浮遊性魚卵

In the previous paper the author gave the keys to the pelagic fish eggs and hatched larvae found in the adjacent waters of Japan. For the convenience of the usage of the keys, the figures and descriptions of the egg development and hatched larvae of identifiable species will be given in the present and following papers of this series, excepting the figures of some species which the author could not observe. In the present series are contained 48 species belonging to the orders or suborders Clupeina, Chanina, Stomiatina, Myctophida, Anguillida, Belonida and Syngnathida. The general characteristics of the pelagic eggs and hatched larvae belonging to the above mentioned orders or suborders are as follows : Clupeina. Konosirus punctatus (Temminck et Schlegel), Anodontostoma cIacunda (Buchanan-Hamilton), Etrumeus micropus (Temminck et Schlegel), Sardinops melanosticta (Temminck et Schlegel), Ilisha elongata (Bennet), Engraulis japonica (Houttuyn), Stolephorus zollingeri (Bleeker), S. indicus (Van Hasselt), Thrissa mystax (Bloch et Snyder), Setipinna taty (Cuvier et Valenciennes), Coilia rnystus (Linne), Chirocentrus dorab (Forskal) and C. hypselosoma Bleeker are known from Japanese waters as well as from the Java Sea. The shape of the egg is ellipsoidal in the species belonging to the subfamily Stolephorinac and globular in other species. The diameter of the egg ranges 0.7-2.5 mm. The perivitelline space is wide or narrow. The egg membrane of most of the species is smooth, without any conspicuous structure or glistening, but some species have a minute appendage or hexagonal mesh structure on the egg membrane. The yolk is segmented as far as known. The oil globule is absent or present. The hatched larva is elongate, having more than 40 myotomes and the anus is situated far backwards. During the course of the egg and larval development only the melanophores appear. Chanina. C hanos chanos (Forskal) is known from the Java Sea. The egg and hatched larva are quite similar to those of clupeid fishes. Stomiatina. Maurolicus japonicus Ishikawa and Chauliodus sloani Schneider are known from Japanese waters. The egg of M. japonicus is globular and coated with a confetto like gelatinous substance, measuring 1.29-1.82 mm in diameter including the envelope and 0.87-1.17 mm without the envelope. The perivitelline space is narrow. The yolk is roughly segmented and contains an oil globule measuring 0.22-0.28 mm in diameter. The egg of C. sloani is large, measuring 2.04-2.52 mm in diameter, the perivitelline space being wide. The yolk is 1.40- 1.52 mm in diameter, segmented and without oil globule. During the course of egg development no pigment appears in M. japonicus, but in C. sloani about 10 dendritic melanophores appear in the caudal marginal fin. The number of myotomes of hatched larva is 31-37 in M. japonicus and 58-61 in C. sloani. Myctophida. Eight species belonging to the family Synodontidae, Harpodon nehereus (Hamilton-Buchanan) and 2 species probably belonging to this order are known from Japanese waters and the Java Sea. The egg of Synodontidae is globular, measuring 1.0-1.3 mm in diameter. The perivitelline space is narrow. The yolk is not segmented, without oil globule. The egg membrane is something thick and with hexagonal mesh structure, measuring 0.03-0.05 mm in diameter of the mesh in Synodus variegatus (Lacepede), Trachinocephalus myops (Schneider), Sauricla undosquamis (Richardson), S. tumbil (Bloch) and 2 other species probably belonging to this family, but it is thin, smooth without any conspicuous structure in Saurida elongata (Temminck et Schlegel) and closely related to 2 other species. The hatched larva is more or less elongate with 49-66 myotomes and the anus is situated far backwards or near the middle of the body. During the course of the egg and larval development only the melanophores appear, and they late unite into 3-5 in number and settle themselves near the ventral median line. The egg of 2 species seemingly belong to this order (Myctophida No. 1, 2) is globular, measuring 1.12-1.37 mm in diameter, and bears numerous short appendages on the egg membrane, about 85-90 or 200-250 in hemisphere respectively. The perivitelline space is narrow. The yolk is not segmented, containing 2-10 oil globules in the early developmental stage, but they unite into a single globule measuring 0.21-0.27 mm during the course of the egg development. Melanophores and xanthophores appear on the yolk surface as well as on the embryonal body. The hatched larva is elongate in shape with 55-64 myotomes, and the anus is situated at the posterior part of the body. Anguillida. Muraenesox cinereus (Fors k al), Ophicthidae No. 1-6, Anguillida No. 1-9 and a single species probably belonging to this order are known from Japanese waters. The egg is globular, large, measuring 1.60-4.80 mm in diameter, with wide perivitelline space. The yolk is segmented. The oil globule is present or absent. The egg membrane is smooth, without any conspicuous structure and glistening. The hatched larva is elongate and compressed, with more than 100 myotomes. Some species is provided with 3-5 larval teeth on each side of both the upper and lower jaws. The eggs of apodal fish can be divided into two groups according to the presence or absence of the large melanophores situated along the ventral median line of the hatched larva. The larvae with large melano-phores seem to belong to the family Ophichthidae. Belonida. Oxyporhamphus micropterus micropterus (Cuvier et Valenciennes) and Exocoetidae No. 1 are known from southern waters of Japan. The egg is globular and considerably large, measuring 1.82-2.1 mm in diameter. The perivitelline space is narrow. The yolk is not segmented, lacking oil globule; 40-80 rudimentary tendrils are seen on the whole surface of the egg membrane. Syngnathida. Fistularia villosa Klunzinger and F. petimba Lac`pede a r e known from the Java Sea and southern waters of Japan. The egg is somewhat large, measuring 1.50-2.09 mm in diameter. The perivitelline space is narrow. The egg membrane is smooth without any conspicuous structure, but F. villosa has double egg membrane. The yolk is not segmented without oil globule. During the course of the egg development melanophores and xanthophores appear on the yolk surface and on the embryonal body. The hatched larva is moderately elongate with 82-86 myotomes, and the anus is situated at the posterior part of the body. As h as already been pointed out, the proportional size of various parts of the body and pigmentation of the hatched larvae change rapidly during the course of larval development. Therefore in the present paper, the larvae observe d just after hatching are called " larva just hatched," and those of which the author could not determine the exact hatching period but seem to be in the stage within several hours after hatching are called " larva newly hatched."