Some kind of urchin and a trunk fish?

[DrSteve]

I saw both of these critters while diving in Huatulco (Pacific coast of Mexico). At first I thought this one was a dead urchin, but then when I nudged a shell it stuck in place and the whole thing moved. So the shells are stuck on for a reason and "deliberately." Perhaps a baby urchin? Didn't seem likely as it didn't have one of those obvious sack thingies sticking out. This picture was taken at 30-40 feet in a reef system and I saw a few on each dive.
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This one was taken in 15-20 feet in a rocky area very near to a shallow reef. I've never seen a fish with such a discontinuity apart from bottom dwellers and this one certainly doesn't look like a bottom dweller. This is the only one I saw.


Thanks!

 

[archman]

I don't know beans about species in that region, but urchin "decorating" is fairly common in certain genera, particularly short-spined types. Old experiments with (Lytechinus?) found a clear link between decorating and the urchin's photoreceptors. I guess they like "wearing clothes".

What are the "sack thingies" you are referring to as not being on this particular animal?

 

[DrSteve]

So it is likely some kind of urchin then. I'm wondering if it is specific to the Pacific as it isn't in the Carribean Reef ID guides...

Anyway, the sacky thing can be seen right in the middle of this banded urchin:

 

[DrSteve]

According to this web site:
http://www.wetwebmedia.com/urchins.htm
It could be a Toxopneustes pileolus or Flower Urchin. Indo-Pacific. Very toxic to touch. To 12 cm. in diameter. Shells, debris stuck on with its tube-feet.

 

[Starfish18]

Yep the urchin is definately a Toxopneustes pileolus or Flower Urchin.

 

[donnyb]

Well my guess, the fish is a male Ostracion,
possibly meleagris clippertonese ... the subspecies indigenous to that area.
I tried to find an image of the subspecies, but could not.
The dorsal pattern is not the same as our subspecies (camurum) here in Hawaii, which has white dots dorsally.