File:American malacological bulletin (1988) (17968974720).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (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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V Fig. 8. Longitudinal section through the pericardium (pc), stomach (s), perianal sinus (pa) and kidney (n) (arrowheads, anterior and dorsal pericardial walls; ab, abdominal sinus; dd, digestive diverticulum; i, intestine; mc, mantle cavity). Scale bar = 0.15 mm. Fig. 9. Longitudinal section showing connection between the pericardial cavity (pc) and the right kidney (n) (dd, digestive diverticulum; mc, mantle cavity; s, stomach). Scale bar = 50 nm. Fig. 10. Pericardial epithelial cell (arrow, basal lamina; h, haemocoel; m, mitochondrion; n, kidney; pc, pericardial cavity). Scale bar = 2.5 /im. Fig. 11. Cytoplasmic extensions of the pericardial epithelium (arrowhead, desmosome; h, haemocoel; pc, pericardial cavity). Scale bar = 0.3 ^m. Fig. 12. Epithelial (pe) and muscle cells (pm) of the pericardium (arrowhead, basal lamina; arrow, myofilaments; h, haemocoel; pc, pericardial cavity; sr, sarcoplasmic reticulum). Scale bar = 0.6 ^m. in the heart, and cardiac refilling is maintained by a volume- compensating mechanism as originally proposed by Ramsay (1952) and Krijgsman and Divaris (1955), and reviewed by Jones (1983). The pericardium is drained by one or two renopericardial canals, which connect the lumina of the pericardium with those of the kidneys (Martin, 1983). At the cellular level, the molluscan heart consists of an epicardium, which rests on a basal lamina, and an inner loose myocardium; an endothelium is lacking (Narain, 1976; ©kland, 1980; Jones, 1983) except in cephalopods, where it is incomplete (Jensen and Tj©nneland, 1977). While in some cases the epicardial cells possess microvilli and can also have a secretory role (Kling and Schipp, 1987), the ventricular epicardium generally consists of a continuous, simple epithelium. Podocytes are usually concentrated within the auricular epicardium, and are characterized by the presence of numerous thin cytoplasmic extensions termed pedicels, which are aligned in a parallel array over the continuous basal lamina, between the haemocoel and coelomic spaces (Andrews, 1976; Pirie and George, 1979; Okland, 1980). The gaps between the pedicels create fenestrations in the epithelium or ultrafiltration slits; the basal lamina separates the haemocoel from pericardial coelom, and acts as the func- tional filter (Andrews, 1981; Morse, 1987). In many bivalves, gastropods and cephalopods the ultrafiltration slits are bridged by slit diaphragms (Boer and Sminia, 1976; Andrews, 1979; Schipp and Hevert, 1981; Meyhdfer er a/., 1985), although these have not been found in the podocytes of chitons (©kland, 1980). Portions of the auricular epicardium or pericardial epithelium are elaborated in many species, par- ticularly in bivalves, to form pericardial glands (White, 1942), within which extensive areas of podocytes have been found (Meyhofer ef a/., 1985). A similar development of the haemocoel-pericardial interface is seen in the branchial heart appendages of coleoids and the pericardial appendages of nautiloid cephalopods (Fiedler and Schipp, 1987). The molluscan pericardium consists primarily of simple epithelial cells, although there have been few detailed ultrastructural studies. The polyplacophoran pericardial epithelium is con- tinuous with, while differing from, the ventricular and auricular epicardium (©kland, 1980); it also possesses muscle cells and is pulsatile (Greenberg, 1962; ©kland, 1981). INTERPRETATIONS OF SCAPHOPOD CIRCULATORY STRUCTURES TO DATE Two structures have been proposed as representing the scaphopod heart: (i) the perianal sinus, which has been described as having morphological similarities to (Lacaze-

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