Does the number of sclerotised structures used for the systematics of monogeneans change with age? A study of the monocotylid Dendromonocotyle pipinna.

Although monogenean systematics is often based on the morphological analysis of sclerotised structures, their variation with size or age is rarely investigated. Two hundred specimens of the monocotylid Dendromonocotyle pipinna Chisholm and Whittington 2004 were studied. In the haptor, the numbers of marginal papillae, of sclerites in the marginal papillae and of sclerites in the septa did not change according to the size; however, the mean interval between the sclerites in the septa increased linearly with body length. This suggests that, at least in certain cases, valuable systematic descriptions can be made on incompletely grown monogeneans.