While crustaceans have received growing welfare attention, other aquatic invertebrates including worms, molluscs, and echinoderms remain almost entirely outside welfare consideration.
The boundaries of moral consideration have expanded repeatedly throughout history, and the question of which invertebrates deserve welfare protection is an active frontier. The precautionary principle suggests that in the face of genuine uncertainty, minimizing potential suffering is appropriate. This does not require treating all animals as equivalent, but it does suggest caution about activities that might cause suffering to organisms whose sentience we cannot rule out. Research investment in this area is urgently needed.