Embryonic development of southern calamary (Sepioteuthis australis) within the constraints of an aggregated egg mass

A post-cleavage embryological scheme was established for southern calamary Sepioteuthis australis. Using this developmental scheme, intra- and interspecific comparisons were made. Sepioteuthis australis development most closely resembled that of its tropical congeneric species, S. lessoniana, with only a few subtle heterochronies. The greatest developmental difference was observed when comparisons were made with Loligo pealei. These differences were attributed to developmental duration and respective egg sizes. Within S. australis, variation in developmental rates among embryos was associated with the size of the egg mass, with less variation evident in smaller egg masses. Embryos located on the periphery of the egg mass and at the distal or unattached end of an individual egg strand developed significantly faster than those located deep within the egg mass. On average, embryos in small egg masses, consisting of five individual egg strands, developed significantly faster than those in dense aggregations (>100 strands).