Obelia sp.

The Obelia species shown here has a pale peach color with lighter-colored tentacles encased in a distinct wine glass shaped hydrotheca (glassy encasing).  The hydroid attaches to the substrate and creates stolons, however most of the growth is upright, perpendicular to the substrate.  Each stem of the hydroid may branch off into a series of polyps, each attached to their own branch.  The hydrostome (area around the mouth, in the center of the tentacles) is ball shaped.  The hydranth is trumpet-shaped when it is young and has not yet fully formed its tentacles.

Anatomy of Obelia

Hydranth- a feeding polyp which branches off from the main stem and has a mouth and tentacles
Tentacles- feeding extensions from the hydranth which may be covered with stinging cells to capture prey
Hydrotheca- a glassy encasing into which the tentacles of the hydranth can retract
Hypostome- the area around the mouth of the hydranth, in the middle of the tentacles
Obelia anatomy

Colonial Morphology of Obelia