. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LIME-TWIG GLANDS 103 et «-. bt Figure 7. Scheme of a discharged lime-twig capsule: remnants of the marginal cytoplasm of the capsular cells (arrow headsl and, at the bottom, two of the nuclei are visible; bl: thickened basal lamina; ed: body epidermis covered by cuticle; et: extruded lime twig thread, discharged bv a rupture of the apical cell membrane (at the right); ip: invagination pit with mi- crovillous border, not covered b> the tough cuticle (rupture zone) (Scale bar: 10 fim). In shrunken, discharged capsules this
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LIME-TWIG GLANDS 103 et «-. bt Figure 7. Scheme of a discharged lime-twig capsule: remnants of the marginal cytoplasm of the capsular cells (arrow headsl and, at the bottom, two of the nuclei are visible; bl: thickened basal lamina; ed: body epidermis covered by cuticle; et: extruded lime twig thread, discharged bv a rupture of the apical cell membrane (at the right); ip: invagination pit with mi- crovillous border, not covered b> the tough cuticle (rupture zone) (Scale bar: 10 fim). In shrunken, discharged capsules this outer layer is about twice as thick (700-800 nm) and shows an increased elec- tron density (Fig. 6a). In several sections, beside the capsular neck, trans- versely sectioned single subepithelial nerve fibers can be seen (cf. Emschermann. 1982, 1985). some of which con- tain small vesicles resembling presynaptic vesicles (Figs. 4c. 5). However, additional indications of a synaptic con- nection between these nerve processes and the capsular cells, as well as any evidence of a nervous control of the lime-twig glands, are lacking. Discharged capsules appear somewhat shrunken, but not collapsed (Figs. 6. 7). They are empty except for re- mains of the marginal cytoplasm and, basally, the degen- erating nuclei. The extruded cuticular tubule is not evagi- nated ( everted like a glove finger as in the cnidarian spiro- and nematocysts), or released by exocytosis, as in rhabdocysts, rather it is ejected through a rupture of the apical cell membrane in the funnel area not covered by cuticle (Figs. 7. 8). After its ejection, the unfolded thread remains covered by a dense coat of the secretion vesicles described above (Figs. 7. 8). Gradually, the latter swell and give off their contents, forming a sticky mucous cover around the unfolding thread (Fig. 8). Discharged lime-twig capsules are not reloaded. Some- times, especially in older specimens, large electron-dense complexes of degener
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
