Conserved topological patterns and heterochronies in loliginid cephalopods: comparative developmental morphology of the oval squid Sepioteuthis lessoniana

Summary

Development of the oval squid Sepioteuthis lessoniana is marked by a large embryonic size resulting in the most fully developed planktonic hatchlings within loliginids. We analyzed the embryonic development with special reference to the external morphology and the surface ultrastructure with a scanning electron microscope to identify both phylogenetic conservation and diversity of structures in the organogenesis of a loliginid. Developmental states of various cilia, namely the scattered, tuft, and uniform types are described. The ciliature pattern of S. lessoniana is more closely similar to the patterns of other loliginids than to those of sepioids and sepiolids, although characteristic numerous uniform-type cilia exist in the embryos of S. lessoniana. The conserved pattern can be recognized in the organogenesis of S. lessoniana and other loliginids; on the other hand, heterochronic variations are noted, particularly in photosensitive organs and chromatophores. Eye pigmentation does not start at the same stage as in other loliginids and it is unlikely that the heterochronic variation of eye pigmentation is correlated to embryonic size. Chromatophores of S. lessoniana appeared earlier than those of other loliginids. Although hatchlings of S. lessoniana have a more strongly developed arm crown than other loliginids, the suckers arise at similar stages. These ontogenetic variations in loliginids may be considered together with the early mode of life.

Key words:

• Embryonic development
• cephalopods
• ciliary pattern
• SEM
• phylotype