Do rotifer jaws grow after hatching?

The hard articulated jaws of some pseudocoelomte metazoans were recently used in reconstructing their phylogenetic relationships, but we still do not know if these structures could change in size and shape during the life of individuals, and experimental data are lacking on their post-embryonic development. Rotifers are one of the groups in which hard articulated jaws, called trophi, are well known, and are widely used taxonomically. Here we report on SEM study of trophi of rotifers of different ages, to determine if the trophi structures change in shape and/or in size during post-embryonic development. We used linear measurements and geometric morphometrics analyses from scanning electron microscopic pictures of trophi of Cupelopagis vorax, Dicranophorus forcipatus, Macrotrachela quadricornifera, Notommata glyphura, Rotaria macrura, R. neptunoida, and R. tardigrada. Results for these species show that trophi do not change after hatching, either in size or in shape. In contrast, data on Asplanchna priodonta reveal trophi growth after hatching.