Postembryonic development of dorsoventral and longitudinal musculature in Pycnophyes kielensis (Kinorhyncha, Homalorhagida).

We investigated the development of dorsoventral and longitudinal musculature in all postembryonic stages of the kinorhynch Pycnophyes kielensis. Although the earliest stages have only 8 externally separated trunk segments, they already possess dorsoventral muscles for 10 (prospective) trunk segments. The last, 11th, pair is added in the third juvenile stage.