File:American malacological bulletin (1988) (17535794753).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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LEISE: CHITON SENSORY HAIRS 143
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Fig. 2. a. Dorsal integument of Lepidozona cooperi (Pilsbry, 1892) demonstrating overlapping scales, b. Dorsal integument of Acanthopleura granulata (Gmelin, 1791) displaying calcareous spines. Cuticle is visible between spines, c. Dorsal hairs of Placiphorella velata. Numerous spicules (arrows) are embedded near the surface of each hair (cu, cuticle; sh, shell) (from Leise, 1983). Fig. 3. Transverse 1 /<m section through the decalcified integument of Mopalia muscosa. Spicules (s) produced by spiniferous papillae (sp) contain brown pigment granules (arrow). One spiniferous papilla has produced a sensory nodule (no). Part of its stalk is not in the plane of this section. Common epidermal cells (cec) occur between papillae (from Leise and Cloney, 1982). Leise and Cloney, 1982). Similarly, in the genus Placiphorella, the hair is an extension of the cuticle and is entirely covered with spicules that lie in whorls just below the surface of the hair (Fig. 2c) (Plate, 1902). From Ferreira's (1982) descriptions, the hairs of L. flectens and the genus Dendrochiton appear likewise to be branched or compound structures and not simp- ly enlarged spicule shafts. THE MORPHOLOGY OF HAIRS OF MOPALIA MUSCOSA: A MODEL FOR COMPOSITE SENSORY HAIRS A fully-formed hair of Mopalia muscosa is a curved, distally tapered extension of the cuticle that bears a mesial groove in which lies a row of spicules (Figs. 5, 6). Each spicule occurs atop a distinct shaft, whose proximal end is embedded in the cuticular matrix, or medulla. The medulla is enveloped by a bilayered cortex, except for the mesial groove, and is therefore exposed to the environment along the length of that groove. Within the medulla, the proximal end of each spicule shaft surmounts a bulbous epidermal pro- jection, a stalked nodule (Leise and Cloney, 1982) or "morgensternformig Kdrper" (morning star-shaped body) (Reincke, 1868). Blumrich (1891), Knorre (1925), and Plate (1898, 1902) described such nodules in many species. All of these authors suggest that the nodules are tactile. Until recent- ly (Leise and Cloney, 1982), their presence in hairs of the Mopaliidae was unknown. The dorsal girdle epidermis is a single layer of cells that is divided into numerous packets or papillae of colum- nar cells. These papillae produce the hairs, spicules, and nodules. Smaller cuboidal cells occur ubiquitously between the papillae. The papillae that produce the hairs are the largest in the epidermis and as a hair matures, the papilla comes to lie in a small depression or pocket below the level of the rest of the epidermal cells (Leise and Cloney, 1982; Leise, 1986). Each subcortical cell produces a bundle of cortical fibers (Figs. 6, 7). The fiber bundles of the inner cortex are more dense than those of the outer cortex (Leise and Cloney, 1982). Each layer of the cortex in a mature hair is several bundles thick, whereas in young hairs the cortex is only one bundle wide. Newly forming hairs have no cortex and start as a single spicule with an elongated shaft that lies above a stalked nodule. More spicules and their associated shafts and nodules are added to the growing cuticular hair and on- ly after several nodules are present does cortex begin to ap- pear. The cortex is initially a narrow crescent along the lateral edge of the hair. As development proceeds, the hair grows longer and the cortex become progressively wider until it en- compasses nearly the entire shaft (Leise, 1986). Submedullary cells occur as a hillock that protrudes into the base of the hair shaft and presumably secrete the medullary matrix. The sensory cells lie in clusters within this

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