Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: rabdozomy

Sortuj według:

Ogranicz wyniki do:

Artykuł dostępny w postaci pełnego tekstu - kliknij by otworzyć plik

Silurian retiolitids of the East European Platform

100%

Kozlowska-Dawidziuk A.

Acta Palaeontologica Polonica

1995

tom 40

nr 3

261-326

Late Llandovery to late Ludlow isolated retiolitid assemblages from deep boreholes drilled in the Polish part of the East European Platform are used to restore phylogeny of the group. The process of reduction of the network skeleton (reticulum and clathria), as well as reduction of the transverse rods and change of virgula position started in the Wenlock. All Ludlow retiolitids have a central virgula and reduced rhabdosomes. Colonies of the Gothograptus lineage with finite growth, related to reduction in the number of thecae, first appeared in the Late Wenlock and continued in the Ludlow. Their evolution leads either to development of finite rhabdosomes with few thecae (Holoretiolites) or to almost complete reduction of clathria and reticulum (Plectodinemagraptus gen. n. of the Plectograptus lineage). The latter homeomorph of the Ordovician abrograptid Dinemagraptus is the last known retiolitid of late Ludlow age (Cucullograptus hemiaversus /C. aversus Zone). The family Retiolitidae consists of five separate lineages. Sokolovograptus polonicus sp. n., Neogothograptus gen. n., Holoretiolites atrabecularis sp. n., Semiplectograptus urbaneki gen. et sp. n., Plectodinemagraptus gracilis gen. et sp. n. are proposed. S. polonicus from the Cyrtograptus murchisoni Zone has a strongly reduced rhabdosome.

The ultrastructure of some Ordovician graptoloid prosiculae

100%

Bates D. E. B.

Acta Palaeontologica Polonica

1996

tom 41

nr 1

39-57

The graptoloid prosicula (conus and cauda) forms the first part of the growing colony, and was probably secreted during a single continuous episode of growth. The wall is composed of a central unit of criss-cross fibrils (fusellar fabric), interlaced with parallel fibrils whose grouping appears as the spiral line (spiral line fabric). The conus is lined with a granular or felted sheet (sheet fabric). The diaphragm, at the apex of the conus, appears to be formed of fusellar fabric. The cauda is formed of fusellar and spiral fabrics with a central cavity apparently not open to the conus interior. An outer layer (diamond, mesh fabric) of fibrils forming a diamond mesh covers both conus and cauda, and is itself overlain by longitudinal rods. The apex of the cauda is formed of a second domed diaphragm of criss-cross fibrils, covered by a sheet fabric. The nema is extended distally as a series of finger-shaped increments, overlain by bandages. An outermost layer of clustered fibrils (stellate fabric) is occasionally present, lying on, or formed by a modification of, the diamond mesh fibrils of the conus.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Bates D. E. B.

1 Kozlowska-Dawidziuk A.

1 1996

1 1995

Wyniki wyszukiwania

Silurian retiolitids of the East European Platform

The ultrastructure of some Ordovician graptoloid prosiculae