File:American malacological bulletin (1988) (18129720426).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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Fig. 10. Semischematic representation of radular sac cross-section shown in figure 9 (er, epithelium of radular membrane; m, membranes bounding left and right groups of radula secretory cells; mu, mus- cle; od, odontoblasts; t,, early tooth, or perhaps denticle, not yet stain- ing with haemotoxylin; t2, older tooth stained by haemotoxylin). Scale bar = 35 nm. only a few rows of single teeth, usually 6 or fewer. Its monostichous form appears to be the result of reduction and fusion of a distichous radula, with two of its paired denticles fused at tip and base. In the Prochaetodermatidae, the radula has evolved into a rasping structure with a unipartite radular membrane and a central tooth, or plate (Fig. 12) (Scheltema, 1981,1985). There are no distinctive radula characteristics, syn- apomorphies, held in common or uniquely by the Aplacophora and Polyplacophora, the latter with rows of usually 17 teeth on a unipartite radular membrane. ONTOGENY OF GASTROPOD AND CHITON RADULAE Vestiges of an original distichous molluscan radula ex- ist in the ontogenetic development of the chiton, pulmonate, opisthobranch, and prosobranch radula. The details of the developing chiton radula are treated by Eernisse and Kerth (1987) and Kerth (this symposium). The radula starts as rarely one to usually three pairs of lateral teeth on a unipartite radular membrane with a central tooth added later. In the ontogenetic development in five families and seven species of pulmonates, the radula begins as a distichous structure with two longitudinal rows of lateral teeth on a unipartite radular mem- brane; further laterals are then added, and finally a central tooth, which originally may be paired, is secreted thereby uniting the cross-rows (Kerth, 1979). Pruvot-Fol (1926) figured the earliest radular teeth of the opisthobranch Polycera,
Text Appearing After Image:
Fig. 11. Monostichous aplacophoran radula of an undescribed species of Atlantic Dondersiidae, four aspects; radular membrane not shown. One denticle is missing from the teeth in the lower two drawings (Specimen from 805 m, 39°51.3'N, 70°54.3'W). Scale in mm.

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