Fauna of Cladocera (Crustacea: Branchiopoda) of Sabah state of Malaysia, Borneo Island, was evaluated for the first time. Samples from 40 locations were studied, and 31 species of Cladocera were revealed, including three species of Sididae, one species of Daphnidae, one species of Moinidae, four species of Macrothricidae, two species of Ilyocryptidae, and 20 species of Chydoridae. One species of Ilyocryptidae, Ilyocryptus yooni Jeong, Kotov and Lee, 2012, is recorded for Malaysia for the first time, and one more, Anthalona sp., is probably new for science. Of 31 species recorded for Sabah, only three are true planktonic species and 28 are substrate-associated species. Absence of large natural lakes, habitats with most rich cladoceran fauna, can be an important factor limiting diversity of Cladocera in Sabah.
Unlike those in the mainland of Southeast Asia, the Cladocera of the Malay Archipelago has not been intensively studied, except for the state of Sabah in the north-eastern part of the Borneo island. This study aimed to complete the inventory of the Cladocera in Sabah by looking at different types of water bodies including oxbow lakes, small lakes, reservoirs, ponds, ditches and paddy fields. From 32 sites examined, 35 species of cladocerans, nine of which were new records to Sabah, were found from 25 localities. With this new finding, the total number of cladoceran species in Sabah increased to 39 species, including five species of Sididae, four species of Daphniidae, one species of Moinidae, five species of Macrothricidae, two species of Ilyocryptidae, and 22 species of Chydoridae. Only 8 % ( three species) of Sabah cladocerans are true planktonic. This study illustrated that most cladocerans were associated with substrates in the littoral zone and thus appropriate sampling methods should be employed in different microhabitats for comprehensive biodiversity assessment.
Study of Ephemeroporus Frey, 1982 populations from Peninsular Malaysia revealed a new species. Ephemeroporus malaysiaensis sp. nov. is characterized by the presence of four-five large denticles on anal margin of postabdomen instead of two-three, and five distinctive pigmented spots on each valve. Pigmented spots on the valves were never recorded for any species of family Chydoridae. E. malaysiaensis sp. nov. seems to be another endemic Chydoridae species of South-East Asia. E. malaysiaensis sp. nov. is a rare species, associated with emergent macrophytes in the littoral zone of shallow lake. Most of Ephemeroporus populations from Peninsular Malaysia belong to eurybiotic Paleotropical species Ephemeroporus barroisi (Richard, 1984).
A new species of Ovalona Van Damme & Dumont, 2008 (Cladocera: Anomopoda) related to the rare Australian species Ovalona archeri (Sars, 1888), is described from the Mekong Delta, South Vietnam. Ovalona garibiani sp. nov. differs from O. archeri in morphology of antenna, postabdomen, and proportions of setae on thoracic limbs II-III. Both species differ from other species of the genus Ovalona in the postabdomen with a narrow and sparsely spaced group of lateral setulae, the distance between the postanal groups being slightly greater than the width of the group. O. garibiani sp. nov. is a rare phytophilous species, known from a few localities in continental Malaysia, Southern Thailand and Vietnam.
Cladoceran samples from Peninsular Malaysia were collected during four sampling trips: in October 2013, November-December 2014, January-February 2018, and September 2022. More than 50 localities were sampled on each trip, including ditches, canals, rivers, ponds, swamps, lakes, old mining pools, and reservoirs. In these samples, we revealed six species new to Malaysia: two of them are planktonic (Bosmina meridionalis and Bosmina fatalis) and four are substrate-associated (Simocephalus expinosus, Anthalona spinifera, Anthalona vandammei, Karualona serrulata). Both species of the genus Bosmina appear to be recent additions to the local fauna, as this genus was not recorded in Malaysia until the last decade. New records are obtained on three rare local species: Simocephalus mixtus, Streblocerus spinulatus, and Acroperus harpae. The morphology of two uncommon East Asian species, Coronatella acuticostata and Chydorus obscurirostris tasekberae was investigated in detail for the first time. With the new records, the list of valid cladoceran species of Malaysia now consists of 72 species as compared to 62 species reported by Idris (1983) in his monograph. However, more studies are needed to produce an exhaustive final species list of the Malaysian cladocerans.