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Novel Morphological Traits in the Early Developmental Stages of Temnopleurus toreumaticus

¹ Biological Institute, Faculty of Education, Yamaguchi University, Yamaguchi 753-8513, Japan
² Laboratory of Environmental Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8512, Japan

^* To whom correspondence should be addressed. E-mail: chisak{at}yamaguchi-u.ac.jp

We have re-observed in detail the development of the sea urchin species Temnopleurus toreumaticus, which is considered to be a typical indirect-developing species with a feeding larval stage. In this re-observation, we discovered two new morphological traits in the early embryonic stages of T. toreumaticus. The first trait is that, immediately after fertilization, the egg enters a stage in which wrinkles form on its surface as a result of actin polymerization. The second new trait is that the blastulae form wrinkles; in sea urchins, this has previously been known only in direct-developing species that have a nonfeeding larval stage and form wrinkles during the blastula stage, before hatching. These phenomena indicate that after fertilization, the egg of T. toreumaticus undergoes a surface transformation that is unprecedented in echinoderms, and that an indirect-developing sea urchin can form a wrinkled blastula.