File:American malacological bulletin (1988) (18152866202).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

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
Fig. 1. Schematic cross section through an adult Lepidopleurus ca- jetanus, left half (a, articulamentum; be, body cavity; f, foot; g, girdle covered with spicules; gi, gill; I, lateral fold; s, secretory cells of the foot epithelium in the pallial groove; t, tegmentum with numerous incorporated aesthetes) (adapted from Maile, 1981). (number of megapores), with about 150 per mm2 in the lateral and 90 per mm2 in the median area. The head valve has the highest density of aesthetes, about 200 per mm2. In untreated shell valves, each megapore is filled with the apical cap of the main stem (= megalaesthete) of an aesthete (Fig. 2). Each micropore contains the subsidiary cap of a micraesthete, which is a branch from the megalaesthete. In older aesthetes, the apical caps show a perforation with many pores of about 0.1 /<m in diameter (Fig. 5). The subsidiary caps do not exhibit such a pattern. In young aesthetes the apical cap is completely covered by the periostracum. AESTHETES The aesthetes are, like the papillae in the girdle, ex- tensions of the epidermis. Most of the cells of the aesthete are still connected with the epithelium via the aesthete canal. Some of these basal cell extensions are nervous elements and run further to the lateral nerve cords. Each aesthete is about 110 long and 30 /im thick. It contains 35 to 40 cells of five distinct cell types: secretory cells, central cells, photoreceptor cells, micraesthete cells branching from the main stem, and peripheral cells (Fig. 2). Except for the micraesthetes, every type can exhibit a basal extension to the epithelium (Fischer, 1978a); for the micraesthete cells the situation is not yet clear. At the shell surface the main stem is covered by the apical cap and each micraesthete by a subsidiary cap. APICAL CAR The apical cap consists only of organic material and can be divided into two zones (Fig. 2): the distal part, containing numerous parallel pores and the proximal part, consisting of a network of thin filaments of two types. There are filaments of about 80 nm in diameter, which form ac sc
Text Appearing After Image:
10 urn 2 Fig. 2. Schematic longitudinal section through an aesthete (ac, apical cap; aec, aesthete canal; c, central cell; mi, micraesthete; n, neurites; p, peripheral cell; ph, photoreceptor cell; sc, subsidiary cap; se, secretory cell). the skeleton, from which 25 nm wide filaments branch off (Fig. 6). These fine filaments form the border of the cap to the in- terior of the aesthete. SECRETORY CELLS. Each aesthete has three to eight tall secretory cells of different forms. Some of them, especially in young aesthetes, show a high metabolic activity in the pro- ximal part; granular endoplasmic reticulum (ER), a few Golgi apparatus and numerous mitochondria surround an active nucleus. The secretory granules produced are stored distal- ly. Most of the secretory cells are densely filled with mem- brane bound secretion granules of various electron densities (Fig. 7). The nucleus lies basally, its chromatin is highly con- densed (Fig. 8). Remains of endoplasmic reticulum and a few mitochrondria are often present nearby. One or two secretory cells that open distally secrete material beneath the apical cap. Some cytoplasm between the former granules remains; the interior is now continuous with the extracellular space beneath the apical cap (Fig. 9). In the neighbourhood of these

Note About Images