The fine structure of the virgular apparatus in Cystograptus vesiculosus
Adam Urbanek, Tatyana N. Koren' and Piotr Mierzejewski
Lethaia 1982, 15, 207-228
Fragments of a virgular apparatus (nematularium), assigned to
Cystograptus vesiculosus (Nicholson, 1868), etched out of
calcareous intercalations of early Llandoverian age from the South
Urals, were investigated with the TEM and light microscope. The
extrarhabdosomal portion of the nematularium is a three-vaned,
single-walled structure, built exclusively of fusellar tissue without
any cortical covering. Its surface is free of cortical bandages. No
traces of an extension of the nema (virgula) proper were found at
the junction of all three vanes. The membranous portion of each
vane is made of narrow, densely packed strips set at 6-12 degrees to
its thickened rim. These microfusellus-like units show highly
characteristic undulations of their outer pellicle, providing an
additional reinforcement of the structure. Thickened rims are made
by the merging of numerous microfuselli which, in their outer part,
have a pellicle with a thick outer lamella. A reconstruction of the
fine structure of the nematularium is suggested and possible
explanations of its morphogenesis and function are discussed.
Diagram showing the main components of the
nematularium. Legend: m- membranous
portion, t- thickened rims, V- vanes of the
nematularium, s- suture between the
microfusellar systems of both primary vans.
Reconstruction of the nematularium seen in
transverse section and showing the junction (mp)
of all three vanes.
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