Ventral structure on G. smithii? ID help!

[andromedia226]

Hi! This is my very first post here, though I've lurked for a while. I have a month old cycled 12g SW to which I'm adding a G. smithii. He has a 2mm structure under its tail, between its pereiopods (under the middle pair). The structure appears almost like a tiny snail.

I believe this is a parasite because it does not share any similarity to its shell, but I'd like some input. Right now I'm manipulating the structure with a thin blunt wooden instrument, and it seems to move, and is fleshy underneath. I'd almost think that this was a blown-out bottom part of its carapace, but it's round like a snail and not flat like the rest of the carapace.

I'd appreciate any input anyone (including Dr. Roy!) can provide!
Thanks so much,
Mike

 

[Gonodactylus]

Great find! Without a photo, I'm guessing that this is a species of snail that specializes on gonodactylids. It is called Caledoniella montrouzieri. THey usually occur in pairs with the female setting between the last pair of walking legs and the much smaller male between the first pair of walking legs. Every now and then the female will wander back under the abdomen and deposit her large egg capsules on the gills of the stomaotpod. We don't know very much about the life histor of these snails, but I have found microscopic juveniles sitting under the shell of the mother. (We used SEM to seem them. We were actually trying to determine if the snail penetrates the shell of the stomaotpod. It does not appear to.) Ectoparasitized stomatopods usually do not molt or reproduce, although I had one G. smithii molt and when she did the egg capsules of the snail released veliger larvae. THis is something I would like to study, but we rarely find animals with these ectoparasites.

 

[andromedia226]

Thank you Dr. Roy for your help!

I thought you might enjoy some brief amateur observations:

I was able to watch the g. smithii at the pet store over the course of two weeks (small obsertavion time, but it's the best I could do) and noticed that it has a very strong penchant for favoring the ventral area, often laying on its carapace, ventral area upwards trying to reach/pry the snail off with its pereiopods. It spends large amounts of its time (~25%) doing this, and it has learned to brush up against rocks and rub itself. it seems that the most effective way for it to access the snail is to stand upright and reach under itself with one or two pereiopods.

The snail may be female owing to its large mass and middle-leg placement, but it isn't exactly medial placement - it's off center laterally by 1mm. This is a ~3.5" specimen of G. smithii.

The smithii seems more annoyed by the snail's presence than in pain, and other than a fondness for constantly lying on its back when not active (it's very active). It does not seem hampered by the snail in anything but perhaps swimming. When it swims, it arches its back outward in a U shape with the snail on the tangent of the curve. This behavior concerns me because I haven't determined if this is a voluntary of forced reaction to the snail's presence, or even just a favored position.

 

[Gonodactylus]

I take it that there is no sign of the small male which should be anterior to the female. The females often sit slightly to the side and often seem to have a small shelf that they have secreted.

Are there any egg sacks on the gills?

Roy

 

[andromedia226]

Also, if the C. montrouzieri is removed (aka forcibly crushed by either me or the mantis in nature) have you found that molting reinitiates?



I thought of some other questions I have, though most likely they're already in your logbook!

If this is a full grown G. smithii, then isn't it easy to date the duration of the presence of the C. montrouzieri by the size of the mantis' last molting, since they may not molt as a host?

Since the shell isn't breeched from the SEM, it doesn't sound like the snail has any parasitic abilities, do you know how it feeds?

It sounds like the snail merely uses the mantis for protection, transport and fertilized egg scattering - other than completely stopping the life cycle of the mantis (small cough), does this harm the mantis?

Will a small mantis stop growing in the presence of a snail?

Does this snail offer any symbiotic association with the mantis?

It sounds as though these snails grow from micro to macro entirely on the stromatopods, which sounds like they either attach as micro at grow to macro?

You also encountered a C. montrouzieri on a G. smithii - is there any pattern (other than native location) in the species of mantis that the snails inhabit? Are the differing actions/habits of any species conductive to aquiring this organism?

The mantis' reaction to the snail sounds a little like an isopod that inhabits the gill chamber of the sand shrimp, causing lack of molting and no reproduction.

Just some thoughts. I am strongly considering crushing the snail and waiting for it to detach after death. It might be a good way to see how the mantis reacts to a clean shell again - if it will start molting again (unlikely considering its size?) or reproducing (though I have no intention to do this). In any case, since the mantis seems not to enjoy any benefits from the snail's presence, I will likely crush the snail. I believe it to be too strongly attached to pry it off without harming the smithii.


Thanks for any input you can provide, and sorry about the long list of questions!

Mike

 

[andromedia226]

I removed the smithii and am checking the gills

 

[andromedia226]

There are no eggs in the gills and there is no male.

 

[sunce_22]

Dr. Roy! We have a 3.5 inch G. Smithii thich has these parasitic snails that you are talking about there. There is a male in the first pair of walking legs and a big female hiding in the swimmerettes (gills). There are also 20-30 white things on the gills aswell that we assume, due to the information in this thread, that they are the egg sacs. What can we do?

 

[Gonodactylus]

The white things are egg sacks. They will eventually hatch, but don't worry, they won't infect anything except other gonodactylids. My experience is that in the aquarium the snails eventually drop off and die and the stomatopod recovers. You could try crushing the snail with fine forceps, but if it were me, I would leave them alone. I was just on Heron Island and collected a few G. smithii. One female has the snails, only the second case I have seen in Australia. They are much more comon elsewhere in the Indo-Pacific.

Roy