Meeting Abstract

102.2  Sunday, Jan. 6  Scaling of the Hydrostatic Skeleton in the Earthworm, Lumbricus terrestris KURTH, J.A.*; KIER, W.M.; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill jkurth@live.unc.edu

The structural and functional consequences of changes in size or scale have been well studied in animals with rigid skeletons, but relatively little is known about scale effects in animals with hydrostatic skeletons. We used microscopy and histology to examine the scaling of mechanically important morphological features using an ontogenetic size range of the earthworm Lumbricus terrestris from 0.03g-12.89g. Each worm was anesthetized and laid out under a dissecting microscope, and measurements were taken of its elongated body length as well as diameter. The worms were then sacrificed and several segments were removed and embedded in glycol methacrylate plastic. Our results indicate that several functionally important morphological features do not maintain geometric similarity with ontogeny. We found that the cross-sectional area of the longitudinal muscles (which are used to radially expand the worm) scaled as body mass to the ~0.6 power across segments, which is significantly lower than the 0.66 power predicted by isometry. However, the cross-sectional area of the circular muscles (used to axially elongate the worm) scaled as body mass to the ~0.8 power across segments, which is significantly higher what is predicted by isometry. These data suggest that as worms increase in body size, they may produce relatively greater forces during axial elongation but relatively weaker forces during radial expansion than what is expected by scaling with geometric similarity.