Biology/Natural History: The entire central part (rachis) is said to be one large polyp. Smaller, inconspicuous polyps open into it and pump water in an out as needed for expansion or contraction. Produces a strong greenish luminescence when disturbed. Preyed upon by several nudibranchs, including Hermissenda crassicornis, Armina californica, and Tritonia festiva, and of the seastars Dermasterias imbricata, Pycnopodia helianthoides, Mediaster aequalis, and Crossaster papposus. The sea pens may rapidly burrow into the sediment when contacted by a predator. Although they do not appear to burrow when exposed only to seawater which contained a predatory seastar, they were more likely to burrow after contacting a predatory seastar if they had already been exposed to its smell. This species responds to different predators differently.