Roatan critter ID help

[Dr MT]

See attached photos. These creatures are 2-3 mm. We found them in Roatan just off the wall between 10 and 100+ ft. Saw them last year Oct and Nov this year on several dawn dives. Behavior: Individuals in small scattered groups. They glow and pulse a bright blue (see photo with some pigment), when you get close (2-3 ft) they will flash/glow very brightly for about a second, the light goes off, the transulcent creature darts downward and away.

Entomologist @ home believes they are crustaceans.

 

[Rick Murchison]

Chiton???...
not sure which one.
on second thought, not a chiton...
checking...
Rick

 

[Trixxie]

Aren't those the guys from the space ship in the movie "The Abyss"?
(Kidding!)

 

[Rick Murchison]

Copepod! That's the name I was trying to dredge up from my failing memory. I believe what you have there is a large (relatively - there are some that are much larger, and zillions that are smaller) copepod, but I have no idea what species.
Rick

 

[Polpessa]

I think you may have photographed the creature responsible for the phenomenon we called "string of pearls" on Roatan, and they are called ostracods. For a cool pic of this, go to this site where I also found the following info:

Bonaire Talk: String of Pearls

This is actually the mating display of ostracods. Ostracods are tiny crustaceans, about the size of tomato seeds and they use their bioluminescence to attract mates in the same way that fireflies do. It’s a common phenomenon throughout the Caribbean and is usually best seen about one half hour after sunset or moonset. Male ostracods release their bioluminescent chemicals into the water as a string of dots. It’s a species-specific display - sort of a Morse code. The spacing of the dots in the water is unique to a particular species so females, recognizing the code for their own species, can swim to the end of a string of dots and know that they’ll find an eligible male. If you want to read a more scientific description of the phenomenon you can find it in:

Morin, J.G. (1986) "Firefleas" of the sea: Luminescent signaling in marine ostracode crustaceans. Florida Entomologist 69, 105-121.

 

[Papa_Bear]

I saw them doing their thing at Pillar Coral on the north side of Roatan on a flat calm night dive sitting in the sand with all the lights out in 20ft or so of water! One of the best light shows I have ever seen! Amazing! If you ever get the chance it is not to be missed! But the best way to see it is complete darkness! It looks like a disco with a million lights streaming from the ceiling! Very cool!

 

[archman]

Those are not ostracods. Ostracods possess a bivalved carapace that dominates the exterior anatomy.

I'll go with Rick's opinion as a copepod. As to which suborder, I'm not too sure. It's compact like a harpacticoid but the antennae don't seem *fuzzy enough*. And most harpacs don't swim, at least not very well.

Leslie probably knows this better than I do.