In decapod crustaceans, the stellar ganglion seems to be the major "brain" controlling movement, if not sensitivity, it is usually much more developed than the two ganglia set above and below the oesophagus which are somehow anthropomorphically held as equivalent to a human "brain". Before taking tissue samples for histology preparations, I identify the location of the stellar ganglion below the cephalothorax and make a single one stroke incision. The effect is immediate, all activity of appendages stops, pereiopods fall placid. Destroying the perioesophagal "brain" has no immediate effect on motility. Similarly for extracting a lobster from its refuge under a boulder while scuba diving, inserting a steel hook externally and non destructively below the cephalothorax at the level of the stellar ganglion will usually allow to pull out the lobster without any resistance, I hypothesize that there may be an external effect on the ganglion mimicking some instance in mating.
I doubt that decapod crustaceans do not have thermal receptors. Identifying
water temperature is very important for a cold blooded decapod.
-In several species I have observed that females tend to actively move to warmer locations at the limits of a thermocline in order to hasten the development of the brood they carry.
-The preparation for molting is related to the accumulation of day degrees and molting events tend to be synchronized. Some migrations may be related to regulation of molting.
-I have tracked snow crabs bearing acoustic markers (allowing identification of their location) migrate into deeper water as the summer thermocline forms in Canadian fjords and deepens in a few days after ice break. They proceed by trial and error along a slope, moving up and down in order to identify the right temperature limit and thereafter progressively moving down as the the thermocline sinks.
Would somebody clarify what crustaceans may use as thermal receptors, whether these are external or internal?
Best wishes. Gerard Conan.
Les Watling wrote:
I think all these responses are pretty interesting. I agree mostly with Jens' cultural statement, but I would add the following comments.
This issue arises a lot here in Maine, the lobster capital of the US. We even had a faculty member make the unfortunate (in my opinion) statement that lobsters couldn't feel pain because they have no brain. Ah well. I think the issue has more to do with what, as has been pointed out, started with the Paramecium, or thereabouts. If we examine a lobster nervous system we find they have a three part cerebral ganglion complex, often thought of as a brain, typical of most crustaceans. The first part is mostly chemosensory, dealing with input from the antennae. The second part takes input from the eyes and eyestalks, and the third part integrates all the information coming from the remainder of the body. Much of this information is sensory, coming from a wide variety of receptors spread all over the body. Most people don't realize it, but lobsters, and all other crustaceans for that matter, have chemoreceptors and mechanoreceptors on all appendages and over most of the cuticle. There are other receptors, such as stretch receptors, and those embedded in muscles (proprioceptors) sending other information to the lobster's brain. There may well be receptors we don't yet know about, but to my knowledge there isn't a "thermoreceptor" in the lobster body, effects of temperature operating at a more molecular and physiological level. My guess about the pain issue isn't that it is pain as we know it, but rather, in these situations the lobster's sensory structures are all firing at once until they are deadened by protein denaturing (in the case of boiling water), or whatever other thing has happened to them. I suppose that cutting the ventral nerve cord would eliminate the passing on of information, thus eliminating the escape response (it would certainly eliminate appendage coordination!). Is it painful to have all sensory structures sending information to the brain? I can't say.
So, as Jens says, treating animals with respect is more important to us in many ways.
At 01:43 PM 1/27/2003, you wrote:
Great response, Larry!
For what it is worth, I would have to say that invertebrates must have some sort of discomfort sense (for want of a better term). It seems to me that the reason for pain no matter how it is perceived is to keep an organism away from a potentially harmful situation. You touch a hot stove; it burns, so you remove your hand from the stove, and it stops burning (eventually, anyway). I vaguely remember experiments waaaaaaaaaaaaaaaaay back in General Zoology at Junior College, where we added a drop of a chemical to a dish with Paramecium. If the concentration of the chemical was weak the Paramecium would plow right through it. If the concentration was strong, the Paramecium would approach, stop, reverse, and proceed in another direction. However, there was a mid-point concentration, where the stimuli was strong enough to stop the Paramecium, and cause it to reverse gears, but not change direction. So we had these little Paramecium going up to the drop, backing up, running into the drop again, backing up . . . for long periods of time. Back and forth, back and forth.
So, obviously the little Paramecium isn t thinking about the concentration of the chemical, and whether it is harmful or not, there is some other stimulation for the behavior. I see my fairy shrimps and tadpole shrimps avoid nets, or thrash when a predator bites them. I am certain that they do not feel pain as I understand it, but there must be something that elicits a negative response. I do not think that their nervous systems can provide them with pain the way we feel it. There must be some sort of discomfort sense or else they would have blundered into enough hostile situations that they would have been selected out.
D. Christopher Rogers
166 Buckeye Street
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Professor of Oceanography and
Pew Fellow in Marine Conservation
Darling Marine Center
University of Maine
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Phone 207-563-3146 x248
Gerard Y. Conan, M.Sc., Ph.D.
FAO (United Nations) Aquatic Living Resources Accredited Expert
Correspondant du Muséum National d'Histoire Naturelle, Paris.
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