Ceratosoma tenue is not uncommon in the Marshalls, but seems to be found almost exclusively in the beds of Halimeda algae on the eastern lagoon slope of Kwajalein Atoll at depths from about 8 to 25 meters. The color of the animals vary from orange to almost maroon, always with purple spots along the margin and a few scattered on top. Specimens range in size from about 50 to 80mm, but a good chunk of that length is the long tail. We have also seen this in Hawaii.
There is considerable color variation between specimens.
These three rather small specimens were found together. The one on the right was eating a dark gray sponge that was so thickly embedded with sand and small rocks it was hard to see the sponge tissue.
In the photos below, the flap of the posterior dorsal margin that curls up and partly covers the gills (approximately the center of the body) is easily seen. This flap concentrates toxic defensive chemicals; probably those orange balls embedded in the edge of the flap are glands that produce or concentrate the toxins. Presumably a predator would be deterred after taking a bite of this, sparing the more sensitive and essential gills.
The two specimens below were found together (a few centimeters apart) on separate egg masses, but one egg mass was red and the other orange. What's up with that?
I like the red speckling along parts of the margin in the specimen below.
An 8mm juvenile.
Created 3 January 2006
Updated 16 July 2016
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