THE CEREBRAL GANGLIA OF MILNESIUM-TARDIGRADUM DOYERE (APOCHELA, TARDIGRADA) - 3-DIMENSIONAL RECONSTRUCTION AND NOTES ON THEIR ULTRASTRUCTURE

Differential interference contrast micrographs from stretched animals, serially sectioned semi-thin and ultrathin sections revealed that the cerebral ganglia (supraoesophageal mass) of the eutardigrade Milnesiu m tardigradum lie above the buccal tube and adjacent tissue like a sad dle. It has an anterior indentation which is penetrated by two muscles that arise from the cuticle of the forehead. The cerebral ganglia con sist of lateral outer lobes bearing an eye on each side, and two inner lobes which extend caudally. Between the inner lobes a cone-like proj ection tapers into a nerve bundle. Each outer lobe is joined with the first ventral ganglion. From the outer lobe near the eye the ganglion for a posterolateral sensory field extends to the epidermis. Anterior to the supraoesophageal mass are three dorsal ganglia for the upper th ree peribuccal papillae. Two additional ganglia attached to the cerebr al mass supply the lateral cephalic papillae. The cerebral ganglia are covered by a thin neural lamella. The pericarya which surround the ne uropil have large nuclei. Near the axons in the centre of the supraoes ophageal mass the cytoplasm is crowded with vesicles of different size and appearance. Some of them resemble synaptic vesicles while others resemble dense sore bodies. Structurally different types of synapses a nd axons can be distinguished within the neuropil. (C) 1996 The Linnea n Society of London