File:American malacological bulletin (1986) (18152691252).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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66 AMER. MALAC. BULL. 4(1) (1986)
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1982 1983 1984 Fig. 3. Percent of C. fluminea examined from ANO intake bays (Arkansas River) near Russellville, Arkansas, having embryos in the inner gills, in relation to water temperature. tissue dissections of the visceral mass. (3) Finally, AP&L per- sonnel have noted that the greatest likelihood of a "clam clog" at ANO in Russellville, has regularly been during the fall. FERTILIZATION Earlier studies (Kraemer 1978, 1979, 1984; Kennedy ef a/., in press; Kraemer, ef a/., in press) had adduced that C. fluminea carries out both self fertilization and cross fer- tilization. Cross fertilization apparently occurs when spheres of mature sperm make their way out of the gonopores, which are paired and located on either side of the posterior, dor- solateral aspect of the visceral mass (Kraemer, 1978), where the gonopores open into the subrabranchial cavity. Sperm then may be carried to the exterior via the excurrent siphon of the clam and through the water to the siphons of neighbor- ing clams. In this study we repeatedly observed that sperm cells separate from the spheres in the dilute external environ- ment. Sperm thus appear to be transmitted as individual cells. A similar phenomenon regarding the separation of sperm from sperm "morulae" has recently been analyzed in the polychaete, Arenicola sp. (Bentley, 1985). Self fertilization apparently occurs late in the fall reproductive pulse (late September and October in Arkan- sas) and involves regions of the "follicular ganglia" (Kraemer 1978, 1980, 1984, in press) in areas of contiguity between oogenic and spermatogenic follicles. Serial sections reveal the presence of many embryos there, most being in blastula or gastrula stages. Identification of intrafollicular embryos by means of fresh tissue dissection (as noted in Materials & Methods) showed these also to be usually blastula or gastrula stages. In this study it was possible to visualize the jelly coat of the oocyte with SEM, along with the yolky cytoplasm and conspicuous nucleus (Fig. 4c,d). Relative size of the oocyte and mature, biflagellate sperm are shown in Fig. 4c,d, though the actual process of sperm penetration was not encountered in our freeze-cracked, SEM preparations. It is possible to iden- tify fertilized eggs in fresh tissue dissections, as they manifest (1) a clearly visible depression in the egg cytoplams, the ap- parent penetration site (Fig. 5a); and (2) a fertilization mem- brane and evident loss of the oocyte's gelatinous coat (Fig. 5).

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