A QUANTITATIVE ANALYSIS OF THE ANNUAL TESTICULAR CYCLE OF THE BRITTLE-STAR AMPHIPHOLIS KOCHII BY MEANS OF AUTORADIOGRAPHIC INVESTIGATION

¹ Zoological Institute, Faculty of Science, Hokkaido University, Sapporo 060, Japan

This paper concerns the annual testicular cycle of the brittle-star Amphipholis kochii (Echinodermata: Ophiuroidea). An autoradiographic study was applied for analysis of the seasonal changes in the number of spermatogenic cells, the duration of spermatogenesis and the spermatocyte production rate. The annual testicular cycle can be divided into five phases; spermatogenesis occurs during phases 2 to 4 (November to June). Spermatogenesis during phases 3 and 4 (March to June) was sensitive to the sea water temperature as an external environment, while that during phase 2 (November to February) was insensitive to it. The water temperature directly controls the speed of the later phase of spermatogenesis (from spermatocyte to spermatozoon), but it is not able to control the spermatocyte production rate. It is therefore suggested that the water temperature plays an important role in spermatogenesis during phases 3 and 4 by controlling the speed of the later phase of spermatogenesis, and that other environmental factor(s) controlling the spermatocyte production rate are likely to be important to spermatogenesis during phase 2.