Nikolai M. Korovchinsky

Global diversity of cladocerans (Cladocera; Crustacea) in freshwater

Cladocera is a primarily-freshwater monophyletic group, an important component of the microcrustacean zooplankton. They inhabit most types of continental fresh and saline water habitats, occurring more abundantly in both temporary and permanent stagnant waters. Cladocera is an ancient group of Palaeozoic origin. About 620 species are currently known, but we estimate that the real number of species is 2–4 times higher. A number of currently-recognised widespread species can be expected to harbour extensive cryptic diversity.

How many species of Cladocera are there

An estimation of the number of taxa within families, genera and local faunas of Cladocera reveals that only c. 129 species (17% of all known species) may be considered as sufficiently well described (valid species), and c. 146 as rather well described (fair species) but needing further study using modern methods of investigation. The status of all other species is vague. The families Chydoridae, Daphniidae and Sididae and genera Diaphanosoma, Daphnia, (including Daphniopsis), Megafenestra, Scapholeberis, Eurycercus, Chydorus, Ephemeroporus and Pleuroxus have been comparatively studied best. The largest number of valid species is known from Europe, North America, Australia and South America, and the smallest number from Africa. Presence of large number of vague species of Cladocera negatively affects faunistic, zoogeographic, and ecological studies of continental waters.

The resting eggs of the Ctenopoda (Crustacea: Branchiopoda): a review

The resting eggs of the Ctenopoda have been studied since the second half of the 19th century. By now they are known in 21 species of the group but only in 4 species (Sida crystallina, Diaphanosoma brachyurum, Penilia avistoris and Holopedium gibberum) have they been investigated thoroughly. Gross and internal structure of eggs are characterized by considerable diversity. In general their structure has much in common with resting eggs of the Anostraca, Notostraca, “Conchostraca” and Onychopoda as well as with that of some other remotely related groups of freshwater invertebrates (Rotifera, Hydra). The taxonomic value of resting eggs is discussed. Probably they play a significant role in determining geographical distribution. Waterfowl are the main agent of their dispersal.

Species richness of pelagic Cladocera of large lakes in the eastern hemisphere

The composition of the pelagic cladoceran species assemblages in some large, well-studied, lakes of Europe, Asia and Africa is reviewed based on original and literature data. In general, pelagic cladocerans are taxonomically less well studied than some littoral groups. Only the limnetic members of the family Sididae and some Daphnia have recently been revised, whereas knowledge of species diversity of other Daphniidae (including moinas) and Bosminidae is missing. Future detailed taxonomic studies may lead to considerable changes in understanding of limnetic zooplankton composition.

On the history of studies on cladoceran taxonomy and morphology, with emphasis on early work and causes of insufficient knowledge of the diversity of the group

The long history of cladoceran morphological andtaxonomic studies beginning in the second halfof the 17th century to nowadays is divided into sevensubsequent periods. Each of them is characterized bydomination of specific trends and a noticeableincrease of the number of taxa described. In spite ofthe multitude of studies the taxonomic diversity ofcladocerans, especially at species level, remain to beinsufficiently known. The history of hydrobiology isbriefly reviewed in order to reveal the causes ofthis insufficient knowledge among which historicalfactors and a long domination of an integral approachto studies of continental water bodies are thought tobe most important.

Revision of the Diaphanosoma modigliani – Diaphanosoma dubium species group (Crustacea: Ctenopoda: Sididae), with description of a new species from Tropical Asia

We provide a taxonomic differentiation of species related to Diaphanosoma modigliani Richard s.str., recorded outside its type locality (Lake Toba, Sumatra, Indonesia) for the first time. Diaphanosoma tropicum sp.nov. is described on material from Sri Lanka, Malaysia, Thailand, Philippines and China with analysis of interpopulation morphological variability supplemented by notes on geographical distribution and biology of the species.

Redescription of Diaphanosoma dubium Manuilova, 1964 (Branchiopoda: Ctenopoda: Sididae), and description of a new, related species

The poorly known D. dubium Manuilova is redescribed on extensive material from more than 80 populations from the Russian Far East, Central Asia, Mongolia, China, Japan, Vietnam, the Philippines, Thailand, Malaysia, Bangladesh, India and Sri Lanka. Its morphological variability and geographical distribution are analysed and supplemented by notes on biology. The conspecificity of morphologically different distant populations is discussed. In the northern part of its range, D. dubium was long confused with D. brachyurum or D. leuchtenbergianum, and in the south with D. modigliani. It seems that the recent appearance of D. dubium in fish ponds of Uzbekistan and Kazakhstan was an introduction, together with Far Eastern fish. D. pseudodubium sp.nov., close to but markedly different, is described from two lakes in the lower Amur river system. D. dubium, D. pseudodubium, D. tropicum and D. modigliani s. str. form a group of related species, widely distributed in Eastern and Southern Asia.

Zooplankton of lakes in the spurs of the Putorana Plateau and adjacent territories (North of Krasnoyarsk Krai)

Species composition and parameters of biomass of net plankton were analyzed for four large and 35 small lakes from 10 areas located between 69.5° and 67.5°N and 87° and 92°E that were examined in July–August, 2001 and 2003–2004. In the composition of the first (dominant) and/or second (subdominant) species in the ranged row of the average biomass, the lakes were copepod in 78.8% of cases, in 67.3%, calanoid. The share of biomass of cladocerans in the total biomass of zooplankton exceeded 50% only in 31% of cases. By the frequency of occurrence as dominant or subdominant by biomass the first place is occupied by copepodites calanoid (34.6% of cases), the second, by sexually mature Heterocope appendiculata (26.9%), the third, by copepodites cyclopoid (17.3%), the fourth, by Polyphemus pediculus (15.4%), the fifth, by Acanthodiaptomus denticornis (13.5%), the sixth, by Bosmina cf. longispina (11.5%), the seventh, by Heterocope borealis (9.6%), the eighth, by Daphnia cf. longispina (7.7% of cases). For the first time in the region 14 species of crustacean zooplankton are given. The known range of some species and subspecies (for example, Chydorus biovatus, Camptocercus fennicus, Ophyoxus gracilis kolymensis, Arctodiaptomus acutilobatus, Acanthrodiaptomus tibetanus) is widened owing to the findings in the studied region. The groups of the areas are more similar in terms of zooplankton north to south than east to west; the number of the cladoceran species and the number of cladoceran lakes grew north to south and east to west, which corresponded to the general change of climate towards more mild north to south for similar altitudes and east to west for different altitudes from mountain areas to the low lands. The comparison of the species lists from different northern regions showed that the species diversity (total number of species) of cladocerans and copepods does not change significantly west to east. Distribution of species and changes in the zooplankton structure are discussed from the point of view of possible influence of the global warming.

Review of Sididae (Crustacea: Cladocera: Ctenopoda) of the Pacific Ocean Islands, with description of a new species of Diaphanosoma from West Samoa

Review of the Sididae of the Pacific Ocean islands revealed only three species (Diaphanosoma sarsi s. l., Latonopsis australis s. l., and L. brehmi) so far known from New Caledonia, Vanuatu (New Hebrides), Fiji, Guam Island, and Hawaii. Study of museum and other additional material made it possible to describe a new species, D. samoaensis, from West Samoa, the first record of an endemic sidid on a small ocean island. Its mode of speciation is discussed.

Description of two new species of Diaphanosoma Fischer, 1850 (Crustacea, Branchiopoda, Sididae) from the United States and Canada and species richness of the genus in North America

Investigation of a small number of samples with representatives of the genus Diaphanosoma from the cladoceran collection of the National Museum of Natural History, Smithsonian Institution (Washington, D.C., U.S.A.) has revealed two new species, D. freyi and D. heberti, from Louisiana–Missouri and Newfoundland, respectively. The former looks like one of the most primitive species of the genus. Two other species, D. fluviatile and D. brevireme, are recorded from the southern United States for the first time. Members of the D. brachyurum and D. birgei species groups, which are morphologically variable and need further detailed investigations, were represented in the bulk of the material studied. The species richness of the genus in North America appears to be high and its composition is obviously complex but remains little studied.