While insect and crustacean welfare has gained scientific attention, the welfare of other invertebrates — mollusks, worms, echinoderms — remains understudied. Expanding our circle of moral concern requires understanding what we know and do not know.
Invertebrate welfare science is at an early but important stage. For most invertebrate groups, we lack the behavioral, neurological, and evolutionary evidence needed to assess sentience confidently. This uncertainty should prompt caution rather than dismissal — the precautionary principle suggests that when suffering is plausible and stakes are high (given invertebrate populations in the billions), erring toward reducing unnecessary harm is reasonable. Even where sentience is uncertain, practices that cause mass invertebrate mortality without consideration deserve scrutiny. As invertebrate neuroscience advances, our moral frameworks should expand to incorporate new evidence rather than resisting it.