Brachionus caudatus f. apsteini is a common taxon which has wide distribution in Thai
freshwater habitats . It also has been recorded from Malaysia, India and Japan. This form differs from B. caudatus f. caudatus in having antero-lateral spines . We found two phenotypes of B. caudatus f. apsteini (short and long posteriorspined
forms, Fig. 1) occurring in the same water body. Numerous specimens of the long posterior-spined forms were present in all seasons (summer, rainy and winter) of the year
while a few short posterior-spined forms appeared only in summer and rainy seasons