STUDIES ON THE REPRODUCTION OF THREE SPECIES OF PEROPHORA (ASCIDIACEA)

¹ Department of Biology, Faculty of Education, Gunma University, Maebashi, Gunma 371, Japan
² Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka 415, Japan

The breeding season is summer for Perophora formosana and P. sagamiensis, and winter for P. japonica. In all species, the gonads lie on the left side within the first intestinal loop. Eggs at the bottom of the ovary mature first. Mature eggs are ovulated into the postero-dorsal corner of the right peribranchial cavity, where they gain access to the brood pouch. In P. sagamiensis, the branchial basket and digestive tract of a zooid disintegrate at the onset of brooding, and after sexual reproduction the whole zooid is resorbed. Very often, such degenerating zooids are replaced by new zooids budded from the basal stolon.

A new mode of asexual reproduction, termed "terminal budding," was found in P. japonica. The distal end of a stolon rises up off the substratum and develops into a discoidal stellate reproductive body which is gorged with granular amoebocytes. This terminal bud is separated from the colony, then is carried away by water currents and adheres to a new substratum, on which it elongates stolons to found a new colony. Terminal budding can coexist with ordinary subterminal budding in the same stolon, but it is suppressed by sexual reproduction.

P. formosana is considered more primitive than the other two species.