Wirenia argentea ontogeny - schematic representation of the development of test and epidermis. Lateral view, ventral side to the left; test cells grey, other ectdodermal cell layers black, mesodermal tissue dotted (inner organs not depicted). A. Day 1 larva. B. Day 3 larva with trunk rudiment. C. Day 4 larva with short trunk. D. Day 7 larva, note dense ventral ciliation (foot) and ingression of non-test ectodermal tissue (epidermis) below posttrochal cells. E. Day 10 larva with one of the ventral posttrochal cells shed and remaining posttrochal cells sitting on top of epidermal material; note inversion of telotroch and dorsal sclerites. F. Day 14 postlarva, posttrochal cells shed, pretrochal cells covered by epidermis and largely absorbed.