ABSTRACT

The species Daday (1898) describes as Alona globulosa has been critically studied, based on many populations from tropical and subtropical regions of the world, over its whole geographical range . A new species and a new subspecies are described . Based on the morphological characters of this species group, which are markedly different from those of the genera previously used for this species, namely Alona, Alonella,

The freshwater Cladocera of Sri Lanka has been revised based on the study of over 700 zooplankton samples collected from all habitat types during 1965-1980 . The cladoceran fauna is represented by six families ; members of the families Polyphemidae, Leptodoridae and Holopedidae are absent . The common temperate genus Daphnia is rare .Sixty-two species have been recorded from Sri Lanka . Of these, five are new records . Remarks on a few species are given with illustrations . The distribution of Cladocera in different types of habitats is discussed . The greatest species diversity was found in ponds . The Sri Lankan fauna is numerically and in species diversity typical of tropical cladoceran fauna . It resembles the southern Indian fauna very closely except for the absence in Sri Lanka of the genera Acroperus and Camptocercus .

The morphological relationships of Euryalona orientalis (Daday, 1898) and its related species were studied based on the populations from different parts of the world. The type specimens of Euryalona orientalis and Euryalona occidentalis Sars, 1901 were examined to re-evaluate the taxonomic status of these two species. It was confirmed that E. occidentalis is a synonym of E. orientalis. A detailed description of E. orientalis is provided and a detailed comparison is made with a related species E. fasciculata.

A study of zooplankton samples taken from Parakrama Samudra revealed long-term changes in species composition. However, these changes were probably due to low water levels following a catastrophic cyclone in 1978. Species composition seems to have returned to a stable condition after restoration of high water levels. Seasonal changes in composition and densities of plankton were not marked over a three-years sampling period.

Kurzia longirostris (Daday) from throughout the tropical region was examined, together with a review of all previous records worldwide. It is clear that what was considered K. longirostris consists of two species in the Oriental region. This includes a new species, Kurzia brevilabris sp.nov. It differs from K. longirostris in the head pore configuration, the structure of the labrum, and the arrangement of the submarginal setules along the posteroventral corner of the carapace. A detailed description of the species is given. A detailed redescription of K. longirostris is given based on the types and material from Sri Lanka. The morphological variations observed in different populations of the tropical region are also included in the description.

Males and ephippial females of Dadaya macrops (Daday), a widely distributed tropical cladoceran, are described for the first time together with hitherto unrecorded morphological features of the parthenogenetic female. The postabdomen of the male is unique among chydorids in having only a vestige of the terminal claw. This confirms the validity of this monotypic genus. The material studied comes from Sri Lanka (Ceylon), taken in the neighbourhood of the type locality. Our description provides a detailed morphological record of a population containing all instars of males and females, and both parthenogenetic and ephippial adult females. Type material of parthenogenetic females, the only forms hitherto known, agrees closely with our material. An analysis of the population structure is given.

Based on the study of the type series and material from Sri Lanka, a comprehensive description of Chydorus ventricosus Daday is given including the first description of the male. The detailed morphology of all instars of females and males, population structure, and some biological notes are also provided. This species was considered a tropicopolitan species based on previous records from Asia, America, and Africa. However, a detailed study of populations from a wide area of the Oriental region and material previously designated as Chydorus ventricosus from America and Africa, and a critical review of the literature indicates that it is very probably restricted to the Oriental region. Chydorus ventricosus closely resembles an undetermined number of taxa. Only a detailed study will determine their status. We have compared it with the only two well-described, closely related species. The present study has characterized all stages of Chydorus ventricosus. This will enable accurate diagnosis of this species.