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Abstract

Although the phylum Gastrotricha is known and studied for more than 150
years, some cell types, tissues and organ systems are still not well
understood in terms of their morphology, ultrastructure, function and
role. One of these features is the epidermal gland system (EGS). As yet,
there is just a single detailed electron microscopic investigation of
the epidermal glands of the species Turbanella cornuta Remane, 1925,
plus scattered ultrastructural data of few additional species. We
comprehensively investigated the epidermal glands of Tetranchyroderma
suecicum Boaden, 1960 by means of serial sectioning and transmission
electron microscopy (TEM) and with scanning electron microscopy.
Furthermore, light microscopical, confocal laser scanning microscopical
and micro-computed tomographical (mu CT) techniques were additionally
used for this investigation. Computer programs for 3D-reconstructions
were used to analyse the data obtained by TEM and mu CT.
Tetranchyroderma suecicum possesses up to 100, mostly pairwise arranged,
glandulocytes. Each single-celled gland contains a large anastomosing
secretory cistern with granular content, has a very electron-dense
cytoplasm, a basally positioned nucleus, peripherally arranged
mitochondria and a cuticulated, 'chimney-like' apical neck, which
carries the cellular pore. Each merocrine glandulocyte is associated
with an adjacent ciliated sensory cell. There is currently no coherent
hypothesis of the glandulocytes' functional role, but different ideas
are discussed. We refer to evidence that the secretory product of the
EGS of Tetranchyroderma suecicum most likely acts as a repellent against
potential predators.