Description de Falklandia gen.n. de I'Ocean Austral et définition des Lysianassoidea uristidiens (Crustacea, Amphipoda)

The revision of the antarctic–subantarctic species Orchomenopsis reducta Schellenberg, 1931, has led to its attribution to a new, highly apomorphic genus: Falklandia gen.n. A new definition of the uristid group is given and Falklandia with 36 other lysianassoid genera are attributed to this supposedly monophyletic group.     

Antigenic Heterogeneity of Human IgD Immunoglobulins

SUBCLASSES of the three major classes of human immunoglobulins, IgG, IgA and IgM, are recognized: four of IgG are well defined^1,2 and at least two of IgA^3–5 and two of IgM^6,7 have been demonstrated. This communication presents evidence for the existence of an antigenic heterogeneity in the heavy chains of IgD, which may also be indicative of subclasses within this class of immunoglobulin.     

Taxonomy of the Houbara Bustard Chlamydotis undulata subspecies considered on the basis of sexual display and genetic divergence

The Houbara Bustard Chlamydotis undulata is a polytypic species with three subspecies classified according size, colour and distribution: C. u. undulata, C. u. fuertaventurae and C. u. macqueenii. A comparative study of the male display behaviour of these three subspecies has shown similarities between C. u. undulata and C. u. fuertaventurae , whereas appreciable differences exist in the visual and auditory aspects of the display between C. u. undulata and C. u. macqueenii. These observations make the current taxonomy of Houbara Bustard questionable, particularly in view of the major importance of the sexual display in bird speciation processes. Furthermore, DNA analysis of the cytochrome b gene indicates the existence of a significant differentiation between the C. u. undulata and C. u. macqueenii populations. These findings indicate the need for a revision of the taxonomy of genus Chlamydotis which should separate the macqueenii and undulata populations at species rank. Until further investigations are completed, C. u. fuertaventurae should be kept as a subspecies of undulata since the courtship display is alike in both populations.     

Pyura lignosa (s. s.), a Pacific ascidian from Central America, with descriptions of species confused under this name

New specimens from the Pacific coast of Panama provide the opportunity to redescribe Pyura lignosa Michaelsen, 1908. The status of this species and of three other similar pyurids ( P. vannamei nomen novum, P. cadamostoi sp. nov., and P. shiinoi Tokioka, 1949) is examined, and all four species are identified, described, and compared.     

New highlights about the enigmatic marine snake Palaeophis maghrebianus (Palaeophiidae; Palaeophiinae) from the Ypresian (Lower Eocene) phosphates of Morocco

Abstract: Palaeophis maghrebianus belongs to the Palaeophiinae (Palaeophiidae). This snake subfamily is relatively poorly known, and it is mainly represented by disarticulated vertebrae and ribs and by a few vertebral segments. Its intracolumnar variability remains also poorly understood. The discovery of new isolated vertebrae and vertebral segments of Palaeophis maghrebianus in the Ypresian (Lower Eocene) Phosphates of Morocco enables us to provide a more detailed diagnosis of this species and to describe its intracolumnar variability. Moreover, the new material reveals that this species could reach gigantic size being, with Palaeophis colossaeus, one of the two longer palaeophiids. The microanatomical and histological analysis of some vertebrae illustrating diverse positions along the vertebral column reveals the presence of osteosclerosis, especially in the anterior and mid‐precloacal regions. The occurrence of this osseous specialization implies a role in buoyancy and body trim control in this taxon, which is considered a shallow marine dweller based on its anatomical features and geological data. Palaeophis maghrebianus also displays a dense vascular network suggesting a growth speed, and thus a metabolic rate, much higher than in the biggest extant snakes.     

Deterination of Effective Partition Coefficients of Alkali Chlorides by Measurements of Concentration Potential across the Nitella flexilis (L.) Ag. Isolated Cell Wall

We report a study in which we estimate by means of non-equilibriumprocesses the value of an effective partition coefficient, x,a parameter that we use to take into account the non-ideal behaviourof the electrolyte of the external medium in the cell wall space.This parameter is defined by the ratio of the salt partitioncoefficient to the activity of the non-diffusing charges. Tothat purpose, concentration potential in NaCl, LiCI and CuCl₂solutions was measured across an isolated cell wall of Nitellaflexilis at different pH. No significant difference appearedbetween the potential values measured in the presence of NaClor LiCl (pH 5.5, 4.0 and 3.0). At pH 3.0, in CuCl₂ solutions,the Nitella wall behaved as an uncharged membrane. Two methods—high concentrations and least-squares approximation-wereused to calculate from these results the value of the effectivepartition coefficient. Both gave similar values of x At a givenpH, the values of x are independent of the concentration ofthe external medium over a large range of concentration ratios.The activity of the exchange sites was estimated by the experimentallydetermined fraction of absorbed monovalent cations. The ionicconcentrations in the wall space were calculated at pH 5.5 and3.0 by introducing the values of x in the relations which correlatethem to the ionic concentrations in the wall for that givenvalue of the activity of the carboxylate sites. From their values,it appears that the negative fixed charges of the wall werefunctionally shaded by the condensation of a part of the adsorbedmonovalent cations. The activity of the former was, therefore,reduced to a value considerably lower than that estimated bythe cationic exchange capacity during equilibrium processes. Key words: Nitella flexilis (L.) Ag., cell wall, concentration potential, partition coefficient, ion condensation     

Revision of the genus Acrochordiceras Hyatt, 1877 (Ammonoidea,Middle Triassic): morphology,biometry, biostratigraphy and intra‐specific variability

Abstract: The family Acrochordiceratidae Arthaber, 1911 ranges in age from latest Spathian to the middle/late Anisian boundary, and it represents a major component of ammonoid faunas during that time. The middle Anisian genus Acrochordiceras Hyatt, 1877 is the most widespread taxon of the family and occurs abundantly worldwide within the low paleolatitude belt. However, there is a profusion of species names available for Acrochordiceras. This excessive diversity at the species level essentially results from the fact that sufficiently large samples were not available, thus leading to a typological approach to its taxonomy. Based on new extensive collections obtained from the Anisian (Middle Triassic) Fossil Hill Member (Star Peak Group, north‐west Nevada) for which a high resolution biostratigraphic frame is available, the taxonomy and biostratigraphy of the genus Acrochordiceras Hyatt, 1877 is herein revised with respect to its intra‐specific variation. Morphological and biometric studies (c. 550 bedrock‐controlled specimens were measured) show that only one species occurs in each stratigraphic level. Continuous ranges of intra‐specific variation of studied specimens enable us to synonymize Haydenites Diener, 1907, Silesiacrochordiceras Diener, 1916 and Epacrochordiceras Spath, 1934 with Acrochordiceras Hyatt, 1877. Three stratigraphically successive species are herein recognized in the low paleolatitude middle Anisian faunas from Nevada: A. hatschekii (Diener, 1907), A. hyatti Meek, 1877 and A. carolinae Mojsisovics, 1882. Moreover, an assessment of intra‐specific variation of the adult size range does not support recognition of a dimorphic pair (Acrochordiceras and Epacrochordiceras) as previously suggested by other workers (Epacrochordiceras is the compressed and weakly ornamented end‐member variant of Acrochordiceras). The successive middle Anisian species of Acrochordiceras form an anagenetic lineage characterized by increasing involution, adult size and intra‐specific variation. This taxonomic revision based on new bedrock‐controlled collections is thus an important prerequisite before studying the evolution of the group.