As a species evolves from being a coastal or shallow water species to being an oceanic species, it needs to adapt to the challenges posed by the different environment. Darkness, for one thing – below 200m there is effectively no sunlight. Many organisms have adapted to the darkness by using bioluminescence for communication, signaling, defense etc. H. dispar has photophores filled with a symbiotic bacteria that produce bioluminescence. Instead of releasing an ink-cloud when disturbed, H. dispar releases a luminescent cloud to confuse would-be predators.
As another adaptation to the dark, the bodies of hatchlings are very nearly transparent leading researchers to conclude that the eggs may be released into the water column rather that at the sea floor. However, the only H. dispar egg that has been collected was caught in a bottom trawl, suggesting that they might attach eggs to the bottom like other sepiolids! This underlines how little we know about this (and most) oceanic species and how much more study is needed!