Observations on the morphology of embryonic and larval development in Styela canopus Savigny

The morphological characters on different developmental phases of embryo and larva and the schedule of the whole early developmental process in Styela canopus were observed and described.The types of reproduction and early development as well as the morphology of egg and larva in different ascidian species were compared.Styela canopus is oviparous.Its egg,230.4~336.0 μm in diameter,is equipped with extraembryonic cell layers measured 43.2~63.0 μm thick.The early development of Styela canopus is typical urodele development,including fertilization,cleavage,gastrulation,tadpole in membrane,tadpole,initiating metamorphosis and juvenile.The tadpole of Styela canopus,with a length of 0.6~0.9 mm,consists of trunk and tail.There are obvious notochord,ocellus and adhesive papillae in the tadpole.Under the water temperature of(25±0.5)℃ and the salinity of 27.0,the larva was hatched after 9.5~11.0 h since the fertilization.