Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico

Toomey. Donald F. & Cys. John M. 1979 01 15: Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico. Lethaia , Vol. 12. pp. 65–74. Oslo. ISSN 0024–1164.
Small organic mounds outcrop in the Lower Permian Laborcita Formation of the northern Sacramento Mountains of southcentral New Mexico. These small organic structures, up to I'm in height and 3 m in diameter, are unique because they show a well developed vertical biolic zonation. This zonation consists of an initial pioneer community composed of small digitate or plumose colonies of algae and foraminifers (Stage 1). This is followed by a climax community that is first dominated by laminar colonies of the red alga Archaeolithophyllum (Stage 2). and followed by a terminal community composed of minor Archaeolithophyllum , erect heliosponges and brachiopods, dominated by the form Composita (Stage 3). Evidence suggests that the mounds initially developed in shallow water within an open lagoon but. with continued transgression and rapid deepening of the depositional environment. the biota responded to the changes. The organic buildups were killed off by sudden influx of clastics from a tectonically active nearby landmass.     

Learning in Stentor

SYNOPSIS. When placed in a vertical capillary tube of 0.5 mm inner diameter opening at the bottom end into a reservoir, Stentor coeruleus learns to escape; that is, on the 1st trial it takes a long time to find its way out and much less time on the 2nd and succeeding trials. It was found that learning did not occur in a horizontal tube, or in a vertical tube with the open end above, or in tubes of 1 or 2 mm inner diameter. To explain the results it is suggested that the response is actually a delayed geotaxis released only after a definite period of mechanical stimulation from bumping into the walls of the tube. Possibly the phenomenon is related to the process of habituation to mechanical stimuli which has been elucidated by other authors.     

The Development of Host-Type {theta} and TL Antigens in Nude Mice after Transplantation of a Neonatal Thymus

Thymus cells from the BALB/c and AKR mouse strains can be distinguishedby the 8 and TL surface antigens. When a BALB/c-nunu (athymic)mouse is grafted with a neonatal AKR thymus, the great majorityof the cells of the grafted thymus retain AKR characteristicsfor about 12 days. Between day 12 and day 26 both host- anddonor-type cells can be found, but after day 26 there are onlyhost-type cells. The differentiation of host-type T cell precursorsrequires the presence of thymus epithelium and perhaps actualthymus structure.     

Rides septales à organisation de type tétracoralliaire chez Trachypsammia (Tabulata, Permien)

Précédemment décrite chez Kerforneidictyum et Palaeacis I'organisation des rides septales suivant un schema de type tetracoralliaire est reconnue chez Trachypsammia monoseptata (Permien de Timor) où n'avait été signalé qu'un fort “Medianseptum”. II détermine un plan de symétrie bilatérale dans le calice; la ride cardinale forte est en position dorsale ou interne, la ride antipode également bien développée en position ventrale ou externe souvent plus courte, les rides considérées comme alaires sont identifiables au moins dam leur partie proximale. L'ensemble des rides clairement observables sont les rides majeures (protorides et métarides), les rides mineures sont à peine ébauchées. T. monoseptata pourrait représenter un stade calicinal jeune de T. dendroides. Trachypsammia dendroides (Permien de Timor) posséde un plan de symétrie bilatérale net. la ride cardinale est plus forte et plus longue que les autres rides, la ride antipode plus courte, les rides alaires sont identifiables en coupe transversale. rides majeures el mineures sont bien differenciées; le nombre total de rides est souvent de 32. Chez T. xizangensis (Permien du Tibet), seule une symétrie bilatérale a été observée en coupe. Pas de donnees pour T. mrditerranea (Permien de Sicile). Les affinités systéinatiques très étroites mises en évidence entre Polaeacis et Trachypsammia par les caractéres microstructuraux sont confirmées par Ie dispositif septal, ces Tabulés constituent-ils un groupe particulier? La question est posée A rugosan pattern of the septal ridges, formerly described in Kerforneidictyum and Palaeacis is pointed out in Trachypsammia monoseptata (Permian of Timor) for which only the ‘Medianseptum’ had been observed. T. monoseptata exhibits a strong cardinal ridge in dorsal or internal position. just opposite a shorter counter ridge, thus creating a plane of bilateral symmetry. The ridges assumed to be alar can be identified by their proximal ends being in contact with the ‘Medianseptum’. The major ridges (proto and metaridges) are obvious, the minor ones show only their very proximal ends. T. monoseptuta could be a calicinal young stage of T. dendroides. T. dendroides (Permian of Timor) shows a plane of bilateral symmetry, the cardinal ridge is stronger and longer than the others, the counter shorter, the alar ridges can be identified in transverse section. major and minor ridges are well developed; the number of ridges is often 32. In T.xizangensis (Permian of Tibet) only the bilateral symmetry is known, while there are no data for T mediterranea (Permian of Sicily). The systematic affinities between Palaeacis and Trachiypsammia pointed out on the basis of microstructural data are also supported by the septal ridges pattern. Do Palaeacis, Trochypsammia and others form a special division of Tabulate corals? That is the question