Chamber growth in ammonites inferred from colour markings and naturally etched surfaces of Cretaceous vascoceratids from Nigeria

Cretaceous Vascoceras and Jurassic Lytoceras show colour markings and etched surfaces representing original organic membranes between the septa. The main difference between the formation of ammonite and Nautilus chambers involved the continuous secretion of a gelatinous cameral liquid to support the ammonite mantle when it moved forward. The gel containing cyclically secreted membranes. here named pseudosepta, resembled the intra-cameral structures of the cuttlebone in Sepia. Pseudoscpta are attached to the shell wall in pseudosutures (Pseudoloben) which are particularly visible in the saddles of the septal suture and tend to mimic them. Their shape suggests reconstruction of posterior mantle shape during translocation. Drag-bands (Schleppstreifen) are spiral markings formed by the overlapping pseudosepta along the axial traces of the foliole folds. The chamber of ammonites was formed by a locally muscular mantle in a tripartite cycle: (1) the mantle initially remained attached to the saddles of the completed septal suture while muscular tissue within the umbilical lobes was contracted and rapidly reattached to the side of the lateral saddles; (2) the whole mantle subsequently crept forward by secreting a gelatinous matrix which contained telescoped membranes, with an adhesive function on pseudolobc flanks; (3) the mantle almost ceased to move within the sites of future lobules, but expanded and crept on before forming the mural and 'gutter' ridges of the septum. □ Ammonites, chamber growth, vascoceratids, LYTOCERAS, Nigeria.     

Feedback of carbon and nitrogen cycles enhances carbon sequestration in the terrestrial biosphere

The efforts to explain the ‘missing sink’ for anthropogenic carbon dioxide (CO₂) have included in recent years the role of nitrogen as an important constraint for biospheric carbon fluxes. We used the Nitrogen Carbon Interaction Model (NCIM) to investigate patterns of carbon and nitrogen storage in different compartments of the terrestrial biosphere as a consequence of a rising atmospheric CO₂ concentration, in combination with varying levels of nitrogen availability. This model has separate but closely coupled carbon and nitrogen cycles with a focus on soil processes and soil–plant interactions, including an active compartment of soil microorganisms decomposing litter residues and competing with plants for available nitrogen. Biological nitrogen fixation is represented as a function of vegetation nitrogen demand. The model was validated against several global datasets of soil and vegetation carbon and nitrogen pools. Five model experiments were carried out for the modeling periods 1860–2002 and 2002–2100. In these experiments we varied the nitrogen availability using different combinations of biological nitrogen fixation, denitrification, leaching of soluble nitrogen compounds with constant or rising atmospheric CO₂ concentrations. Oversupply with nitrogen, in an experiment with nitrogen fixation, but no nitrogen losses, together with constant atmospheric CO₂, led to some carbon sequestration in organismic pools, which was nearly compensated by losses of C from soil organic carbon pools. Rising atmospheric CO₂ always led to carbon sequestration in the biosphere. Considering an open nitrogen cycle including dynamic nitrogen fixation, and nitrogen losses from denitrification and leaching, the carbon sequestration in the biosphere is of a magnitude comparable to current observation based estimates of the ‘missing sink.’ A fertilization feedback between the carbon and nitrogen cycles occurred in this experiment, which was much stronger than the sum of separate influences of high nitrogen supply and rising atmospheric CO₂. The demand‐driven biological nitrogen fixation was mainly responsible for this result. For the modeling period 2002–2100, NCIM predicts continued carbon sequestration in the low range of previously published estimates, combined with a plausible rate of CO₂‐driven biological nitrogen fixation and substantial redistribution of nitrogen from soil to plant pools.     

Segmental growth in planulate ammonites: inferences on costal function

Checa, Antonio & Westermann, Gerd E. G. 1989 01 15: Segmental growth in planulate ammonites: inferences on costal function. Lethaia , Vol. 22, pp. 95–100. Oslo. ISSN 0024–1164.
In planulate Ammonitina, the directions of costae and their parts coincide with the growth lines, both being accreted in parallel and subtriangular increments, i.e. segments. This implies that the growing margin was consistently corrugated (plicated) parallel to the edge of the peristome. The adventral separation of the ribs caused by the coiling increased with whorl involution and was compensated for by costal division into primaries and secondaries. We propose that costation of the shallow-water, nekto-benthic plandates reduced the stiffness and increased effective thickness of their growing peristome. Ribs functioned (primarily or secondarily) as a protection for the immature, fragile aperture against predators and impacts.□ Ammonite shell, Jurassic, morphology, growth lines, ornamentation, costae .     

Ultrastructural Investigation of the Integument of Tubiluchus philippinensis (Priapulida, Tubiluchidae)

The integument of Tubiluchus philippinensis van der Land, 1984 has been investigated by means of scanning and transmission electron microscopy. The ultrastructure of the cuticle corresponds principally to what has been found in Priapulidae. The tumuli are mere cuticular thickenings. Setae, tubuli, flosculi and scalids are receptor organs. Tubuli additionally serve a second function: they produce a secretion. The male genital area is equipped with various receptor organs, the internal morphology of which has been described. All receptor cells are characterized by apical cilia, which may be surrounded by a circlet of microvilli. They sometimes bear a rather complicated rootlet apparatus.     

New Harpacticoida (Crustacea, Copepoda) from the North Atlantic Ocean. VIII. The description of Eurycletodes (Oligocletodes) quadrispinosa sp.n. and the male of E. (O.) monardi Smirnov (Cletodidae)

Eurycletodes (O.) quadrispinosa Sp.n. and the male of Eurycletodes (O.) monardi are described. E. quadrispinosa differs from the closely related species E. echinatus Lang, E. parasimilis Por and E. arcticus Lang in the setation of segment 1 and 2 Exp P2–P4, of segment 2 Exp p24 and of the Exp P5. Because of the same setation of the A2, Pl-P4 Exp and Exp as the female of E. monardi Smirnov the described male is regarded as that of E. monardi Smirnov. The species were collected at the Iceland Faroe Ridge from depths of 500. 1540 and 2500 m.     

Isolation and amino acid composition of the adipokinetic neuropeptide from the corpus cardiacum of the cricket, Gryllus bimaculatus

ABSTRACT. The corpora cardiaca of the cricket, Gryllus bimaculatus De Geer, contain peptidic material which elicits hyperlipaemia in migratory locusts and in crickets. Appreciable amounts of this adipokinetic factor are found only in the corpora cardiaca of the cricket, and not in other parts of the nervous system. The factor is heat-stable and retains its activity after incubation with the exopeptidases leucine aminopeptidase and carboxypeptidase A. Fractionation of a methanolic extract of corpora cardiaca from Gryllus bimaculatus by RP-HPLC shows that the adipokinetic activity is confined to a single absorbance peak. The amino acid composition of the purified adipokinetic neuropeptide was determined after acid hydrolysis with HCI and with methanesulfonic acid. The factor is an octapeptide containing the following amino acid residues in equimolar amounts: Asx, Thr, Ser, Glx, Gly, Val, Phe and Trp. This composition closely resembles the AKHI II molecule from Schistocerca species , and the Gryllus peptide can be assigned to the AKH/RPCH family of neuropeptides.