File:American malacological bulletin (1988) (18129862326).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. 1. Schematic cross section through the girdle (a, articulamen- tum; ae, aesthetes in the tegmental shell layer; c, cuticle; cl, clap- per; ct, connective tissue; ds, dorsal scales; h, hair; ms, marginal spines; t, tegmentum; vs, ventral scales) (after Maile, 1981). electrode at the very first contact, general pressure on the girdle, instead of the touch of single elements in the girdle, can be excluded as a cause of the observed reactions, e.g. avoidance behavior. The reactions were classified into four categories of increasing intensity: movement of touched ele- ment; movement of neighbouring elements; girdle movement near the touched place; whole animal moving away. The fre- quencies of these avoidance behavior patterns were deter- mined by direct observation. Each of 20 animals was tested several times (depending on the overall activity, that can make the tests quite difficult) and in all areas (dorsal scale, marginal spine, hair, ventral scale). The chitons were light-adapted for at least one hour (dark-adapted animals exhibit a marked response to light (Bergmann, 1986)). The chitons had been kept in aquaria containing artificial sea water (20°C, natural day/night-cycle, simulation of high and low tides) for 6 months up to 3 years before the tests. RESULTS MORPHOLOGY OF THE GIRDLE The girdle of Chiton olivaceus is covered with characteristic calcareous parts (Fig. 1). On the dorsal surface, large scales are arranged like tiles on a roof, with the open side directed towards the shell. The tallest scales (up to 180x130 /urn) are found in the middle part of the girdle, whereas those near the girdle margin and near the shell valves are much smaller (50x20 /xm). In most cases, the surface of the scales shows irregular elevations and ridges (Figs. 2, 3). The girdle margin is formed by one row of calcareous spines (50-90 f»m long and 20-25 wide). They bear thin ridges running roughly parallel to their long axes (Fig. 2). Between the marginal spines and the dorsal scales, hair-like forma- tions can be observed at regular distances. One hair is nor- mally accompanied by one or two clapper-like structures. Each hair or clapper consists of a solid shaft of organic material and a calcareous tip, which can be lost in some hairs. The hair shaft is 70-110 long and between 5 /tm (at the base) and 1.5 /*m wide (distally). The calcareous tip structure can reach a length of 30 jim and a diameter up to 4 iim. The organic shaft of the clappers is 10 /im long and 2 /tin wide; the calcareous tip is 10-15 itm long and about 7 /xm in width.
Text Appearing After Image:
Fig. 2. Scanning electron micrograph of the girdle margin (cl, clapper; cti, calcareous tip of a hair or clapper; c, cuticle; ds, dorsal scale; h, hair; ms, marginal spine). Fig. 3. Isolated dorsal scale, KOH-treated. A groove (arrow) shows the connection site with the spicule cell of the papilla. Fig. 4. Ventral scales (right side is lateral).

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