The terrestrial isopods (Crustacea) of Aldabra

Among a collection of terrestrial isopods from Aldabra were 13 species, six of which are new: Littorophiloscia aldabrana, Philoscina insularis, Trichorhina triocellata, Nagurus kensleyi, Pseudodiploexochus cuspidatus and Venezillo pseudoparvus. Alloniscus pigmentatus Budde-Lund and Tura angusta Budde-Lund are re-described and figured. The taxonomy of six species of Alloniscus Dana from the Indian Ocean is discussed and Alloniscus nacreus Collinge from Madagascar is illustrated. The species Armadillo parvus Budde-Lund and Sphaerillo collaris Budde-Lund are transferred to the genus Venezillo Verhoeff. The distribution of all the species is given together with the composition of the oniscidean fauna of Aldabra.     

Variabilité biochimique et génétique de Sphaeroma ghigii,S. hookeri et S. serratum. Comparaison interspécifique

Total proteins, esterases and phosphatases in Sphaeroma ghigii, S. hookeri and S. serratum (Crustacea: Isopoda Flabellifera) were compared by electrophoresis on polyacrylamide gels. Interspecific variations were found which may be useful in taxonomic problems. On the one hand, there are a number of protein and enzyme fractions in each species which differ from each other as well as species specific patterns. On the other hand, the results show some molecular homology which may be interpreted at the phyletic level. Vavilov's law of homologous variation indicates that the interspecific distance between Sphaeroma hookeri and S. ghigii is smaller than between these two species and S. serratum.     

Variabilité biochimique et génétique de Sphaeroma ghigii,S. hookeri et S. serratum. Variations intraspécifiques

Electrophoresis on polyacrylamide gel of enzymes (esterases, phosphatases) and total proteins of Sphaeroma ghigii, S. hookeri and S. serratum shows the existence of important intraspecific variability. Esterases, alkaline phosphatases and major low ionic strength extractable proteins also demonstrate quantitative and qualitative differences between individuals; these differences are the expression of protein and enzyme polymorphism. Some of these variations represent sexual differences which are an expression of a biochemical sexual dimorphism that appears particularly in esterases and phosphatases. Among males, this variability leads to the delineation of several biochemical phenotypes and gives an insight into the genetic variability of populations based on the protein composition of organisms. Taking into consideration the ecological characteristics of the various species of genus Sphaeroma, this polymorphism provides a source of information on ecophysiological relations at the level of proteins and enzymes, that may lead to a better understanding of intraspecific variability.     

Effects of group size on aggregation against desiccation in woodlice (Isopoda: Oniscidea)

Aggregation in terrestrial isopods, a behaviour that results in the formation of dense clusters, is readily accepted as a mechanism of resistance to desiccation. Thus, aggregation is considered to be an adaptation to terrestrial life in this fully terrestrial suborder of crustaceans. In the present study of Porcellio scaber Latreille, a cosmopolitan species, individual water loss is investigated experimentally as a function of the size of the aggregates and, for the first time, over a large range of group sizes (groups of 1, 10, 20, 40, 60, 80 and 100 individuals). From the perspective of an isolated individual, aggregation behaviour is effective in reducing the rate of water loss whatever the group size, and reduces the individual water loss rate by more than half in large groups. However, the water loss rate of an individual follows a power law according to group size. Accordingly, if the addition of individuals to small groups strongly reduces the water losses per individual, adding individuals to large groups only slightly reduces the individual water losses. Thus, the successful reduction of the water loss rate by this aggregation behaviour is confirmed, although only up to a certain limit, particularly if the number of individuals per aggregate exceeds 50–60 under the experimental conditions used in the present study. Moreover, the individual surface area exposed to the air, as a function of group size, follows a similar pattern (i.e. a similar power law). Thus, a geometrical explanation is proposed for the nonlinear water losses in woodlice aggregates. These results are discussed in relation to the group sizes observed both in the laboratory and the field.     

Munnogonium affinissp. n.: A New Species of Isopod (Asellota: Paramunnidae) from the Coast of Korea,Sea of Japan

The new species Munnogonium affinisfrom the coast of Korea (the Sea of Japan) is described. This is the first record of the genus Munnogoniumfrom the western Pacific. The new species differs considerably from the four eastern Pacific American species of this genus and is most similar to M. maltiniifrom the Mediterranean Sea.