The clypeal glands of three New Zealand Linyphiidae currently placed in Mynoglenes are described, by light, scanning and transmission electron microscopy. Shallow sulci beneath the lateral eyes of both sexes trap secretions which are produced by greatly elongated cells packed radially with respect to a given sulcus, and each voiding its product to the exterior by an individual ductule. The function of the secretion is unknown, although the ultrastructure of the gland resembles that of the defensive glands of many insects, but there is no separate duct cell, and the basal region of each secretory cell exhibits a unique strategy of membrane amplification, which divides the cytoplasm longitudinally into compartments by folds of the plasma membrane, compartments being still further subdivided into “tails”. Patterns of vacuolation observed in various regions of the cytoplasm support the hypothesis that these unusual structures may be concerned with rapid water transport from the haemocoele, and that the cells discharge their contents by a “flush-out” mechanism. It is shown that male Erigoninae with cephalic specializations have similar clypeal glands, but with cytological profiles (in alcohol-fixed material) which suggest that special forms of membrane amplification are not present. Glands are absent in female Erigoninae, and in males with unmodified heads. It is suggested that in this latter subfamily the cephalic modifications may serve as presenting surfaces for sexual pheromones.
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