On the Life History ofTigriopus japonicusMORI (Copepoda)

Abstract

This species is the neritic animal in warm waters, especially a large number of the species appear in the tide pool in spring to summer season. The species has the adaptability to the environment, namely, the species is eurythermal and euryhaline organism.
Each nauplius stage ofT. japonicuschanged into the next stage in 18 to 20 hours. After hatching the nauplius developed into the copepodite stage in 3 to 5 days. The nauplius is disk-shaped in outline. A small antennule is 3-segmented. The antenna and mandible are the assistant oral organs for foods rather than swimming ones. On the antenna the coxa has the process with the strong cutting edge, the basipodite is extremely small, the long endopodite has a hook and a seta ventrally, and a hook, a seta and a spine terminally, and the long exopodite has the setae of which the number was changed according to the stage. On the mandible the coxa with a seta is a bulge. The endopodite is a small mound, on this mound there are a strong hook and a few setae which were changed according to the stage. The exopodite has a ventral seta and a small and a long thick terminal setae. The caudal appendages are rudimentary. The maxillule first appears as a seta on the 2nd stage.
On the copedite stage ofT. japonicusthe segment of body is short. The cephalothoracic segments are indistinguishable from the abdominal segments. It is the character of Harpacticoida that the antennules are small. On this copedodite there are 6 stages as in the nauplius, but the last stage is the adult stage. The 1st and the 2nd stages changed into the next stage in 18 to 20 hours as in the nauplius. The 3rd to the 5th stages changed into the next stage within 1 day. After hatching the nauplius developed into the adult by 10 days. The period of each stage fluctuates according to the amount of foods which were supplied to the animal. On the starved condition the development of this animal does not occur by any means.
The most of male have mated with the adult female, but some of them mated with the earlier stage, especially the 2nd copepodite stage female. The female which developed into the adult produced the first brood in a few minutes to 3 days. A period of the adult stage is assumed 1 to 2 months.
A female produced 5-10 broods. After hatching of the brood the next brood was bred in a few minutes to 1 day. The female which was 0.9 mm in the mean length produced 30 eggs per a brood.