The sea pen, Ptilosarcus gurneyi, is a colonial cnidaria in the same class as the anemone, the anthozoa. One polyp has been modified to form the body while the fringes of the "feather" contain numerous small feeding polyps.

Habital:

Sea pens are marine organisms: typically they are found living in a mud/sand substrate at least 3 inches (7.6 cm) deep. It is rare around Race Rocks, with a few individuals occuring on the North-West corner of Great Race Island. Note the small burrowing tubeworms in the mud around the organism.

Feeding:

The polyps feed on detritus, zooplankton (baby artemia), and possibly (according to The Reef Aquarium Vol. Two) phytoplankton.You should offer your Sea Pen Artemia nauplii, Daphnia, pulverized flake food, and detritus stirred up from the bottom of the tank.

Predator:

Predators of the sea pen are two nudibranchs, one the very large 3 inches(7cm) nudibranch, Armina californica and the other Mediaster aequalis, Rose Star Crossaster papposus and the Leather Star Dermasterras imbriacata.

Reproduction:

We don't know the reproduction of sea pens whether by sexual or asexual means.

References:

http://www.fishroom.com/library/seapen.html

http://www.lanecc.edu/science/zonation/seapen.htm