On rare occasions you may encounter this abundant midwater jelly near the surface.  The conical bell, diameter up to 5 cm, lacks pigment and is transparent.  A wide velum lines the inside of the bell margin.   With side lighting, birefringence of the bell muscles can create a beautiful array of colors as seen in the photo.  The stomach has 4 lips and lacks a gastric peduncle.   Look for 8 radial canals on which are attached the gonads.  The bioluminescent tentacles (usually 32) readily break free from the bell when the jelly is disturbed, probably as a defense against predators.  This species is commonly collected in midwater trawls, but invariably the tentacles have been shed.  Only surface-collected specimens will show the full complement of tentacles as in the photo here.  Colobonema is a strong swimmer with relatively powerful pulsing of the bell.  As is typical of Trachymedusae, this species is holoplanktonic (lacks an attached polyps phase), with each fertilized egg developing directly into a medusa.  It is among the more widespread and abundant of the deep-water Trachymedusae, with a maximum depth range between 500 and 1500 meters.  The distribution range does not extend into Arctic and Antarctic waters.   

All photographs © David Wrobel and may not be used or copied without permission!