Spiny Urchin ate snail

[saltwaterdude]

I think my spiny urchin ate my mexican astrea snail. I saw it with its spines inside eating it.
Is this normal?
Also, are their spines really dangerous to the human touch?

 

[dundar]

I really don't know if thats normal, but the spines only are dangerous if you press on the urchin hard enough to have them puncture the skin. If the spines do break the skin and break off in the wound they can cause a nasty infection I know I stepped on one once, but they are not posionous.

 

[striker]

I just saw my long spined urchin devouring one of my mushrooms. For now I'm going to give him the benefit of the doubt that maybe it was sick and he was doing his job but if anything else happens he's out of there. He had his spines sticking into the mushroom during the meal. I guess this might be a way of them trapping or holding on to whatever they are eating.
I've never been stung by one so I'm not sure. In most cases I've witnessed my crabs, shrimps and urchins and stars will only eat or attack an animal when it is sick or dying. I suspect that the snail was on its way out and the urchin cleaned it up. One good point on the urchins and a reason why he's not flushed yet is that he cleaned up a batch of hair algae I had sprouting. They are very useful when it comes to keeping the tank clean.

 

[gliderpt]

Are these the same urchins that bump into LR and push it around?

 

[ophiura]

1) All urchins can plow around tanks and knock over loose rock or frags that are not properly attached. If you put one in your tank, you need to be prepared for it. They don't do this on purpose, it is the reality of having a bunch of unnaturally stacked rocks in a glass box, and then putting in a large animal that does not have eyes or a great deal of agility.
2) Why is there a long spined urchin in a 29 g tank? What are your plans when it gets large, which can be quite rapid? There is not much food in there for an urchin of this type. It is not a good choice for that size tank, IMO, if only because of its spines.
3) Urchins will often graze on just about anything in their path, though certain species are better known for this (eg pencil urchins). However, no one can account for the personality of an individual animal, so some may be more prone to this than others.
4) While a mushroom might be easier prey, I am a bit perplexed how a urchin could kill a healthy snail. Though I guess astreas could be on the smaller size. What size is this tank, and how much LR do you have?
5) The spines do cause problems, and you don't have to hit the spines very hard to have them puncture your skin. They break very very easily, and you need to be very careful putting your hand in the tank when you have a long spined urchin, just as if you had a lionfish in it. The spines are, obviously, defensive adaptations, and they can hold them very stiff as soon as the sense a change in shadows around them (as if a fish were coming in for attack). You need to know where it is at all times, which is why I am, again, perplexed at seeing them in such small tanks. Eventually, I guess some may have a good idea of what it feels like to be stung by them.
There are much better grazers for smaller tanks than these urchins.

 

[ophiura]

FYI, From Echinoderm Envenomations article, which makes numerous references to the Diadema aka long spined urchin:
From: http://www.emedicine.com/EMERG/topic158.htm
Long-spined urchins (Diadema species, Echinothrix species) are capable of causing deeply penetrating injuries. Envenomation initially results in severe burning pain, which is localized to the puncture site and may last several hours, reappearing with any pressure on the wound site. Localized edema, erythema, warmth, and bleeding may follow. The systemic symptoms of nausea, vomiting, paresthesias, muscular paralysis, and respiratory distress occur in the most severe cases. Delayed sequelae include wound tattooing as pigment is leeched from dark-colored spines into the surrounding tissue, synovitis if a joint space is violated, and secondary wound infection or granuloma formation if foreign material is retained.
I have only had a "pin prick" from one of these urchins, but there was still pain and the 'tattooing.' Can't imagine what a full blown pucture would be like.

 

[entice59]

my friend who used to work in the lfs hated them since he got one needle stuck in his finger while cleaning his tank, his finger swelled up good for a week. funny

 

[ophiura]

That one is from a bit of experience I am afraid
The tank we had them in was a little one, and there would be, like, 5 in there. Every one could sense when you were in there, and they would hold tight with their spines rigid. Really, you don't have to hit them hard at all (algae scrubbing in their was a P-I-T-A). When we had to get them out for people (less popular than getting a foxface or lion), spines would break off everywhere. You would have to carefully grab a longer spine and watch that you don't hit your other fingers against the remaining one...then the spine would break and you had to start over. They are hollow and delicate, the better to discharge venom with.
I have heard of fellow researchers getting more serious sticks from them, and am glad that I work on humble brittlestars.
On a different note, we once had a big cushion star come in (a fellow employee ordered it, and then couldn't pay up ). Now I was annoyed, because those things are supposed to be coral/sponge eaters, and I was delicately feeding it angel diet, etc. Then one day I walked past and the thing had a long spine urchin pressed against the glass and was eating it Very cool to see, if you aren't the guy losing money on the stock. I didn't make any effort to move the star, being happy it was finding yummy things to eat, including those urchins. It was a pretty thing, with a voracious appetite: