In triploid tardigrades, oocytes are formed by mitotic divisions, yielding triploid eggs. Fertilization is external, hut protected. As a female is molting, males may introduce spermatozoa into the gonopore or cloaca. The spermatozoa travel up the oviduct into the ovary where fertilization occurs. Cleavage is total and apparently equal.
Gastrulation occurs by unipolar proliferation.
Five pairs of coelomic pouches form. The posterior pair fuse to form the gonad. The others degenerate and form the buccal apparatus and body muscles. The embryo undergoes direct development. After hatching, growth occurs by increase in cell size, not number.