THE EARLY DEVELOPMENT OF LAMPETRA MORII

Lamprey is of considerable model organism to subject of vertebrate evolution and developmental biology. The current study investigated the morphological characteristics and the growth pattern of embryos, yolk-sac larva and ammocoate of Lampetra morii. The results indicated that the cleavage of lamprey zygote was holoblastic cleavage and the embryology had been subdivided into cleavage, blastula, gastrula, neural plate and groove, head protrusion, prehatching and hatching. The newly-hatched larva breaks through the fertilization membrane at 11—12 day-post-fertilization at water temperature of (18±1)℃. The newly-hatched larva had body weight with (0.00032±0.00002) g and total length with (0.29±0.02) cm. During yolk-sac stage, the body weight and total length of larva generally increased over time. The snout length, eye length, postocular length, disc length, prebranchial length, branchial length, head length, trunk length, tail length and cloacal slit length exhibited allometric growth. The ammocoete stage reached when yolk extruded from the anus and the digestive tract completed at 15 day-post-hatch. In 5 months after hatching, the body weight and total length of ammocoete generally increased over time. The melanophores were extensively distributed and increased in ammocoete. The 5-momth old ammocoete had body weight of (0.07±0.01) g and total length of (3.87±0.32) cm. The early development of L. morii is the basic data for artificial culture and developmental biology, which is the basis for the model organism.