MECHANICAL AND MORPHOLOGICAL PROPERTIES OF THE SHELL OF SCROBICULARIA PLANA (DA COSTA) UNDER NORMAL AND STRESS CONDITIONS

Scrobicularia plana reacts to salinity stress by closing itsvalves and respiring anaerobically. The acidic products of respirationare buffered by calcium carbonate removed from the shell. Shellmass decreases by 15% over a period of three weeks, and thereis a similar reduction in shell strength. Erosion of the shell surface, indicating buffering, takes placequickly, pits can be seen in the valves of shells at the endof six hours of normal intertidal emersion. (Received 10 February 1982;     

Ultrastructure and Sporogony of Eimeria (syn. Epieimeria) anguillae (Apicomplexa) in the Eel (Anguilla anguilla)

ABSTRACT. Ultrastructural studies on Eimeria (syn. Epieimeria ) anguillae (Apicomplexa), parasite of the digestive tract of the eel, have shown that the development of this parasite takes place completely within the host cell. Merogony and gamogony are intracellular but in the epicytoplasmic position. Sporogony is also located within the epithelial cells, which agrees with assignment of this coccidian in the family Eimeriidae. However, depending on the intensity of infection and the physiopathological reaction of the host, the gamont may behave in two ways. 1) In massive infections, gamogony stages cause a genuine destruction of intestinal epithelium. Large numbers of gamonts form nodules and parts of the seriously destroyed epithelium peel off and are released into the lumen of the gut and quickly discharged into the outer environment. This discharged epithelium envelops cells containing immature oocysts that then sporulate outside the host. 2) In light infections, the host cells, which are necrotic due to the presence of a zygote, are pushed between the surrounding intact cells towards the base of the epithelium. Closely above its basal lamella, the oocyst then undergoes sporulation. These results show no taxonomically important biological features (e.g. special mode of implantation to the host cell or active movement of the zygote). Because the morphological characteristics of Epieimeria do not differ significantly from Eimeria , we propose to suppress the genus Epieimeria Dyková and Lom, 1981, and relegate its species into the genus Eimeria .     

Kinetics of Manganese Uptake by Intact Citrus Seedlings

Uptake of manganese by intact citrus seedlings can be represented by three phases of a single, multiphasic isotherm in the range 10^?8M–2× 10^?4M. The phases are separated by marked jumps and the kinetic constants increase upon transition to higher phases.     

Effects of physico-chemical treatments on hemagglutination activity of Anopheles gambiae haemolymph and midgut extract

Abstract. Anopheles gambiae midgut extracts and haemolymph possessed agglutinins, titre 1:16 to 1:256, against human red blood cells (RBCs). Subjection of both tissues to protein precipitation reagents, organic chemical and selected protease, neuraminidase and other glycosidic hydrolase treatments revealed the haemagglutinins to be protein, most likely glycoprotein, in nature - not lipoprotein, lipid, glycolipid or nucleic acid. An.gambiae agglutinins were thermo-labile >40^oC, affected by freezing and thawing treatments, and contained disulphide and hydrogen bonds on the basis of sensitivity following exposure to dithio-threitol and urea respectively. Optimum haemagglutination depended generally on slightly acid to neutral pH conditions and agglutinin activity was Ca²⁺ ion, albeit to a lesser extent Mg²⁺ ion, dependent. The midgut extract agglutinin subunit molecule had a relative molecular weight (M_r) of 65kDa whilst that of haemolymph was 40kDa.
This study presents the first report on selected physico-chemical properties, the glycoproteinaceous nature and tentative subunit M_r of mosquito midgut extract and haemolymph anti-RBC agglutinin(s).     

An experimental study of the breakdown of submerged leaves by hyphomycetes and invertebrates in Morocco

SUMMARY. 1. Mechanisms of the breakdown of submerged leaves under the warm and dry Moroccan climate, including the interaction between hyphomycetes and invertebrates, were investigated.
2. Laboratory experiments were performed on dried leaves of Salix sp. and Nerium oleander .
3. During the first month under the experimental conditions, Melanopsis praemorsa, Physa acula (Gastropoda) and Hydropsyche maroccana (Trichoptera), respectively, were responsible for a loss of weight of 38, 21 and 13% in willow leaves, and 40, 15 and 8% in oleander leaves.
4. The weight lost by willow leaves inoculated with the fungi Alatospora acuminata, Anguillospora longissima, Lemonniera aquatica and Tetracladium marchalianum increased with time, but varied according to the fungal species. Loss of weight and increase in nitrate and phosphate content of the leaves were greatest with Lemonniera and smallest with Tetracladium .
5. When the leaves thus colonized by each of the four fungal species were exposed to each of the three invertebrates, the amount of material consumed increased with the time of fungal conditioning and varied according to the fungus and to the invertebrate. Greatest consumption was by Melanopsis feeding on leaves conditioned by Lemonniera , in which case assimilation percentage by the gastropod was as high as 75%.
6. Owing to their numbers in the field, and to the quantity of leaf material they ingest, gastropods appear as the main shredders in the streams considered, thus replacing the Crustacea that often play this part under temperate climates. Breakdown seems faster in Morocco than in France, mainly because of a shorter initial time lag in weight loss.