Mszywioły mioceńskie z okolic Opatowa

Jerzy Małecki


Miocene bryozoa from the Opatów environ (Central Poland)

The author has examined the Bryozoa of the species Sohizoporella tetragona (Reuss) from sandy deposits of the Lower Tortonian in the Opatów area. He observed that during development of zoaria of this species there occurred superposition of the zooecia layers. The first zoarium, surrounding the plant stalk, showed a very regular arrangement of zooecia (Pl. II, figs. 2, 3; Pl. Ill, fig. 7). It was „attacked” by larvae of this species, which attached themselves to the frontal walls of zooecia, giving rise to new zoaria. The specimens of the first zoarium defended themselves, hindering the normal development of the new-formed zoaria. Due to this, the side walls and partly the apertural walls of the new specimens, as well as their avicularia, were deformed. However, the arrangement of zooecial series was preserved. The formation of further layers of this multilayer zoarium proceeded at random. Attached to the frontal wall, the larvae could not develop properly because of the polypides protruding from the apertures of the lower layer and due to protective activity of avicularia. Observation of respective layers within the zoarium reveals that the apertures of specimens belonging to the lower layer are frequently surrounded by narrow, high zooecia of the upper layers, i.e. they are in deep interzooecrail cavities. The successive layers usually cover these cavities, due to which they are visible in cross- and longitudinal sections through the zoaria. In the upper layers of the zoarium, great diversity in the arrangement of the longer walls of zooecia has been noted. Consequently, in several plaices of the zoarium the apertures are closely spaced and due to this, the avicularia growing near the apertures are deformed and sometimes oddly situated. Owing to such development of zoaria, zooecia are frequently square, rectangular, rhomboidal or even elliptical or circular in outline. This great variability in the shape of zooecia is illustrated by the photographs and figures. If fragments of S. tetragona (Rss.) zoaria are found separately, they can be erroneously regarded as belonging to different species. In fact, a review of the synonymy of the genus Schizoporella shows that each author who dealt with the species of this genus encountered serious difficulties in assigning his specimens to appropriate species. Studies of the specimens of S. tetragona (Rss.) within the available zoaria have revealed that the variability in the shape of zooecia does not affect the shape or size of apertures or avicuilaria, which are always the same. In publications dealing with the Miocene bryozoans this species was described under different specific names, viz. tetragona, dunkeri, ansata, ansafta var. tetragona, unicornis. In the papers published after 1970, the authors began to notice close similarities within the species of the genus Schizoporella, suggesting groups referred to as ,,unicornis” or "ansata — unicornis", in which the species S. tetragona (Rss.) was placed. Considering the marked differences in the structure of zoaria, Canu and Bassler introduced a new specific name „Stylopoma” (1925) to define a multilayer zoarium. This name was criticized as groundless by David and Poyet (1974, p. 157). Significant divergences in the descriptions and determinations of the fragments of Schizoporella tetragona (Rss.) zoaria were due to insufficient knowledge of the processes leading to the formation of multilayer zoaria, growing mainly on plants. The present author investigated and described these processes, as well as revised several incorrect determinations of species of the genus Schizoporella.

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