Research on evolution of larval skeleton in sea urchin: Echinometridae

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To understand the morphological variety of larval skeletons within the Echinometridae, a detailed comparative study was performed, which included quantitative morphometry. In order to extract skeletal characters which are stable in four-armed pluteus stage, we compare skeletal characters of two-day-old larvae (prior to feeding) with those of larvae fed for a few days. By this way, we found five skeletal characters of body-skeleton are stable four-armed pluteus. Morphological variations among the Echinometridae species were summarized as the difference in the number of spine and posteroventral transverse rod, and those in the shape of body-skeleton, and we found that based on these characters species can be identified from larval skeleton. Significant correlation can be detected between skeletal characters, such as between lower body length and number of spines, and between upper body length and posteroventral transverse rod length. We have also performed molecular phylogenetic analyses for 15 species of Echinometridae, together with some experiments on functional aspects of larval morphology.