浮游性魚卵

The present paper, the seventh of the series of the pelagic fish eggs from Japanese waters, contains the figures and descriptions of 5 species belonging to the suborders Chaetodontina, Balistina and Ostraciontina, as well as the matured egg of a single species belonging to Ostraciontina. Chaetodontina. Chaetodontoplus septentrionalis (Temminck et Schlegel) is reported by Fujita and Mito (1960), and Acanthurus triostegus sandvicensis (Linne) by Randall (1961). The eggs are globular, 0.66-0.88 mm in diameter, containing a single oil globule measuring 0.15-0.20 mm in diameter. The egg membrane is smooth, without any conspicuous structure, and the perivitelline space narrow. The yolk is segmented in C. septentrionalis and not segmented in A. triostegus sandvicensis. Only the melanophores develop in the egg. The oil globule of the newly hatched larva is situated in the posterior part of the yolk. The number of myotomes of the hatched larva is 25-27 in C. septentrionalis and 22 in A. triostegus sandvicensis. Balistina. Triacanthus brevirostris Temminck et Schlegel is reported by Ohshima and Nakamura (1941). The egg is globular, 0.78 mm in diameter, lacking the oil globule. The egg membrane is smooth, without any conspicuous structure, the yolk not segmented, and the perivitelline space narrow. During the course of the egg development melanophores and orange-red pigment-cells appear on the embryonal body. The number of myotomes of the hatched larva is about 24. Other members of this suborder of Japanese waters beget demersal adhesive eggs. Ostraciontina. The egg and larval developmet of Ostraciontina Nos. 1 and 2, and the matured ovarian egg of Rhinesomus concatenatus (Bloch et Schneider) are known from southern Japan. These eggs are globular, 1.40-1.96 mm in diameter, containing 4-29 aggregating yellow oil globules measuring 0.02-0.20 mm in diameter. The egg membrane is somewhat thick, light brown in color, the yolk not segmented, the perivitelline space narrow. A thick membranous fold enclosing the head, trunk and the yolk develops in the egg. The hatched larva is robust, having 18-19 myotomes. Head and trunk are enclosed in the thick membranous fold, seemingly the rudiment of the future carapace. Dorsal, anal and pectoral fin rays appear before the consumption of yolk in Ostraciontina No. 2.