Ptilosarcus

Even though I said earlier that the jellies were my favorite cnidarians, these magnificent, flamboyant sea pens are also in the running. These are colonial Anthozoans, with a single large polyp specialized to support the colony from a central axis, and tiny feeding polyps dispersed along the margins of each "leaf." As in all members of this subclass (Alcyonaria), the gastrozooids have 8 pinnate tentacles.


These animals get to be over a foot tall and they live with the lower, fleshy part of the central poylp planted in soft sediment. And if their appearance in the bright aquarium lights is not thrilling enough, there's more. These animals can bioluminesce, sending eerie, blue-green waves of light along the colony.