Distortion coordinates (Cartesian transformations) are used to compare the ontogenetic allometry in cranial morphology of first, second, and third instars of Hydaticus bimarginatus (Say). The most significant difference in the dorsoventral view is the expansion of the posterior lateral margins. Cranial expansion is likely due to an increase in the mass of the adductor muscles which are responsible for closing the mandibles. The ontogenetic shift in head orientation to a more subprognathic position evident in the analysis of lateral silhouettes indicates that second and third instars may be adapted to feeding on substrate associated prey. These differences are thought to reflect possible changes in prey regimes and habitat preference occurring during larval development.
Bridges, Ross S.; Wall, William P.; and Barman, E. H.
"An Allometric Analysis of Ontogenetic Changes (Variation) in the Cranial Morphology of Larvae of Hydaticus bimarginatus (Say) (Coleoptera: Dytiscidae: Dytiscinae),"
Georgia Journal of Science, Vol. 67, No. 2, Article 9.
Available at: https://digitalcommons.gaacademy.org/gjs/vol67/iss2/9