum of Comparative Zoology, on branches of mangrove trees usually formed a Harvard University. Dimensions: height 8.5 em., groove be,tween the folds of the shell facing the depth 3.5 em. branch while the same species attached to the trunk of the tree did not develop such structure Lamarck's (1801) allocation of extinct and recent (Gray, 1833). O. equestris found growing on species of oysters to the genus Gryphaea. Under navigation buoys (Galtsoff and Merrill, 1962) re­ this generic name, which was published with a peated the configurations of bolts and shells of diagnosis, Lamarck included nine nominal species, barnacles upon which they happened to attach some of which at the time of publication were themselves. "nomina nuda" since they lacked diagnosis, but The influence of other factors of the environ­ other species were validated by citation of biblio­ ment on the shape and sculpture of oyster shell graphical references (Hemming, 1951). Lamarck has been reported by many investigators who had not designated the type species, and a selec­ noticed that specimens growing in calm water on tion of "types" was made by Anton (1839), who flat surfaces have a tendency to acquire a round designated fossil Gryphaea a1'cuata (fig. 1) as type. shape and to have poorly developed umbones. On Dall (1898) and Anthony (1906) also selected G. soft bottom and overcrowded reefs the same species a1'cuata as type. A living species, G1'yphaea angu­ tend to form long and slender, laterally compressed lata, was included by Lamarck (1801) but without bodies with hooklike umbones. Lamy (1929) a diagnosis. observed that oysters attached to a pebble or shell Lamarck (1819) further confused the nomen­ and, therefore, slightly raised above the bottom, clature of the genus Ost1'ea when he again described had deep lower valves, more or less radially ribbed. the genus G1'yphaea. A longer list of species This type of structure, according to Lamy, offered included common oyster of Portugal and Medi­ greater resistance to dislodgment by currents or terranean, Gryphaea angulata, this time, however, wave action. with a diagnosis (fig. 2). It was assumed by Since Lamarck's inclusion of a living estuarine Children, Grey, Fisher, Tryon, Stoliczka, and species, G. angulata, in one genus with the fossil Sacco (quoted from Dall, 1898: 671-688) that Jurassic and Cretaceous Gryphaeas was not ac­ G. angulata is Lamarck's type species, an opinion ceptable to many biologists, the question was entirely without foundation. Anatomical and embryological studies have demonstrated that submitted for ruling by the International Commis­ G. angulata has no characteristics of the fossils sion on ZoologICal Nomenclature. The retention G1'yphaeidae. The species is simply another type of the name"Gryphaea" and the designation of G. of oyster similar to the American species (C. angulata as the type species of the genus Gryphaea vi1'ginica), with a slightly twisted beak which only was favored by the "majority" of European zool- 2 FISH AND WILDLIFE SERVICE 5 Cent imeters FIGURE 2.-(a) Crassostrea angulata, Arcachon, France. Dimensions: height 9 em., length 5 em. (b) C. virginica, Brownsville, Tex. Dimensions: height 8.5 em., length 4.5 em. Note similarity of the two forms. ogists (Ranson, 1948a) who requested the Interna­ with an indication for the recent species to which tional Commission tosuppress thename IIGryphaea" it is applicable until 1819). (Lamarck 1801) as applied to fossil species and to "This nominal species Gryphaea angulata La­ validate the name "Gryphaea" (Lamarck 1819) marck, 1819, is not the type species of any nominal which included the living oysters. The American genus, but the generic name Orassostrea Sacco, zoologists (Gunter, 1950) were in favor of retaining 1897, is available for use for that species by those the name "Gryphaea" for fossil forms. specialists who regard it as congeneric with Ostrea The findings of the International Commission, virginica Gmelin, (1790) (the type species of published as Opinion 338 on March 17, 1955, are as Crassostrea Sacco) and who do not refer both species follows: to the genus Ostrea Linnaeus, 1758." The names Gryphaea Lamarck, 1801, Cras­ Gryphaea Lamarck, 1801, is available for the sostrea Sacco, 1897, arcuata Lamarck, 1801 (Gry­ purposes of the Law of Priority and has as its type phaea) and angulata Lamarck, 1819 (Gryphaea) species the Mesozoic Fossil species G. arcuata were placed on the Official Lists of Generic Names Lamarck, 1801, by selection by Anton (1839), and Specific Names respectively and the nomen and not G. angulata Lamarck, 1801, which was nudum angulata Lamarck, 1801 (Grypnaea) was selected by Children in 1823, this latter name placed on the Official Index of Rejected and Invalid being a nomen nudum (not having been published Names in Zoology. TAXONOMY 3 TAXONOMIC CHARACTERS recognizing some species (0. (Alectryonia) mego­ According to the view shared today by all don, fig. 3) with valves reinforced by a number of specialists On pelecypod taxonomy, the genus prominences or folds (also called ribs, ridges, or Ostrea (in a broad sense), as characterized by flutings by various authors) which end in the Lamarck, comprises several groups of oysters of crenulations at the edge of the shell. In American the family Ostreidae sufficiently different to be oysters this character varies greatly depending on considered as separate genera or subgenera local conditions but is rather constant in O. (Lamarck, 1819; Thiele, 1935). There is, how­ equestris (Galtsoff and Merrill, 1962). ever, no general agreement about the validity The position of the muscle scar and its outline of various genera and speci~s. A uniform system differs in various species and, therefore, is used of classification of oysters is lacking, and for the as a taxonomic character.