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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 3061

Umezawa Shun-ichi; [Some observations on the Habit of a Bdelloid Rotifer, Philodina roseola]. Zoological Magazine (Dobutsugaku Zasshi) 61(7):201-204, 1952

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The common rotifer, Philodina roseola, upon observation of the species, can be kept alive in watch glass as long as sixty-six days -generally forty-five days on the average- on unicellular alga, Colurella ellipsoidea. The fully grown animal, when extended, measures from 0.35 to 0.40 mm in length, and newly hatched young, about 0.12 mm. The body tint is usually colorless or gray, but sometimes pink, regardless of the color of food intaken. This is somewhat in contrast to American species, where it has been determined that the redish color appears to result from food alga, Spaehrella lacustris. The external cuticle is distinctly thicker in the trunk than elsewhere, and this portion strains well with a diluted solution of methylene blue. However, contrary to Jacobs' observation, a positive, instead of negative, phototropism is frequently observed, except in the aged animals. The animal begins to lay parthenogenetic eggs three of four days after hatching and while still in the growing stage, and lay from one or two and sometimes three or four eggs in a day. The total number of eggs from a single female, over her lifetime, is about forty on the average. From the very beginning, the behavior of the young is very similar to that of the adult. Even when placed in redistilled water, the animal can live without food and the life span is shortened somewhat from that of normal life, but the young grows considerably slower, and egg-laying is delayed from eight to sixteen days after hatching, and only three to eight eggs are produced in one generation. The eggs, however, hatch two or three days as in normal environment. In an experiment using redistilled water, one egg was found to hatch within the body cavity of the mother.