File:American malacological bulletin (1988) (18153159182).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 143 Duthiers, 1857) and homology with (Fol, 1889) the bivalve ven- tricle; and (ii) the dorsal infolding of the pericardium, ventral to the stomach, described by Plate (1891, 1892), Boissevain (1904), and Distaso (1905). Lacaze-Duthiers (1857) did not discuss the relationship between the perianal sinus and molluscan heart in any detail. Fol (1889), however, based their homology on structural similarities, describing the posi- tion of the sinus in relation to the rectum, the musculature and rhythmic contractions of the sinus, and an endothelium which Plate (1892) and Boissevain (1904) later refuted. Lacaze-Duthiers (1857) placed the major responsibility for movement of the blood with the large pedal sinus, while Fol (1889) agreed that the perianal sinus makes little contribu- tion to circulation. The studies by Plate (1891, 1892), which were con- firmed by Boissevain (1904) and Distaso (1905), described a contractile vessel ventral to the stomach, surrounded by the pericardial coelom. Plate (1892) stated that the heart is ex- traordinarily simple, with no chambers or vessels, and lacks a strong development of musculature. He found that the pericardial and heart walls did not differ histologically, and were composed of epithelial cells with very thin, parallel and regularly arranged fibres. While Plate (1892) suggested that these could be muscle fibres, he concluded that this struc- ture could not act as a center of propulsion for the circulatory system. CIRCULATORY STRUCTURES IN DENTALIUM RECTIUS In Dentalium rectius, there is no evidence of the ultrastructural features associated with the typical molluscan heart (i.e. a myocardium with an associated epicardium) in a position ventral to the stomach and enclosed by the peri-
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Fig. 21. Junction of pericardial muscle cells (m, mitochondrion; pc, pericardial cavity; th, thick myofilaments). Scale bar = 1 ^m. Fig. 22. Podocytes in the pericardium. Note fenestrations in the pericardial epithelium apposed by basal lamina (arrowheads) (nu, nucleus; pc, pericar- dial cavity). Scale bar = 1 /xm. Fig. 23. View of perianal sinus muscle cells (sm) and pericardium. Note the highly infolded cytoplasmic exten- sions of the pericardium overlying the perianal sinus musculature, and the fenestrations apposed by basal lamina (arrowheads) (h, haemocoel; pc, pericardial cavity). Scale bar = 1 //m. Fig. 24. Muscle cell of perianal sinus (sm) and fenestrations (arrowheads) in the overlying pericar- dium (g, glycogen granules; th, thick myofilaments). Scale bar = 0.7 fim.

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