Abstract
Crustaceans exhibit a great diversity of morphological characteristics that are useful for inferring the general habits of species. In cheiragonid brachyuran crabs such as the horsehair crab Erimacrus isenbeckii, which live in the cold water, less attention has been paid to differences in external morphology between sexes. Our group recently identified several morphological characteristics on the carapace of the horsehair crab to distinguish females from males by geometric and measurement-based morphometric approaches. In this study, we constructed 3D images of the carapace that were then applied in the establishment of new validation indices to identify adult females and males. At first, the density patterns of tubercles with setae on the carapace were different between sexes. Even in sexually-matured individuals, smaller females had more dense tubercles on the carapace than males. Second, the curvature radius of the cross-section of the carapace also showed clear differences between sexes. The carapace of females was rounder than that of males. This study provides new tools to distinguish females from males using 3D imaging, and is the first evidence to quantitatively show sexual differences in “roundness” of the carapace in the horsehair crab. 3D-based morphometrics using curvature radius will be a useful index that can be applied for geographic comparisons and for other brachyuran species.a
