E's break the spiral out of their shell

framptonbmx · Post by **framptonbmx** » Wed Jun 15, 2011 4:25 pm

Hey guys,

I had read a couple discussions on here in the past about Ecuadorians liking d shaped shells with the spiral broken out of them. I remember there was some debate over whether or not they found shells in this condition or if they created the shells themselves. I haven't been on here in a while, so I'm not sure if someone already discovered this. I had three E's switch shells recently and every one had been in a shell which I bought completely intact but all had the spiral broken out when the crabs switched out of them. I have no idea how they get the hole started, but they must pick it out piece by piece with one of their claws. I find it so fascinating. No wonder they all favor lighter shells (easier to break)

wolfnipplechips · Post by **wolfnipplechips** » Wed Jun 15, 2011 5:14 pm

It makes sense that they would modify it in that way.

I've been reading papers on the subject of shell selection in compressus, and in the laboratory, they actually prefer the thicker/heavier shells over thinner/lighter ones because one of their defenses is to curl up and roll down slopes. But their growth rate decreases with a heavier shell, so MAYBE to get around this trade-off between shell size and growth rate, they modify their shells from the inside. It's still thick on the outside for protection, but with the guts taken out, it is lighter, and they can maintain a good growth rate. Makes sense that if they had the ability to do this, they would.

I can't wait for my E's to change shells so I can check!!

A sentence from one paper I think is referring to the gutting of the shells: "There is also a preference for shells which have previously been used by other Coenobita individuals. This preference is due to shell modification by Coenobita, which increases the effective size of the shell."

Oooo! Here is the money!! "Several previous workers had noted that the shells occupied by crabs of the genus Coenobita often lack a columella (Ball, 1972; Kinosita and Okajima, 1968; Kurisand Brody, 1976). Kinosita and Okajima atribute this to mechanical and chemical abrasion, but do not report any experimental analysis of the phenomenon. Other modifications noted on shells occupied by Coenobita com- pressus were enlargement of the aperture of the shell, and in the case of Nerita scabricosta, wearing away of the ridge on the inner margin of the shell's aperture. The majority of shells occupied by Coenobita showed some sort of modification. All shells obtained from individuals with a dactyl length greater than 12 mm were modified. One of the major results of modification which could be measured quantitatively was the decrease in the weight of shells of a given length" It doesn't say that it was the crabs that did it, but I think it is implied if you read the paper, maybe. Hard to tell. From other quotes I have pasted here, you can see that the author does think the modification is from the crabs themselves.

I guess they did their own little experiment to see: "Ten individuals survived for two months, at which time the experiment was terminated. At that time, none of the shells occupied showed any signs of wear that could be perceived with the unaided eye. This suggests that the process of shell modification is quite slow."

If you (or anybody) wants me to send a pdf of this paper, please pm me with your email.

It's a good read!!

wolfnipplechips · Post by **wolfnipplechips** » Wed Jun 15, 2011 5:50 pm

I also have another pdf I can send that specifies that the shell modfication is to decrease weight (by up to 50%) and to increase volume so they can stay in there longer since shell competition is fierce and potentially lethal in many places. The other paper also says it, but not as directly.

Post by **wodesorel** » Wed Jun 15, 2011 6:55 pm

I've seen that last one as well.

I haven't been lucky enough to have any Es change out of shells that I knew to be intact, but I am waiting! They will move into already modified shells faster than you can blink though. I have a very large triton-type shell that my jumbo came in, that's very thick, and I really can't tell how she was wearing it down. It certainly wasn't from picking with her claws as the hole is very smooth. It's either from rubbing something against it or it's from a chemical means.

Wait! I have pics handy.

And two of the smaller shells in different stages of modification:

framptonbmx · Post by **framptonbmx** » Wed Jun 15, 2011 7:44 pm

Wow, so cool. It's a hard knock life being an E. Purple Pinchers have it easy just scooping up an turbo they find. The E's gotta do real work.

samurai_crab · Post by **samurai_crab** » Thu Jun 16, 2011 1:19 am

Well if you ever notice most C. clypeatus that come from the wild aren't in turbos. Turbos in fact I'd venture to guess aren't very common in the Caribbean. Most natural shell clypeatus I've seen come in Magpies, Apple Murex, and a few other shells I can't remember the name of currently. So this would allude to they prefer turbos, but since those aren't common in their habitat they take the next best thing. So while I'm not quite sure they have it easy when it comes to shells, its not a chore like it is for compressus, or so it would seem.

Its funny that thicker shells are mentioned because now that they are in my tank two of my compressus have picked up and seem to rather enjoy Florida King Crown shells, which are rather thin and light (probably why they took them). While not the greatest looking shells, they aren't bad to look at and they seem to fit smaller compressus rather well. My largest compressus won't change out of his store shell but the second largest readily changed shells a few times and seems to have settled on a roughly one inch opening white with tan moon shell. Its the largest I've seen and I can't seem to find anymore.

All my compressus thus far have been in a shell with no internal spiral, though the degree of wear/tear has varied. I have a nerite shell that the inside is completely gone and a few Thias like shells that still have a spike sticking out. Most shells I've removed that are missing the inside (debate for another thread).

Also anyone with great info on where to find more shells compressus like, such as the ones Wodesorel posted, the information would be greatly appreciated.

nibbler125 · Post by **nibbler125** » Thu Jun 16, 2011 1:45 am

i am always looking for a challange maby i should cut out the spiral of one of my spare shells and see if one of my crabs will go for it. i rember one of my Es went for a Babylonian shell but after a few hours he switched back into his old worn shell

Post by **wodesorel** » Thu Jun 16, 2011 2:47 pm

I've never found the choice E shells (the ones they come in from the beach) anywhere for sale. I'm guessing that the species have no value as a display shell, aren't good for eating, or are just hard to find to collect. (My guess is hard to find since you've seen the conditions of shells that Es wear.) However, even with leftover shells to change into, my Es still prefer Jade, Mexican (Pacific side, so native to the E territory), and Tapestry turbos.

Jade and Tapestry turbos are native to India, Indonesia, Africa, and down into Australia. Magpie (Pica) shells are in the Turbo family as well and are the native turbo species to the Caribbean. Magpie's don't offer a good weight to size ratio so the foreign ones we offer are much better!

samurai_crab · Post by **samurai_crab** » Thu Jun 16, 2011 11:45 pm

Ya, I do have a quite a few E's in Mexican Turbos now, odd how they like them in the tank, not so much on the beach, unless they are found in areas E's don't inhabit.

The ones they come in are nearly impossible, with the exception of nerites, but then I can never find them over like 1/2 inch opening and they usually have the full inside in them, which makes them really thick and the opening even smaller.

The one thing I would caution about breaking out the spiral on purpose is this (or at least my opinion), assuming the crabs are doing the modification and I think they are, breaking one out would probably not be the same as the crab doing it. They would either not find it comfortable, or I'd be worried about it being sharp.

tnt4eva · Post by **tnt4eva** » Fri Jun 17, 2011 12:27 am

I'm fairly certain that the C. variabilis (Aussie land hermit crab) does this too as the spirals were missing from almost all the shells of the Aussies I've bought.

They much prefer shells with the spirals missing to shells that are the same kind but with the spiral intact. As they prefer these shells, only a few have moved into shells with the spirals in tact, so I haven't yet had an opportunity to observe whether they actually take the spirals out, or if there is another species of hermit crab that does it and then the Aussies wear those shells when they find them.

Nerite and murex shells are the favourite. I've noticed that very large crabs can fit in quite small nerite shells with the spirals missing.

samurai_crab · Post by **samurai_crab** » Fri Jun 17, 2011 12:59 am

I have a nerite that is basically just a round opening inside because its completely gutted.

tnt4eva · Post by **tnt4eva** » Fri Jun 17, 2011 3:44 am

samurai_crab wrote:I have a nerite that is basically just a round opening inside because its completely gutted.

Same with the Aussies. After looking at pictures of the openings on some unmodified nerites, I'm sort of baffled as to how a land hermit crab could fit into some types of nerites if they weren't modified. They tend to have really restricted openings. The modified ones are usually a really snug, perfect fit.

Mama Crabs · Post by **Mama Crabs** » Fri Jun 17, 2011 12:37 pm

Recently I’ve read info on a forum that said that we should remove shells with the modified centers, has anyone heard this? Some blame them as being a source of death on the crabs. But if the crabs are doing it themselves, shouldn't is be accepted as being a good thing? I’m so confused!

samurai_crab · Post by **samurai_crab** » Fri Jun 17, 2011 1:02 pm

I've heard this too and what I think is, its a personal choice. It may be entirely accurate that shells missing the spiral can in fact injure the hermit crab. In the wild though given how rare shells for certain species of hermit crabs are, the increased risk might be worth having a home that fits and keeps you safe from outside predators. Its hard to say what would kill more crabs in the wild, missing spirals or having a shell that is too small/heavy. I would say overall though, assuming the crabs are modifying the shells, they have adapted to being able to survive in them and therefore most of the time they probably won't get injured on it.

samurai_crab · Post by **samurai_crab** » Sat Jun 18, 2011 12:25 am

I have something to add to this too. Sadly today as I was cleaning out the tank, removing old substrate and such, I found one of my E's that did not make it. She had just molted, since I found her exo and she wasn't hardened up yet. (Not entirely sure what went wrong, she didn't look stuck in the exo) Anyways, after removing her from her shell, a Florida King Crown shell, that I'm nearly 95% positive was completely intact when it went into the tank, I found that she had started wearing out the spiral. Now this wasn't even over a long period of time either, we got her back in October and sometime between December (she was in her old shell) and February (she is in her new shell) was when she changed. Now the type of shell she was in is a rather thin shell, so its easy to see how the thicker shells could take a lot long and like I said, I can't prove that the shell was intact but I'm 95% or more positive it was.

So I guess this was her parting gift to me, its sad to see her go, she was part of the second group of E's we got from a store near Cranberry, Pa. They came from horrible conditions. She was the last and longest living E we purchased from that store, I definitely will not be buying more crabs there.