スルメイカOmmastrephes sloani pacificus STEENSTRUPの繁殖生態に関する研究 : III.初期発生と孵化直後の幼生の形態

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In the early summer of 1958 and 1959, a number of the squid, Ommastrephessloani pacificus Steenstrup, were made to spawn under expetimental conditions on the Shore off Urago Bay, Oki Islands (Hamabe, Reports I-II), Subsequently, some 13,000 eggs obtained from six females were reared in various manners to observe the early embryonic development. Decription of the present paper is based on the observation of 170 larvae hatched out in glass aquaria during two experiments performed for about four or five days in May and June 1959. Water temperature in the aquaria ranged from 14 to 22℃, and chlorinity from 19.07 to 19.33‰ (Table 1). The fertilized egg of the squid is demersal, telolecithal, and ellipsoid in shape being 0.8mm. in major diameter and 0.7mm. in minor diameter. During embryonic development, it becomes nearly spherical, attaining 1.0-1.3mm. in diameter Just before hatching. The cleavage pattern is the partial type (discoidal cleavage). Twelve hours after spawning, the blastoderm exceeds the equatorial plate.In 24 hours, the germ layer grows almost all over the egg, with the origins of the shell and mantle developing on the animal pole. Forty hours after, the origin of the head including eyes and mouth, develops, riding on cell masses, across the ectodermal edge into the vegetal pole, and thus it seems to cover the whole yolk cell. The embryo turns into a lemon-like shape 50 hours later when the mantle is apparently contiguous to the cephalic part. The other organs of the body develop in 70-80 hours. The larva hatches out in 102-113 hours. At the time of development, around 40-60 hours, a number of granular particles are discharged from the embryo into the perivitelline space. The granular discharge is followed byautonomic rotation of the embryo. As the number of ganules decreases and the rotation slows down, the embryo adheres to the egg membrane. Two different types of the hatching process were observed depending on whether or not the egg membrane was swollen ehough. In an well swollen egg, the embryo floating in the perivitelline fluid adheres to the membrane with the Hoyle's organ, then begins jostling inside. The egg membrane is softened by enzyme secreted from the Hoyle's organ(Fumoto and Hirose '57), until the embryo breaks it and instantly hashes out with the perivitelline fluid (Figs.4, 70-72). In another egg relatively small in size, the Hoyle's organ seems to play the same function as in the large egg. However, the egg membrane is rather physically expanded and broken mainly by the embryonic palsation. The observation of the hatching process has suggested that thepresent species in nature would normally follow the former type of the process.Immediately after hatching the larvae measured, in mantle length, respectively, 0.74mm. (Fig.4, 72), 0.90mm. (Fig.4, 66) , 0.94mm. (Fig.4, 68), 0.99 or 1.02mm. (Fig.4, 64 and 65). Morphological features of the larval squid are: The absence of the third and the fourth arms, The presence of the vestigial yolk-sac under the armcrown which proves that the embryo forms an involution type at the gastrular stage, presence of the tentacle which is fairly large but has not so developed as to form the rostrum (Russel).
社団法人日本動物学会の論文
1961-12-15

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日本海区水産研究所浦郷支所

スルメイカOmmastrephes sloani pacificus STEENSTRUPの繁殖生態に関する研究 : III.初期発生と孵化直後の幼生の形態

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