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Old 01/08/2018, 11:10 AM   #1
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"Sponge" Crab

I have been happily picking crabs off of my TBS live rock since I got it. Mostly I get stone crabs, which I put in the fuge or a separate tank. I have one Pilumnus sayi (I think!) in my fuge. I rather like crabs, and I do not have any serious bad experiences with them. It's fun to watch them grow.

Last night I pulled a tiny (less than 1 cm carapace) crab from my tank. I was ready to relocate it when I learned she is in a family way (she is holding a spongy gray mass of eggs under her that is almost as large as she is).

This little lady is white/gray/tan mottled with some hair (not as furry as a gorilla crab, but not smooth either). Her claws are even in size (unlike the stone crabs) and smaller - they lack the black tips of stone or gorilla crabs. Otherwise, she looks like a lot like a stone or gorilla crab (same body type). What crab could procreate at that tiny size?

I did not get a picture. I wound up putting her back in the tank because arthropod eggs = food for corals. I know where she hangs out in case I need to remove her (in the corner where the tang goes to poop).

I have some tiny crabs that live in my tubipora and keep it clean. They have never come out, but this could be one of them.

Does anyone have a similar experience or can offer an ID based on description? What are everyone's opinions on tiny crabs?

Thank you!

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Old 01/08/2018, 01:58 PM   #2
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It's very hard to ID crabs by description only.


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Old 01/08/2018, 08:36 PM   #3
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your tang poops in the corner too?!?!? I thought mine was litter box trained!

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Old 01/09/2018, 06:57 AM   #4
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Originally Posted by Sugar Magnolia View Post
It's very hard to ID crabs by description only.
I definitely understand this! I will try and get a photo. I'm not worried about exact species. I am more curious about what crabs are sexually mature with a one-inch carapace?

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Old 01/15/2018, 11:12 AM   #5
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Okay, I got some photos of her. She hid until she had her babies, but she has been out the last couple of nights. She likes to dig in the sand. She hangs out in that same corner and covers herself with sand when I shine in a flashlight. I've never seen her near the corals or any other inverts.

Again, she looks a great deal like a bad crab, but her body is only about an inch long and she is sexually mature. Also note the pinchers. For scale I included a pen - my hands are not that large.

Anyway, I'm too attached to get rid of her now, so I will keep in her own tank if she a bad guy or it she gets too big for comfort.

There must be several of these in my tank to be procreating. I've not gotten any new live rock in several months. Anyone else had tiny crabs with eggs?

Attached Images
File Type: jpg Tiny_Lady_2.jpg (30.1 KB, 47 views)
File Type: jpg Tiny_Lady_Fingers1.jpg (51.7 KB, 43 views)
File Type: jpg Tiny_Lady_Fingers2.jpg (43.1 KB, 49 views)
File Type: jpg Tiny_Lady_Scale_Pen.jpg (45.2 KB, 40 views)
File Type: jpg Tiny_Lady_Under.jpg (48.0 KB, 38 views)
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Old 02/15/2018, 09:06 AM   #6
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I hate to bump this after it died (I'm sorry!), but I am curious if anyone has any ideas?

For an update, it's still living in that same spot and has not grown. Still digs in the sand and comes out after dark. It's smaller than a hermit crab and has stayed far away from corals. It does not hide as much as the bigger pest crabs. It's from the Gulf (Florida/TBS rock).

Anyone had a similar experience? I love crabs and would be thrilled to be able to keep small ones in my main tank, but I am very skeptical of them.

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Old 03/16/2018, 01:08 PM   #7
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Both crabs look to be possibly in the same family

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Old 03/20/2018, 08:54 PM   #8
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Thanks for the response! I was thinking maybe xanthid (or something big and nasty) when I caught it the first time, but it has not grown at all. (I have pulled out a ton of assorted crabs out already, they are in another tank, getting huge!) This little lady continues to live in that one corner, make eggs, and stay tiny. She also lacks black claw tips. She is not as pretty as the ones in the linked photo (the purple ones). What crabs stay small and can reproduce at such a diminutive size?

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