Ducts of the labral glands of Leptestheria dahalacensis (Crustacea: Branchiopoda: Spinicaudata).
Inside the labrum of Leptestheria dahalacensis are situated three types of large epidermal gland cells, whose ducts open onto the outer dorsal surface of the labrum. SEM revealed that the thin ducts of the A-type gland cells open out behind the epipharynx at the end of small, conically shaped protuberances, the two paired ducts of the B-type gland cells lead into the distal portion of the labrum, and the external opening of the single duct of the C-type gland cells lies on the dorsal lobe of the labrum. The ducts of the three different gland cell types have the same fundamental constitution, but vary in diameter. Each secretory unit consists of a pair of gland cells (A, B, or C) and a secretory duct. The duct is formed by ring-shaped folding of one anteroposteriorly elongated epidermal cell (duct cell), whose ends adhere closely to one another. A further ring-folded epidermal cell (accessory cell), but flattened in shape, is interposed, like a sleeve-connection, between the gland cells and the duct cell. The reservoirs of gland cells open into the lumen of the duct. Discontinuous deposits of highly electron-dense matter are present on the plasma membrane of the accessory cell delimiting the initial part of the duct lumen, while the plasma membrane of the duct cell facing the lumen is cuticularized. The cytoplasm of the accessory cell, on examination by TEM, appears quite similar to that of the duct cell, except for the different distribution and greater abundance of microtubules. Similarly organized tricellular tegumental glands also commonly occur in other Crustacea, both Malacostraca and non-Malacostraca. Possible functions of secretions from the three different types of gland cells present in the labrum of L. dahalacensis are discussed.
Zeni
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C
Department of Morphology and Embryology, Section Comparative Anatomy, University of Ferrara, Ferrara, Italy. zen@dns.unife.it
Stagni
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A
D000818:Animals; D003445:Crustacea / Q000033:anatomy & histology*; D005088:Exocrine Glands / Q000033:anatomy & histology* / Q000166:cytology / Q000648:ultrastructure*; D005260:Female; D006257:Head / Q000033:anatomy & histology; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning