Many other invertebrate animals have elements of a
pain system (Sherwin 2001). However, references are
quoted here for Cephalopoda and Decapoda only.
Insects and spiders have not been clearly demonstrated to respond to pain in a way that suggests that
they are aware of it. Decapod crustaceans show behavioural, anatomical and physiological indications of having a sophisticated pain system. They have nociceptors that supply information to ganglia involved in
learning (Sandemann et al. 1992). Avoidance learning
to noxious stimuli occurs in crayfish (Kawai et al. 2004)
and sand lobsters (Sherwin 2001). Analgesic opioids
affecting responses and learning have been reported
in shrimps and crabs etc. by Maldonado & Mirata
(1982), Lozda et al. (1988) and Bergamo et al. (1992).
As in vertebrates, naloxone inhibits the opioid action
(Dyakonova 2001).