Novel morphological traits in the early developmental stages of Temnopleurus toreumaticus.

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.