Entities › Animals and other organisms › Invertebrates with brains
Shore crab / crayfish
Carcinus maenas; Procambarus / Astacus spp.
Crabs and crayfish. A 2021 government review found strong evidence that true crabs are sentient.
- Neurons
- No published count
Evidence
- Shore crabs learn to avoid a shelter that gives shocks. They also trade off avoiding shocks against how good the shelter is. That fits the pain criteria.Magee B, Elwood RW (2013) Shock avoidance by discrimination learning in the shore crab (Carcinus maenas) is consistent with a key criterion for pain. J Exp Biol 216(3):353-358. doi:10.1242/jeb.072041.
The 2021 sentience review
Confidence that each of the eight sentience criteria is met, for true crabs (brachyura):
- high The animal possesses receptors sensitive to noxious stimuli (nociceptors)
- very high The animal possesses integrative brain regions capable of integrating information from different sensory sources
- low The animal possesses neural pathways connecting the nociceptors to the integrative brain regions
- very high The animal's behavioural response to a noxious stimulus is modulated by chemical compounds affecting the nervous system (e.g. local anaesthetics, analgesics, opioid-type systems)
- low The animal shows motivational trade-offs, in which the disvalue of a noxious or threatening stimulus is weighed against the value of an opportunity for reward, leading to flexible decision-making
- very high The animal shows flexible self-protective behaviour (e.g. wound-tending, guarding, grooming, rubbing) of a type likely to involve representing the bodily location of an injury or noxious stimulus
- high The animal shows associative learning in which noxious stimuli become associated with neutral stimuli, and/or novel ways of avoiding noxious stimuli are learned through reinforcement (habituation and sensitisation do not count)
- very low The animal shows that it values a putative analgesic or anaesthetic when injured (e.g. self-administers it, or learns to prefer a location where it is available)
The New York Declaration on Animal Consciousness (2024) finds at least a realistic possibility of conscious experience in all vertebrates and in many invertebrates, including cephalopods, decapod crustaceans and insects.