Putting in shape: towards a unified approach for the taxonomic description of monogenean haptoral hard parts.

Among monogeneans, haptoral hard parts provide prominent morphological characters upon which identifications are largely based. Traditionally, morphometric approaches are based on the use of arbitrary collections of linear distance measurements between landmarks. An exhaustive review of the specific diagnoses published in the journal Systematic Parasitology highlights the fact that an intricately important number of measurements are used to describe the same morphological features. Hence, this does not allow relevant comparison between studies and may have caused confusion in the literature. More importantly, a significant proportion of diagnoses commonly used do not maximize the amount of information available from morphological features, and sets of linear measurements between landmarks do not properly allow the complete reconstruction of the shape of haptoral hard parts. Given this prominent bias and the disparate use of traditional methodologies, I suggest the use of alternative methods in systematic parasitology that fully take into consideration the shape of morphological features. In addition to these considerations, a move toward placing shape at the centre of automated species recognition would be mutually beneficial for both taxonomists and non-taxonomists.