Colour polymorphism and thermal capacities in Theba pisana (O.F. Müller 1774)

Several land snail species are highly polymorphic regarding their shell colouration. This polymorphism has been related to predatory effects as well as climatic reasons, assuming that dark morphs benefit from being more cryptic and therefore less prone to predation, whereas pale morphs are at an advantage under solar radiation, as they are suspected to heat up less. However, the assumption of different thermal capacities of these morphs is based on experiments with little standardisation or little environmental relevance. In this study, we aimed at measuring thermal capacities of two different morphs (pale versus dark-brown banded) of the Mediterranean land snail Theba pisana, applying a standardised and environmentally relevant test set-up, in order to prove whether darker morphs indeed do heat up more than lighter coloured morphs. We did not find any differences in the thermal capacity of the different morphs and conclude that thermal capacity of the shell is predominantly defined by its material rather than its coloration. These results are discussed with regard to previous studies on thermal characteristics of different land snail morphs and correlations between climate and morph distribution.     

Aspects of the Cryobiology of the Intertidal Harpacticoid CopepodTigriopus brevicornis(O. F. Müller)

Cold-resistance studies of marine invertebrates have concentrated on intertidal sedentary organisms, which are often subjected to subzero air temperatures in winter. Mobile rock pool inhabitants have been rarely studied because such habitats are thought to buffer environmental variation. However, it is not uncommon for small upper-shore rock pools ( approximately 2 by 1 cm) to become completely frozen. Such supralittoral habitats are subject to extreme physicochemical fluctuations especially in salinity (0 to 300 per thousand) and temperature (-1 to +32degreesC) due to evaporation and dilution. The dominant invertebrate in such habitats is the harpacticoid copepod Tigriopus brevicornis. Aspects of the cryobiology of T. brevicornis were investigated using differential scanning calorimetry (DSC). Thermograms obtained from DSC allowed determinations of freeze-onset (supercooling point, SCP), melt-onset, and melt-peak (melting point, MP) temperatures, together with estimation of the proportion of water freezing in the samples. The effects of acclimation salinity, temperature, starvation, and reproductive state on these cryobiological parameters were investigated. Acclimation to increasing salinity depressed the SCP, with the highest salinity (70 per thousand) producing the lowest SCP, melt-onset, and MP temperatures at -27.5, -15.2, and -9.5degreesC respectively. The highest acclimation temperature (20degreesC) produced the lowest SCP (-23.4degreesC). Starvation significantly increased the SCP, melt-onset, and MP temperatures in comparison to fed individuals acclimated to the same salinity. The presence of eggs or ovaries in individual copepods elevated the SCP compared to nongravid females and males. LT50 studies showed that acclimation to high salinity improved the ability of T. brevicornis to survive in frozen seawater. Seventy parts per thousand acclimated individuals had an LT50 of 64.9 h compared with just 1.4 h for 5 per thousand acclimated individuals in frozen seawater at -5degreesC. The study shows that the cold-resistance capabilities of T. brevicornis can be affected by several different factors, and the link between the osmoconforming nature of this species and its cold resistance is discussed. Copyright 1997 Academic Press. Copyright 1997Academic Press     

Uronychia transfuga (O. F. Müller, 1786) Stein, 1859 (Ciliophora, Hypotrichia, Uronychiidae): Cortical Structure and Morphogenesis during Division

Morphogenesis of cell division was investigated in Uronychia transfuga utilizing both light microscopy of living and stained specimens and SEM of preserved specimens. The cortical morphogenetic pattern of Uronychia is similar in several respects to that of the members of the family Euplotidae. These features include: the de novo development of the opisthe oral primordium in a subcortical pouch; the development of frontoventral and transverse cirri for both the proter and opisthe from 5 cirral primordia that form de novo within a single latitudinal developmental zone; and the absence of right marginal cirri. The members of the genus Uronychia also show a number of unique characteristics: development of a proter oral primordium that causes partial replacement of the parental adoral zone of oral polykinetids during development of the proter; a large oral membrane that is divided into a right and left component; large caudal cirri that bend to the left; and dorsal kineties comprised of closely set paired-kinetosome kinetids. When compared to the other euplotid-like ciliates, these unique features support the placement of the genus Uronychia in a separate family, Uronychiidae.     

Temporal and spatial distribution of the dinoflagellate Ceratium hirundinella O.F. Müller within a small productive lake

The growth of Ceratium hirundinella in Esthwaite Water, a small productive lake, was investigated during 1975; the horizontal distribution of the alga was studied on four occasions over a 3-week period. Measurements of lake temperature, oxygen concentration, and vertical stratification of Ceratium at close intervals of depth, were also made. Lake population estimates from large samples at many stations were compared with small samples at the regular sampling station. On two occasions the means of these samples were significantly different (P<0·01). On one date, the estimate of Ceratium abundance in the lake from the large sample at many stations was more than twice the value obtained from the sample collected at the regular sampling station. The population of Ceratium was contagiously distributed in all the large samples. On 3 days the horizontal distribution showed an increase in Ceratium numbers towards the windward shore of the lake. Very large accumulations of Ceratium were found in the metalimnion, just above the anaerobic hypolimnion, during late afternoon. Possible mechanisms of horizontal pattern development are considered, based on the measurements of the vertical distribution of Ceratium, and meteorological factors. The ecological consequences for Ceratium of vertical and horizontal movements, and its spatial distribution in the lake, are discussed.     

Some Observations on Cysts and Excystment of an Israel Strain of Podophrya fixa (O. F. Müller, 1786)

SYNOPSIS. A strain of Podophrya fixa (O. F. Müller, 1786) isolated in 1964 from a stagnant pool in the vicinity of Haifa, Israel, was cultivated in mass cultures and in single clones. It produced smooth-walled cysts, and also the previously described ring-walled cysts. The process of excystment, not previously reported, is described here in detail.     

Caractéristiques De La Stomatogenèse Et Des Ultrastructures Corticale Et Buccale Du Cilié Colpodidea Bursaria Truncatella O. F. Müller, 1773

RESUME. Chacun des 45–80 organelles adoraux de Bursaria truncatella O. F. Müller est constitué de 3 rangées de cinétosomes et l'aire buccale droite est couverte de nombreuses doubles rangées de cinétosomes. La stomatogenèse débute par la désorganisation et la résorption des organelles buccaux postérieurs. Puis, il y a désorganisation des rangées parorales de cinétosomes et multiplication des cinétosomes sur l'aire orale droite, en měme temps que sont rompues, selon une ligne oblique, un certain nombre de cinéties somatiques. La prolifération des cinétosomes aux extrémités des cinéties. de part et d'autre de la ligne de rupture, aboutit, d'une part, à la formation d'un champ anarchique qui est le primordium oral droit de l'opisthe, d'autre part, à la formation de nombreux doublets qui constituent chacun le primordium de chaque organelle adoral. Après la séparation des tomites, les cinétosomes de l'aire droite s'ordonnent en doubles rangées et les organelles adoraux se complètent par addition d'une 3ème rangée de cinétosomes. Les cinétosomes somatiques sont jumelés, reliés par 2 desmoses. Les fibres transverses postérieures et les fibres postciliaires forment de longs rubans de microtubules dirigés vers l'arrière et juxtaposés dans les crětes intercinétiennes. Les doubles rangées droites de cinétosomes buccaux sont assimilables à des stichodyades. Les organelles des cinétosomes adoraux portent des rideaux de fibres postciliaires convergents ou divergents. La rangée postérieure de chaque organelle est non ciliée. Par son type de stomatogenèse, par sa structure corticale, par l'ultrastructure des organelles adoraux, Bursaria appartient aux Colpodidea, ce qui suggère des remarques de plusieurs types. SYNOPSIS. In Bursaria truncatella O. F. Müller, each of the 45–80 adoral organelles is composed of 3 rows of kinetosomes, and the right buccal area is covered by many double rows of kinetosomes. Stomatogenesis begins by disorganization and disappearance of the posterior buccal organelles. Next, there is disorganization of the paroral rows of kinetosomes and multiplication of kinetosomes in the right oral area; at the same time, some somatic kineties are disrupted along an oblique line. Multiplication of kinetosomes at the extremities of the kineties, on both sides of the disruption, leads to the formation of an anarchic field which is the right oral primordium of the opisthe and the formation of doublets each of which constitutes an adoral organelle. After the separation of the tomites. the kinetosomes in the right buccal area position themselves, and the adoral organelles are completed by the addition of a 3rd row of kinetosomes. Somatic kineties are formed by successive pairs of ciliated kinetosomes united by 2 desmoses. the long posterior transverse ribbons and the postciliary ribbons extend posteriad, overlapping in the pellicular ridges. Oral rows of kinetosomes on the right can be compared with stichodyads. the adoral kinetosomes have convergent or divergent postciliary ribbons. the posterior row of kinetosomes in each organelle is not ciliated. By the type of stomatogenesis, the cortical ultrastructure, the ultrastructure adoral of its organelles, Bursaria belongs to the Colpodidea.     

Description de Quelques Espèces de Ciliés Hyménostomes des Genres Sathrophilus Corliss, 1960, Cyclidium O. F. Müller, 1786, Histiobalantium Stokes, 1886

RESUME. Les structures buccales de Sathrophilus vernalis Dragesco & Grolière, 1969 sont détaillées. La morphogenèse buccale de l'opisthe, semi-autonome, avec participation du scuticus et d'une cinétie postorale droite, s'accompagne d'une re-constitution de l'appareil buccal du proter. La morphologie buccale de Cyclidium sphagnetorum Šràmek-Hušek, 1949 est comparée à celles de Cyclidium citrullus Cohn, 1865 et Cyclidium glaucoma O. F. Müller, 1786. La stomatogenèse Histiobalantium majus Kahl, 1933 débute par une prolifération du scuticus vers la gauche.
SYNOPSIS. Buccal structures of Sathrophilus vernalis Dragesco & Grolière, 1969 are described. The semiautonomous buccal morphogenesis of the opisthe, involving the participation of the scuticus and the right postoral kinety, is accompanied by the reconstitution of the buccal apparatus of the proter. The buccal structure of Cyclidium sphagnetorum Šràmek-Hušek, 1949 is compared to those of Cyclidium citrullus Cohn, 1865 and Cyclidium glaucoma O. F. Müller, 1786. Stomatogenesis of Histiobalantidium majus Kahl, 1933 starts with a proliferation of the scuticus towards the left.