Abstract: The features of two physiological types of eggs laid by three species of Tortanus incubated in laboratory were observed during Jan., 1986 to Sep., 1987. It is shown that the eggs are covered by semitransparent case, and only T.derjuginii can lay a certain amount of non-viable eggs without case. In T. derjuginii, eggs with narrower case (≤15μm) and corrugating regularly are subitaneous ones, and those with wider case and corrugating irregularly are diapause ones. The viability of diapause eggs increases significantly with increasing case width. There is no morphological differentiation between subitaneous and diapause eggs in T.forcipatus, and it is noteworthy that no diapause egg in T.dextrilobatus has been occurred. It is suggested that the complicated variation in egg features of Tortanus might be attributed to the population genetic characteristics of producing two physiological types of eggs. Experimental result shows that the diameter and case width of eggs laid by T.dextrilobatus females collected seasonally from Xiamen waters are negatively and positively correlated with temperature respectively, after rearing the females under the laboratory condition for 12 hours and 6 days. It is suggested that the seasonal variation in a short period of 6 days could demonstrate the acclimation of Tortanus to the seasonal temperature fluctuating.

Key words: Tortanus, Egg feature, Diapause eggs, Hatching rate, Seasonal variation, Temperature effect