Author’s Note: This article was originally published in The Vegan magazine, Winter 1992. The Law relating to Cephalopods has been changed since then and I give an update at the end of this article. Thanks to the Vegan Society (https://www.vegansociety.com/) for publishing this and for letting me re-use it.
Invertebrates range in size from the microscopic to the giant squid. They comprise 95% of all animal species. The huge number of individuals in these species makes vertebrate species seem almost insignificant. Invertebrates are extremely successful colonizers of this planet and many are essential to the stability of the ecosystem. Invertebrates are often interesting, attractive, or rare. Fourteen British invertebrate species are so near extinction that it is illegal to kill, take, or sell them.
Currently, the Animals (Scientific Procedures) Act 1986 covers only vertebrates. However, the Home Office is considering extending the list of animals requiring a licence for use in laboratory experiments to include squid, octopus, cuttlefish and other cephalopods. 
The Protection of Animals Act 1911 (1912 Scotland) protects all species of animals from suffering caused by the commission or omission of any act – but only where the animal is captive! Therefore, captive invertebrates are protected by the Act if they can be shown to be capable of experiencing pain.
Cephalochordata (an invertebrate subphylum related to vertebrates, not to be confused with cephalopods) were included under the 1876 Cruelty to Animals Act.
Learning in invertebrates
Leeches and earthworms have a central nervous system (as with humans, not all responses to stimuli are automatic), a memory and advanced learning abilities (in response to repeated aversive stimuli they adapt).
“Like the cephalopod molluscs, the social insects and decapod crustacea (e.g. lobsters and crabs) also display considerable learning abilities. For example, ants and rats show comparable speeds when learning complex mazes and the sentience of decapod crustaceans is acknowledged by their inclusion in Norway’s animal experimentation legislation.” 
In Volume 3 of Invertebrate Learning: “There is no justification for regarding the bees’ ability as inferior to most vertebrates … their learning ability is on the same scale as that of rats. 
“The capacity of the (invertebrate) nervous system for spontaneous activity – its role in initiating events – is as crucial as its ability to respond to changes in the environment.” 
Many invertebrates show aversive reactions to noxious stimuli.
Insects commonly display ‘associative learning’ but some species of ant also use tools, implying the use of ‘insight learning’. Planaria (a type of flatworm) show cognitive memory of their environment.
Paramecia seem to exhibit complex learning ability, and even the ‘simple’ protozoan called amoeba will withdraw from a region that contains noxious chemicals and show an avoidance reaction upon contacting other objects. “Habituation and elementary associative learning do occur in some of the protozoans.” 
All vertebrates possess, as far as we know, pain receiving or nociceptive cells (alternative names are N-cells or Noxious Stimuli Receptors). “Pain is a specific sensation entity … there exist specific sets of neural elements that are responsible for these sensations (Burgess and Perl). These elements are classified as ‘pain’ cells or nociceptors”. 
As a first definition we can say that pain is so important that, “Any animal with a central nervous system can feel pain.” We can go further and hypothesize that, “Any life form that has the ability to recognize noxious stimuli, that can learn, and can remove the area at risk from the noxious stimuli can feel pain.”
In The Neurobiology of Pain, B Lynn (of Dept. Physiology, University College London) accepts the experiments of Torebjork and Ochoa which show that “microstimulation of nociceptive afferents is always painful.” Lynn goes on to say, “From behavioural observations many invertebrates show aversive reactions to noxious stimuli so there are probably many types of invertebrate nocicepter awaiting study.”
The leech has four nociceptive cells in each segmental ganglion. W. Paton in Man and Mouse has pointed out that the leech and snail contain certain receptors for pain killing drugs. Investigations also indicate the presence of opioids (pain killers) in insects. The earthworm produces opiate like chemicals and the presence of opiate receptors is suggested. Earthworms have substance P and ACTH (the stress hormone) present in neurons of the cerebral ganglion and the subesophageal ganglion. Allied to the presence of 5HT and endogenous opioids, this suggests a stress adaptation system. “Earthworms do have opiates, so they must have pain to block!” 
It is also possible that pain can be transmitted without the presence of N-cells. “Given that pain is biologically so important, we would expect an animal that had any consciousness at all to be conscious of painful stimuli.” 
Indeed, I would argue that pain cells evolved before any other type of sensory cell. This would accord with N-cells’ physiology and with the evolutionary importance of pain. Perhaps all sensory cells developed from N cells. Pain is the most important sensation for the majority of animals.
The RSPCA Today magazine, Summer 1988, (article by Bryony Cobby) states that earthworms have nociceptors and protozoa produce opioids.
Price, Assistant Vet at Glasgow Vet. Dept. told the’ author, “It is obvious that certain invertebrates feel pain.”
“But I am sure that insects can feel pain if the right stimulus is given … I have no doubt that Rhodnius feels pain.” 
“I make it clear in my writings and lectures that we should assume that they [invertebrates]do [feel pain]and take appropriate steps to minimize this.” 
“Experimental work on them [invertebrates]is frequently performed without adequate regard for their welfare.” 
Research Defence Society spokesman, DH Smyth, wrote, “On the whole, many invertebrates look as if they felt less pain than mammals.” (Thereby accepting that invertebrates feel some pain!)
Invertebrates are used widely in educational establishments. “Invertebrates [such as protozoa and earthworms]should be treated as humanely as other animals.”  Another school text recommends that all invertebrates that undergo experiments thought to involve pain (i.e. removal of tissues from mussels, chironomus larvae and aquatic invertebrates) must be under anaesthesia and the invertebrate “humanely” killed before recovery. (And yet poisoning, boiling alive and drowning are all cited as methods of approved painless killing for protozoa, crayfish and snails respectively.)
“Insects do, however, seem to feel distress when prevented from carrying out their normal activities. An incarcerated bee tends to panic as a result of hormonal and other chemical discharges into the blood and soon dies through nervous stress,” writes Anthony Wooton in Insects of the World. “Neurophysiological stress and restlessness caused by overcrowding and jostling” are discussed in relation to the locust. Wooton also describes the female earwig as, “exceedingly selfless in her devotion to her nymphs”.
Compassion towards invertebrates is called for by KP Stoller in Animals Voice magazine, vol. I, number 2.
“All kinds of cells and organisms, from bacteria to people, respond to harmful environmental conditions by synthesizing stress proteins.”  (This does not necessarily mean opioids.)
“Anaesthetics have been developed and should be used at least for all multicellular forms of macroscopic dimensions.” 
“Crabs have well developed nervous systems and naturally, can be expected to feel pain.” 
More recently, the UK Government’s Animal Procedures Committee commented: “There is evidence that higher invertebrates, most notably cephalopods, have no less a capacity to suffer than many vertebrates.” 
The experiments of M.J. Wells at Cambridge University are detailed in his book, Octopus. These experiments include electric shock, oxygen starvation until death (taking 20 minutes), blinding, and destruction or removal of part of the brain. In his own words, octopuses exhibited “distress,” “will run away with every appearance of fear if you are beastly to them;” were “scared,” “withdrawn” and “startled;” experienced “stress;” and were “gentle.” Wells also describes how “pain” signals result from “punishment” experiments. He also writes how he is, “astonished that the world is somehow prepared to pay me to play with living things for a living.”
The octopus photographed in J. Zool. Lond. 201,185-204 (1983) is shown vainly trying to protect its wound from the experimenters, and it was said by them to, “represent a reaction very similar to that seen in man under equivalent stimuli.”
Octopuses, cuttlefishes, and at least some squids are well equipped for learning. They solve problems of training and retraining as successfully as rats. They have good memories, including short term, intermediate, and long term. “Extraordinarily intelligent, the octopus performs as well as mammals in discrimination experiments.” 
“The signals associated with positive (good taste) and negative (pain) training” are discussed, in relation to the octopus, in A Life of Invertebrates by WD. Russell-Hunter. “Cephalopods are so ‘intelligent’ that they appear to express something like mental conflict when frustrated.” 
“If a diver is too rough with an octopus, even without actually hurting it physically, it happens that the animal goes into a state of emotional shock and sometimes dies,” writes Joanne Duffy (holder of a Masters Degree in Marine Biology) in Octopus and Squid, the Soft Intelligence, by Cousteau and Diole.
Myron Stearns, speaking of a man who had been prodding an octopus, writes: “Just as he lifted the creature above the rim of the aquarium it shot its brown ink all over his shirt. It didn’t squirt at anyone else, although we were just as close; it squirted at the man who had been tormenting it. And not until it had a clear shot.” 
“In 1488, slugs were warned against consuming crops, else they suffer excommunication … In 1541, the Church [The Church of Christ] condemned a plague of locusts… In 1587, weevils were tried.” 
“Kill not the Moth nor Butterfly, for the Last Judgement draweth nigh,” wrote William Blake, a Christian.
In Love All Creatures, the Islamic Foundation states that “Allah forbids that any man should hurt them [ants or other animals].”
Buddhists and Jains have a long history of respect towards invertebrates. Many monks and nuns, of both disciplines, will not dig the earth for fear of harming earthworms, etc. Jains will feed ants and other invertebrates. Even fleas and lice were protected by law in the ancient Jain kingdoms of India.
The Oie gelbe Kirche, a Buddhist text (translated by R. Bleichsteiner), records how “During a debate with the Saskya Pandita which the Venerable Tsong-kha-pa had about AD 1400, his opponent, probably absentmindedly, crushed a louse between his nails. Tsong-kha-pa interrupted him, exclaiming, ‘While we are here debating these abstruse metaphysical subtleties, I hear the laments of a fellow creature rising to the sky!'”
When I organized the Buddhist Animal Rights Group, we contacted many animal rights and welfare groups on the subject of invertebrate pain, outlining the need for further investigation and public education. Unfortunately, no group was willing, or able to assist.
The available evidence suggests strongly that many invertebrates are capable of experiencing pain and suffering. There is no logical reason why a (live) lobster-boiling restaurant or squid experimenter should not receive the same attention as abusers of vertebrate animals. If a prosecution cannot be brought under the Protection of Animals Act, then the animal rights movement should consider highlighting particular areas of concern – for example, experiments on octopuses. It is clear that there exists an urgent need for further (non-violent) research.
References Guardian 21st October, 1992  Philip Churchwood, Black Beast.  Corning, Ryal and Willows, 1972  The Invertebrates: A New Synthesis by RSK Barnes, P Calow and PJW Olive.  Encyclopaedia Britannica.  From Methods of Animal Experimentation by Gay, article by Lineberry.  New Scientist, 28th July, 1979  Man and Mouse by W Paton.  Do Insects Feel Pain?‘ by VB. Wigglesworth, Dept. Zoology, Cambridge University; article in Antenna 4, (1980).  JE Cooper of the Royal College of Surgeons, England in a letter to the Buddhist Animal Rights Group  Vet. Record, 118 (1986). JE Cooper, PMahaffey and K Applebee.  Technicians Guide, Scotland  New Scientist. 1 April, 1989. Article by R Anderson.  The Use of Animals in Research, Development and Testing, Parliamentary Office of Science and Technology (1992).  New Scientist. 10th December, 1988.  Fed. Proc. 28, 1557. ‘Invertebrate Anaesthesia’  Universities Federation for Animal Welfare publication.  BBC Wildlife. Nov. 1983.  Marvels and Mysteries of our Animal World.  From, The Criminal Prosecution and Capital Punishment of Animals by EP. Evans.
2016 UPDATE TO THE ABOVE
The Law relating to Invertebrates changes from Country to Country. Billions of Invertebrates are killed each year for food. There seems to be no regulations in place anywhere to protect them. Laws need to protect Invertebrates that are under experiment, as well as those used outside the definition of experiment (and often outside the protection of the Law). The Laws to protect Invertebrates are weak. I enclose a link to a paper produced by the U.K. House of Lords and published on their website. It is dated 2009 but is still worth reading:
Here are the current details relating to the care of Cephalopods in U.K. laboratories:
This is a pro-experiment website but it does give details of the Law and codes of practice:
I also link to two excellent articles that Animal Aid have on their website:
I am totally against Zoos but there is some interesting information relating to Invertebrates here:
This is a good organisation that campaigns for Fish, dalso frequently mentioning Invertebrate animals who live in water:
There are “anaesthetics” that are sometimes used with Invertebrates. But I believe that most are merely agents that cause paralysis. Absence of movement does not mean absence of pain.
Again, there is a need for all animal rights organisations to stand together and work for the benefit of Invertebrates. Ideally, there is a need for an organisation to work solely for Invertebrate welfare and rights. I was out of animal rights campaigning for nearly 25 years. So I am a bit out of date with my research into animal rights. I should say though that Invertebrates across the World seem to be in much the same state (with regard to protection from abuse through legal mechanisms) as they were 25 years ago. I have been looking at some Scientific Journals and some Scientists in the Vivisection community still argue that there is no proof that Invertebrates feel pain. I think they are wrong. And they were wrong 25 years ago.
I close with a recent poem I wrote.
“My friend the Octopus”
I will never write a haiku about you,
For I will never truly know you
I don’t know what thoughts pass through your head,
But I know that you are intelligent and love games
That your memory is good
Some people say that you are ugly and strange. But to me, well…
In your own particular way,
Like when you are
Covered in flashing colours,
All over your body
And I watch entranced the pulses of light
The changes in texture,
You are beautiful
Too beautiful to eat or experiment on
Many find it hard, to empathise with you
Yet your Pain for it to work
Must be the same urgent vital thing that humans feel