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Graptolodendrum mutabile n.gen., n.sp. - an aberrant dendroid graptolite

100%

Kozlowski R.

Acta Palaeontologica Polonica

1966

tom 11

nr 1

A representative of the order Dendroidea, described as Graptolodendrum mutabile n.gen., n.sp., differs from other dendroid graptolites in its bithecae whose position is not stabilized. Mostly, they occur on one side of the stipe and, rarely, on both sides alternatively which is a rule in the Dendroidea. The fusellar structure of autothecae, mostly irregular in the distal part, is also unstabilized. The position of the pore which pierces the wall of metasicula, as in the Graptoloidea, and not of prosicula, is a fully exceptional character in the representative of the Dendroidea. The material in vestigated has been etched out from the Middle Ordovician erratic boulders of Poland.

The ultrastructure and building of graptolite dissepiments

80%

Urbanek A., Mierzejewski P.

Acta Palaeontologica Polonica

2009

tom 54

nr 2

243-252

Dissepiments or connecting bars between adjacent stipes in rhabdosomes of dendroid graptolites were studied by means of electron microscopy (SEM and TEM). The material, chemically isolated from rock matrix, originating from the Ordovician of Estonia and glacial boulders of Baltic origin found in Poland, is assigned provisionally to the genus “Dictyonema” sensu lato. Early growth stages of dissepiments are made only of the fusellar component. Older dissepiments are composed of the central core and the outer envelope: the central core is made of rather irregularly arranged growth units made of the fusellar tissue, whereas the outer envelope has a distinct cortical appearance. TEM observations indicate that the fusellar component is made of both typical fusellar and microfusellar tissues (the latter with complete and reduced microfuselli). The cortical component of dissepiments is made both of dependent and independent cortex. The opinion is advanced that the dissepiments were constructed externally by the mortaring activities of zooids, similar to that of Recent Cephalodiscus. Our observations indicate that bizooids were most probable dissepiment constructors. These results, in general, does not support earlier opinions that dissepiments are made of cortical tissue acquiring a fusellar aspect in some cases, and that dissepiments were produced by the extrathecal membrane surrounding the rhabdosome.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Kozlowski R.

1 Mierzejewski P.

1 Urbanek A.

1 2009

1 1966

Wyniki wyszukiwania

Graptolodendrum mutabile n.gen., n.sp. - an aberrant dendroid graptolite

The ultrastructure and building of graptolite dissepiments