Conellae, enigmatic structures on cephalopod shells—shapes, distribution, and formation

Conellae, enigmatic cone-shaped structures which can be found on the surface of internal moulds of cephalopod shells (predominantly of ammonoids), are regarded herein as the product of remote (biologically induced) biomineralization formed in closed-off cavities during lifetime and might be primarily composed of vaterite, aragonite, or calcite. To date conellae have been interpreted in many different ways: (i) as organisms (gastropods, cirriped crustaceans, or disciniscid brachiopods), (ii) pre-diagenetic syn vivo features, i.e., biologically controlled or induced, the product of remote biomineralization, (iii) and diagenetic, i.e., abiogenic origin and post-mortem. The proposed processes of conellae formation seem insufficient to explain conellae related phenomena. Further, their assumed primary aragonitic or calcitic mineralogy are reviewed and based on new material critically assessed. The stratigraphic range of conellae extends from the Middle Ordovician and probably to modern Nautilus. Predominantly, conellae can be found on internal moulds along the keel, ribs or nodes, umbilical shoulder, at the transition between phragmocone and body chamber, and can be associated with repaired scars. However, conellae are also common on the smooth body chambers of large macroconchs of Jurassic ammonites. Conellae, which are located on ammonite body chambers, are filled with the same material found in the body chamber and can contain small burrows, sand grains, or coprolites. Some of these conellae are partially covered with nacreous shell material. Limonitic conellae were also found on the limonitic internal moulds of orthocone nautiloids. Moreover, disciniscid brachiopods found on inoceramid bivalves were re-identified herein as conellae. A short guide for conellae identification has been provided herein

Form and formation of flares and parabolae based on new observations of the internal shell structure in lytoceratid and perisphinctid ammonoids

The ultrastructure of pristine shells of Jurassic and Cretaceous lytoceratid and perisphinctid ammonoids indicates that flares and parabolae represent homologous structures. Both mark an interruption of shell growth. We dismiss earlier interpretations of parabolae as actual aperture, relics of resorbed apophyses or superstructure of the musculature associated to a semi-internal shell. Instead we propose an episodic growth model including several growth stops at the aperture during the formation of a frill-like aperture for parabolae and flares. Such an aperture is composed of the outer prismatic layer, the nacreous layer and an apertural prismatic coating. Here, we observed the apertural prismatic coating for the first time as an integral part of flares and parabolae. The apertural prismatic coating covers only the inner surface of the frill and was secreted by a permanent mantle cover indicating a prolonged period without the production of new shell material. Parabolae differ from flares by their general shape and the presence of ventro-lateral parabolic notches and nodes. The notches were formed by folding of the frill and had the potential to form semi-open spines. The corresponding parabolic nodes are caused by an outward swelling of the shell-secreting mantle tissue producing new shell material at the position of the folding. New shell material that belongs to the conch tube is attached to the base of flares and parabolae after withdrawal of the mantle edge representing the continuation of shell growth. Usually, the frilled aperture associated with flares and parabolae were removed during lifetime. This study reports on flares in Argonauticeras for the first time. In this genus they are typically associated with varices

Modulation - ein Ansatz zur Neuorientierung der Agrarpolitik?

In jüngster Zeit werden der Landwirtschaft neben der Nahrungsmittelproduktion weitere Aufgaben zugeschrieben, die bisher teilweise kostenloses Koppelprodukt waren und jetzt gezielt gegen gesonderte Honorierung erbracht werden sollen. Im vorliegenden Beitrag untersuchen Martin Kapfer, Prof. Dr. Alois Heißenhuber und Prof. Dr. Helmut Hoffmann, Technische Universität München, die mit der Agenda 2000 eingeführte Neuausrichtung der Agrarpolitik, wobei sie insbesondere auf die so genannte Modulation eingehen.Landwirtschaft, EU-Agrarpolitik, Europäische Wirtschafts- und Währungsunion

Impact of AC and DC Electric Fields on the Microstructure Evolution in Strontium Titanate

Herein, the impact of AC and DC electric fields on microstructure evolution in strontium titanate is investigated. The focus is on nonthermal effects by using current-blocking electrodes. The seeded polycrystal technique allows investigating the impact of a DC electric field on grain growth for different grain-boundary orientations and the impact of the surrounding atmosphere. As in previous studies, faster grain growth is observed at the negative electrode. This effect is stronger for the (100) orientation and in reducing atmosphere. In AC electric field at 1450 °C, a low-enough frequency results in faster grain growth at both electrodes. These findings agree well with previous studies, where an electromigration of oxygen vacancies is found to cause a local reduction at the negative electrode, resulting in less space charge, less cationic segregation, and a higher grain-boundary mobility. At 1500 °C, AC electric fields are found to cause a complete grain growth stagnation at very small grain sizes. This behavior is unexpected; the physical reasons are not clear. Herein, a brief study of sintering in DC electric field reveals slightly faster sintering if a field is applied

Enhancement of the photochromic performance of spirooxazine in sol-gel derived organic-inorganic hybrid matrices by additives

Organic-inorganic hybrid materials synthesized via sol-gel processing are excellent solid matrices for photochromic dyes like spirooxazine, and the photochromic performance can be further enhanced by introducing suitable additives. This work describes the effects of additives on the photochromic intensity (ΔA0), decolouration rate (k) and photostability of spirooxazine in sol-gel derived organic-inorganic hybrid matrices. They include fluoro-alkylsilane (FAS), bisphenol A (BPA) and methyl-imidazole (MI). FAS enhances both ΔA0 and photostability, but has little effect on k. The higher the content of BPA, the higher the ΔA0 and the higher the photostability, but the lower the k. The effect of MI on ΔA0 and k is not so considerable as that of BPA and is a little complicated, while significant improvement in photostability is achieved by the addition of MI at an optimum concentration with the presence of BPA at a higher content

Preparation and photochromic properties of dye-doped aluminosilicate ORMOCER gels and coatings

Aluminosilicate and ORMOCER gels and coatings containing photochromic dyes, 1, 3-dihydro-1, 3, 3-trimethylspiro-[2H-indole-2, 3\u27-[3H]-naphth-[2, 1-b][1, 4]-oxazine] (SO) and 1\u27, 8a\u27-dihydro-2\u27, 3\u27-dimethoxycarbonyl-spiro [fluorene-9, 1\u27-indolizine] (DHI), were prepared by the sol-gel method and the photochromic activity was monitored in the course of the sol-wetgel-xerogel transformation. The photochromic activity of the aluminosilicate gels decreases rapidly and even vanishes in the wetgel-xerogel stage while that of ORMOCER gels and coatings levels off in the early wetgel-xerogel stage at a reasonably high photochromic intensity with the colour-fading speed similar to that in ethanol and the photostability being considerably improved. The experimental results are discussed in terms of the matrix effect on photochromism of organic dyes

‘Arm brains’ (axial nerves) of Jurassic coleoids and the evolution of coleoid neuroanatomy

Although patchy, the fossil record of coleoids bears a wealth of information on their soft part anatomy. Here, we describe remains of the axial nerve cord from both decabrachian (Acanthoteuthis, Belemnotheutis, Chondroteuthis) and octobrachian (Plesioteuthis, Proteroctopus, Vampyronassa) coleoids from the Jurassic. We discuss some hypotheses reflecting on possible evolutionary drivers behind the neuroanatomical differentiation of the coleoid arm crown. We also propose some hypotheses on potential links between habitat depth, mode of life and the evolution of the Coleoidea