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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72 AMER. MALAC. BULL. 4(1) (1986)
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Fig. 9 a-d. Photomicrographs of Corbicula fluminea during transition from late pediveliger to early juvenile stages, (a) Late pediveliger shown "casting off" the velum, after repeated adduction of valves was induced by pressure of coverslip on the embryo. Horizontal field width = 570 iim. (b) Late pediveliger shown spontaneously casting off velum. Micrograph from videotape. Horizontal field width = 250 fim. (c) Early juvenile, immediately following casting off of velum, showing "abscission" site from which velum was recently detached. Micrograph from videotape. Horizontal field width = 260 fim. (d) Photomicrograph from videotape of young juvenile showing fecal strand emerging from be- tween distended mantle lobes. Although siphons have not yet formed, posterior region of gut has differentiated and is functioning. Horizontal field width = 230 ^m. AS, abscission site; F, foot; FS, fecal strand; LS, larval shell; M, mantle; V, velum. What has not been appreciated until the present study, is the fact that the statocysts are large (approaching adult size at 15 /tm) and well differentiated in the juvenile clams. With videomicroscopy the statocysts can be observed dur- ing foot movements. In the early juvenile, the statocysts are located in the distal half of the foot, (Fig. 9c) and in the later juvenile the statocysts are found in the proximal third of the foot (Fig. 10b,c,d). It is apparent that the change in position of the statocysts is due to progressive lengthening and dif- ferentiation of the foot. High-power videomicroscopy allowed us to note that the statoliths in both statocysts are also dif- ferentiated and move continuously as the juvenile clam's foot moves. The statocysts of C. fluminea are much implicated in the movements of the juvenile foot. In the course of the present study, SEM micrographs of the foot of the juvenile clam revealed a series of 10-12 membranous laminae which comprise the outer surface of the foot (Kraemer, 1984). Examination of serial sections had shown the existence of a "segmental" array of horizontal strands of connective tissue and muscle fibers repeated in the interior of the foot from the distal to the proximal portion of the foot. Videomicroscopy enabled us to see the arrange- ment of the horizontal "ligaments" in the foot and to ap- preciate the structural/functional basis for the very active, telescoping movements of the juvenile foot. The locomotor behavior of the juvenile clam does not resemble that of the adult. The juvenile readily swings its foot forward or backward, from side to side in a circular movement, or uses the foot to somersault the rest of its body. The shell valves gape wide- ly, and along with the pallium assist the juvenile clam in cling-

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