Urata Makoto, Iwasaki Sadaharu, Ohtsuka Susumu, Yamaguchi Masaaki
Takehara Marine Science Station, Setouchi Field Science Center, Graduate School of Biosphere Science, Hiroshima University, Takehara, Hiroshima, 725-0024, Japan.
Evol Dev. 2014 May;16(3):149-54. doi: 10.1111/ede.12075. Epub 2014 Apr 8.
Spawnings of Glandiceps hacksi (Hemichordata: Enteropneusta) were stimulated in the laboratory by a brief increase in temperature, and the development from fertilization through metamorphosis is described for the first time for a member of the family Spengelidae. When fertilized, the spawned female gametes, which are primary oocytes, rapidly raise a fertilization membrane and undergo two maturation divisions. Holoblastic, radial cleavage produces a blastula; a gastrula then forms by invagination from the vegetal pole, and the blastopore closes soon thereafter. In previously described enteropneust embryos, the archenteron buds off the protocoel before the latter connects to the exterior via the proboscis pore. By contrast, in G. hacksi the archenteron precociously connects with the exterior before the protocoel forms. Soon thereafter, the embryo becomes uniformly ciliated and then hatches from the fertilization envelope at approximately 32 h (15°C culture temperature). At day 3 of development, the protocoel separates from the gut, which establishes a mouth opening to the exterior; by this time, the gut has differentiated into an esophagus, a stomach, and an intestine that opens posteriorly as an anus. The larva grows to form a tornaria with distinctive pigment patches along its ciliary bands.
在实验室中，通过短暂升温刺激了哈氏鳃裂虫（半索动物门：肠鳃纲）的产卵，并且首次描述了斯彭氏鳃裂虫科成员从受精到变态的发育过程。受精时，产出的雌配子即初级卵母细胞会迅速升起受精膜并经历两次成熟分裂。全裂、辐射状卵裂产生囊胚；然后原肠胚通过植物极内陷形成，随后胚孔很快闭合。在先前描述的肠鳃纲胚胎中，原肠在与外部通过吻孔相连之前就从原腔分出。相比之下，在哈氏鳃裂虫中，原肠在原腔形成之前就早熟地与外部相连。此后不久，胚胎全身长满纤毛，然后在大约32小时（培养温度15°C）时从受精膜中孵化出来。在发育的第3天，原腔与肠道分离，肠道形成通向外部的口；此时，肠道已分化为食管、胃和向后开口作为肛门的肠。幼虫生长形成具独特色素斑带的柱头幼虫。
