[Coral-List] help to ID encrusting critter

[Szmant, Alina]

Hello All:
 
We have been noticing for years a small purple 'colonial?' critter growing on the undersides of our settlement plates.  I have a few photos of them to see if any of you can tell me what they are.  These are small files to be able to send on Coral List, but I can send more and larger versions.  
 
They are very common and sometimes abundant; about 3 to 5 mm in diameter; have small purple/blue gramules in a clear gelatinous tissue matrix.  When they die they leave behind oval shaped skeletal congregates that appear chitinous in texture, and are made up of hollow tubes (no photos of all dead but can see a bit in one of them).  The overall 'colony' shape has a stadium dome-like shape:  higher tubules on the outer parts graded to low area in the center.  
 
I cannot see any zooid as I would expect for a bryozoan; no spicules as for a sponge; no tentacles; no siphons; not defined organs or appendages.  Colonial protozoan?  Any and all help would be appreciated.
 
Thanks,
 
Alina Szmant
 
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Dr. Alina M. Szmant
Coral Reef Research Group
UNCW-Center for Marine Science 
Presently in Field:  371 Bahia Dr, Key Largo FL 33037
Tel & Fax:  (305)453-4792
Cell:  (910)200-3913
email:  szmanta at uncw.edu
Web Page:  http://people.uncw.edu/szmanta
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