The embryonic development of the Hawaiian bobtail squid (Euprymna scolopes).

A staging series based on easily distinguishable morphological features is a basic and necessary tool for developmental studies. It provides a consistent reference for comparisons between independent studies, negates the need to know when fertilization occurred, allows correlation of the phase of development with the time of development (to facilitate collection of embryos at specific stages), and allows comparisons between species. Given the growing interest in Hawaiian bobtail squid (Euprymna scolopes) as a contemporary cephalopod developmental system, this article provides a detailed survey of E. scolopes embryogenesis from cleavage through hatching under controlled environmental conditions, including detailed descriptions of externally visible morphological features that are easily distinguished in either live or freshly fixed embryos under a dissecting microscope. Photomicrographs are also provided to aid in the accurate and rapid staging of E. scolopes embryos.