A NEW SPINICAUDATAN GENUS (CRUSTACEA: ‘CONCHOSTRACA’) FROM THE LATE CRETACEOUS OF MADAGASCAR

Abstract: A new spinicaudatan genus and species, Ethmosestheria mahajangaensis gen. et sp. nov., is described from the Anembalemba Member (Upper Cretaceous, Maastrichtian) of the Maevarano Formation, Mahajanga Basin, Madagascar. This is the first spinicaudatan reported from the post‐Triassic Mesozoic of Madagascar. The new species is assigned to the family Antronestheriidae based on the cavernous or sievelike ornamentation on the carapace. Of well‐documented Mesozoic spinicaudatan genera, Ethmosestheria mahajangaensis is most closely related to Antronestheria Chen and Hudson from the Great Estuarine Group (Jurassic) of Scotland. However, relatively poor documentation of the ornamentation of most Gondwanan Mesozoic spinicaudatan species precludes detailed comparison among taxa. Ethmosestheria mahajangaensis exhibits ontogenetic trends in carapace growth: a change in carapace outline from subcircular/subelliptical to elliptical, and from very wide juvenile growth bands to narrow adult growth bands. Ornamentation style, however, does not vary with ontogeny. Ethmosestheria mahajangaensis individuals lived in temporary pools in a broad channel‐belt system within a semiarid environment; preserved desiccation structures on carapaces indicate seasonal drying out of pools within the river system. Specimens of Ethmosestheria mahajangaensis are preserved with exquisite detail in debris flow deposits; these are the first spinicaudatans reported from debris flow deposits. These deposits also contain a varied vertebrate fauna, including dinosaurs, crocodyliforms, turtles, and frogs. Rapid entombment of the spinicaudatan carapaces likely promoted early fossil diagenesis leading to highly detailed preservation.     

A new species of Cyzicidae (Crustacea: Conchostraca) from Iraq

A new species of Conchostraca, Eocyzicus mesopotamiensis sp. nov., from a small pond in Iraq is described and illustrated. The account includes structural details and means of recognition. Information on the habitat is also given.     

原狭蚌虫属一新种（鳃足纲：介甲目）

作者于1987年6月自山东省兖州县淡水养殖试验场鱼池中发现原狭蚌虫属的一个新种——兖州原狭蚌虫Eoleptestheria yanchowensis sp.nov.作者对新种的形态特征进行了详细描述,并与中国原狭蚌虫Eoleptestheria chinensis Daday 1923,及东平原狭蚌虫Eoleptestheria dongpingensis Hu 1987。作了比较。     

Review of Colombian Conchostraca (Crustacea) — morphotaxonomic aspects

This paper presents an overview of the current knowledge about species diversity and morphological taxonomy of the Colombian conchostracan fauna. Relationships among morphological variability, reproduction biology and environmental conditions are stressed. The Colombian fauna includes 12 species in five families: Limnadiidae Sars, 1896; Leptestheriidae Daday, 1915; Cyclestheriidae G. O. Sars, 1899; Metalimnadiidae Strakraba, 1965; and Lynceidae Stebbing, 1902. No member of the families, Cyzicidae Stebbing, 1910, or Imnadiidae Botnariuc & Orghidan 1941 have been found in Columbia. Morphology depends on developmental stage and on the modulating effects of environmental conditions. Extremely high temperatures may lead to specimens with neotenic features inEulimnadia magdalenensis Roessler, 1990.     

SEM investigations of the larval development of Imnadia yeyetta and Leptestheria dahalacensis (Crustacea: Branchiopoda: Spinicaudata)

This paper presents a SEM documentation of the larval development of the two most abundant Austrian conchostracan species, Imnadia yeyetta (Limnadiidae) and Leptestheria dahalacensis (Leptestheriidae). As in several previously examined spinicaudatan species, five larval stages were documented: Nauplius 1, Nauplius 2, Metanauplius, Peltatulus, and Heilophore. Additionally, three postlarval stages of L. dahalacensis and the first larval instars of Eoleptestheria ticinensis and Limnadia lenticularis are shown and compared with the examined stages. Species identification of conchostracan larval stages is possible by using surface structures, and using SEM methods, except for L. lenticularis which can be identified more easily on the characteristic shape of the labrum.     

新疆中二叠世叶肢介化石

描述新疆阜康三工河剖面芦草沟组的叶肢介石２科３属４种（其中２新种）和鄯善照壁山剖面“照壁山组“的叶肢介化石２科４属５种,时代均为中二叠世。     

Reinvestigation of conchostracans (Crustacea: Branchiopoda) from the Permian–Triassic transition in Southwest China

Sedimentary deposits of the Permian–Triassic transition are well-exposed in numerous outcrops of South China. Depending on the palaeogeographic positions of the sections, their lithofacies vary from fully marine, shallow marine, lagoonal, lacustrine, and fluvial to alluvial. In the present study, conchostracans (Crustacea: Branchiopoda) were newly collected from the continental deposits of the Kayitou and Jialingjiang formations around the Kangdian Highland elevated by the Emeishan Basalt in the southern Sichuan, western Guizhou, and northeastern Yunnan provinces. The conchostracan fauna of the Kayitou Formation is composed of Pseudestheria chatangensis, Euestheria fuyuanensis, and Euestheria sp. aff. E. gutta. These species occur in varying lithofacies types of different sections. In particular, the late Permian Pseudestheria chatangensis occurs in grey siltstones interbedded with pebbly sandstones, which are interpreted as lacustrine deposits. Euestheria fuyuanensis and Euestheria sp. aff. E. gutta were obtained from yellowish to greenish–grey clay- and siltstones, interpreted as coastal plain deposits. In comparison to other regions, occurrences of Euestheria gutta are indicative of an early Induan to Olenekian (Early Triassic) age. The fossil record of Euestheria fuyuanensis is so far restricted to a few occurrences in the Kayitou Formation of Southwest China and, therefore, using this species for long-distance biostratigraphic correlation requires further investigation. The distribution of late Permian pseudestheriid and Early Triassic euestheriid species in the respective sections possibly depends on the local lithofacies and, therefore, a diachronous age of the Kayitou Formation within the study area can be assumed. Additionally, Magniestheria sp. aff. M. mangaliensis and Magniestheria sp. aff. M. subcircularis were recorded in the Jialingjiang Formation, which represents a lithostratigraphic unit considered as late Early Triassic (Olenekian). Further investigations of both taxonomy and the real stratigraphic ranges of the conchostracan species as well as cross-correlations with other age data are recommended, in order to better constrain the position of the Permian–Triassic boundary and the specific timing of the terrestrial end-Permian mass extinction in continental deposits of Southwest China.     

Fine structure and function of ocelli and sagittocysts of acoel flatworms

We studied the taxonomy and distribution of the Conchostraca in Yugoslavia. A diverse fauna occurs in the country. However, the systematics of this group is still incomplete and has many problems. There is considerable variability of morphological characters. By a comparative-morphological analysis of the populations found, we re-evaluated the taxonomic significance of a series of structural characters, and offer comments on the results.In Yugoslavia four families were found: Cyzicidae Stebbing, 1910; Limnadiidae Burmeister, 1843; Imnadiidae Botnariuc & Orghidan, 1941 and Leptestheriidae Daday, 1923, with a present total of 8 species and 4 subspecies. Within the genus Imnadia Hertzog, 1935, three new species were found: Imnadia cristata Marinek, 1972; Imnadia banatica Marinek & Valvajter, 1982 and Imnadia panonica Marinek & Petrov, 1984. Within the genus Eoleptestheria Daday, 1923, the species Eoleptestheria spinosa Marinek, 1978, with four distinct subspecies was discovered.     

Age-influenced morphological changes inLeptestheria saetosa Marinček et Petrov, 1992 (Conchostraca,Crustacea)

Morphological changes during the process of ageing ofLeptestheria saetosa Marinek et Petrov, 1992 were observed. It was established thet the greatest number of analysed characteristics change intensively after sexual maturation. These changes continue throughout the entire life, although they are very slow in old specimens. Such a large number of changes brings about considerable morphological differences between adult specimens of different age.     

INBREEDING DEPRESSION IN A SELF-COMPATIBLE,ANDRODIOECIOUS CRUSTACEAN,EULIMNADIA TEXANA

The observation that offspring produced by the mating of close relatives are often less fit than those produced by matings between unrelated individuals (i.e., inbreeding depression) has commonly been explained in terms of the increased probability of expressing deleterious recessive alleles among inbred offspring (the partial dominance model). This model predicts that inbreeding depression should be limited in regularly inbreeding populations because the deleterious alleles that cause inbreeding depression (i.e., the genetic load) should be purged by regularly exposing these alleles to natural selection. We indirectly test the partial dominance model using four highly inbred populations of an androdioecious crustacean, the clam shrimp Eulimnadia texana. These shrimp are comprised of males and hermaphrodites, the latter capable of either self-fertilizing or mating with a male (i.e., outcrossing between hermaphrodites is impossible). Hermaphrodites are further subdivided into monogenics (produced via self-fertilization) and amphigenics (produced via self-fertilization or outcrossing). Electrophoretic evidence suggests significant differences in heterozygosity among populations, but that selfing rates were not statistically different (average s = 0.67). Additional electrophoretic analyses reveal that three previously described sex-linked loci (Fum, Idh-1, and Idh-2) are all tightly linked to each other, with crossing over on the order of 1% per generation. Although selfing rates are clearly high, we present evidence that early inbreeding depression (hatching rates, juvenile survival, and age at sexual maturity) exists in all four populations. For all of these factors, inbreeding depression was inferred by the positive correlation of multilocus heterozygosity and fitness. Cumulative inbreeding depression (8) is between 0.41 and 0.47 across all populations, which appears to be too low to limit the effects of purging via identity disequilibrium. Instead, we suggest that the maintenance of inbreeding depression in these populations is due to the observed linkage group, which we suggest contains a large number of genes including many related to fitness. Segregation of such a large linkage group would explain our observations of the predominance of amphigenic hermaphrodites in our field samples and of survival differences between monogenics and amphigenics within selfed clutches. We propose that a modified form of the overdominance model for inbreeding depression operating at the level of linkage groups maintains the observed levels of inbreeding depression in these populations even in the face of high rates of selfing.