SEP�LVEDA, R.D.; Universidad Austral de Chile: Analyzing allometry in an intertidal gastropod using geometric morphometrics

Traditional morphometrics have assumed that gastropod shells grow at isometric fashion. Geometric morphometrics is specifically aimed to characterize changes in shape independent of size. The aim of this study was to determine the variation in shape in the intertidal snail (A. monodon), using partial warps. Photographic records of the ventral face of 195 shells of Acanthina monodon were taken and ten landmarks were defined to measure shape deformations with respect to a consensus configuration (CC). The tpsSmall software was used to consider the centroid size and the consensus configuration by means of Procrustes superimposition. Additionally, was used to consider the relationship between distance in the Kendall�s space and its projection on the tangent space. The tpsRegr software was used to measure the relationship between the centroid size and partial warps. The results showed that the growth of the snail was allometric. The non-affine general folding in the bending energy was produced by the landmarks related to the thickness lip, and the siphonal channel in the first four principal warps. In the three remaining principal warps, the landmarks were related to the thickness lip, apex height and the siphonal channel. Related to the consensus configuration Acanthina monodon present local deformations in the thickness lip and siphonal channel in small individuals (to the left CC). In large snails (to the right CC), global deformations appear due to the apex height, the siphonal channel and thickness lip variations.