What is this thing?

[JC Fedorczyk]

Can someone tell me what exactly this thing is? Found it on a blackbeard cruise. Didn't investigate other then taking the picture but the bright yellow and red marking caught my eye as we passed over it. Depth was at about 30ft during the day if that helps.

 

[archman]

Wow... I'm stumped. Do have a higher resolution image I can magnify?

 

[archman]

Just looked at the larger file you sent me. And your guess about it being a carapace sounds pretty solid to me. From the colour pattern, size, and tuberculate texture, I'd tag it as the abdomen of a molted scyllarid, specifically Scyllarides aequinoctialis (one of the "slipper lobsters").

I had various bizarre ideas in my mind... coastal Pacific chiton, live rock with the yellow boring sponge Siphonodictyon, live rock with an atypical serpulid tube... even a large isopod. The carapace notion never occurred to me.

Thanks for showing me something new! This is my favorite part of scubaboard!

 

[FredT]

Actually looks like the top of the tail section. The "v" forms a recognition pattern that can be seen as 2 dots poking out from under the carapace when the bug is "hiding". those two dots and the tiny purple antenne are the only reliable visual recognition patterns when the bug is in it's "blend into the rock" stealth mode. From the size of the "v" I'd bet on it being a small juvenile molt. Definetly a slipper though. They're good eating when you can get a large one.

FT

 

[archman]

Actually looks like the top of the tail section.

This one's tricky. Lay folks refer to lobster abdomens as "tails", but technically the tail is comprised of the uropods and telson only (flappy things at end and terminal medial segment). So from most folks' perspective it IS the "upper tail", and from the invert zoologists it's the abdomen. We're both right, but your "right" is more popular.

Dang, screwed again!

 

[JC Fedorczyk]

Okay so does that mean that I took a picture of an empty carapace or is it actually a juvenile lobster that just molted?

 

[archman]

Okay so does that mean that I took a picture of an empty carapace or is it actually a juvenile lobster that just molted?

Oops, I'm being vague myself. "Carapace" technically refers to the exoskeleton covering the head and thoracic segments only. The abdomen is not covered (unless tucked underneath the "carapace". But so many folks interchange "carapace" and "exoskeleton" (me included), the accuracy of the term degrades.

Anyways, that photo is missing the true carapace. It comprises the abdominal segments only. When the skeleton looks this "clean", its most likely that the critter molted it away, rather than was eaten.

And if Fred says it's a juvenile, I'd go with that. He's seen a lot more in the field than I have. The "V" thing is something I've never heard before...