File:American malacological bulletin (1988) (17968964730).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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REYNOLDS: SCAPHOPOD HEART 139
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Fig. 1. Longitudinal section through the perianal sinus (pa), kidney (n), and anterior portion of stomach (s) and pericardium (arrowheads) (ab, abdominal sinus; mc, mantle cavity; pc, pericardial cavity; r, rectum). Scale bar = 0.1 mm. Fig. 2. Oblique cross section of the perianal sinus (pa), showing traversing muscular trabeculae (arrowheads) (mc, mantle cavity; r, rectum). Scale bar = 40 ^m. Fig. 3. Muscle cells of the perianal sinus (sm) and the pericardium (pm). Note neural process adjacent to perianal sinus musculature (arrowhead) (h, haemocoel; pc, pericardial cavity; pe, pericardial epithelial cell). Scale bar = 1 /xrn. Fig. 4. Cytoplasmic extensions of a pericardial epithelial cell overlying a muscle cell of the perianal sinus (arrowheads, dense bodies; arrow, attachment plaque; g, glycogen granules; h, haemocoel; jsr, junctional sarcoplasmic reticulum; m, mitochondrion; pc, pericardial cavity; sr, sarcoplasmic reticulum; th, thick myofilaments). Scale bar = 0.5 nm. Fig. 5. Thick myofilaments of the smooth perianal sinus muscle cell. Note axial periodicity within the filaments. Scale bar = 0.2 fim. sinus, ventral to the stomach, and extends from the posterior end of the stomach to the kidneys and perianal sinus, to which it adheres anteriorly (Figs. 1, 6-8). The ventral pericardial epithelium is always in close contact with the body wall, while irregular infoldings of the dorsal pericardial wall project into the coelomic cavity. There is no myocardium or any type of endothelium within these foldings (Figs. 1, 7, 8); the only musculature adjacent to the pericardium is that of the body wall ventrally and perianal sinus anteriorly (Figs. 6, 7). A con- nection exists between the pericardial coelom and the right kidney (Fig. 9), although it was not found in all specimens. The pericardial wall is composed of three cell types: simple flat epithelium, interspersed with muscle cells, and modified in the region adjacent to the perianal sinus to in- clude podocytes. The arrangement and ultrastructure of epithelial and muscle cells is similar throughout the peri- cardium (Fig. 6). The epithelial cells (Fig. 10) typically possess a cell body with a small amount of cytoplasmic material sur- rounding the nucleus. The cell bodies extend into the pericar- dial cavity, with the continuous basal lamina lining the haemocoel. Thin cytoplasmic branches extend between cell bodies and contain one or a few isolated mitochondria in ad- dition to a- (15 nm) and 0- (37 nm) glycogen granules (Figs. 10-12). Desmosomes, with an intercellular distance of 9-15 nm, occur frequently where epithelial cell junctions appose the basal lamina (Fig. 11) but were not observed in areas where cytoplasmic extensions overlap adjoining muscle cells (Fig. 12). Adjoining plasmalemmae are not highly infolded and do not interdigitate (Fig. 12). The pericardial musculature is arranged as trabeculae which run in an entirely transverse direction, and are discon- tinuous in both anterior-posterior and lateral axes of the pericardium. The width of the trabeculae varies between 1 and 10 ftm (Figs. 13, 14). Muscle cells are interspersed be- tween the epithelial cells and typically underlie extensions of the epithelial cytoplasm (Figs. 12, 15-18). Adjoining plas- malemmae of the two cell types have an intercellular space of 7-15 nm within which no extracellular material has been observed (Figs. 12,15, 16,18). Desmosomes occur at cell junc- tions apposing either the basal lamina or coelomic space, and have an intercellular width of 9-15 nm (Fig. 16, 18). Both cell types are separated from the haemocoel by a continuous basal lamina, 18-40 nm thick (Figs. 12, 15-18). A thin layer of collagen fibrils, varying in thickness from 0.11-0.53 ^m, is often associated with the basal lamina (Fig. 15). Neural elements are found adjacent to the muscle cells (Fig. 17).

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