This star's arm tips are upturned, and no spines are visible on the animal's inflated outer surfaces. A pit or large pore located centrally on the star's dorsal side provides an exit for puffs of eggs and clusters of sperm during the summer breeding season. On the cushion star's underside are rows of yellow or orange tube feet encased in deep furrows running the length of the arms.
From the Bering Sea to California, cushion stars live in rocky habitats and grow to diameters of eight inches on a diet consisting primarily of encrusting sponges found in deep water. They also dine on sea squirts, bryozoans, hydroids, scallops, rock oysters and anemones.
Cushion stars are unusual in several ways. First, their planktonic young are non-feeders which develop with the aid of a yolk sac and settle down to a rocky sea floor after 10 to 12 days; a young star's mouth develops and bottom-feeding begins at about one month of age. Second, these stars are rather light sensitive, shying away from bright sunlight. Third, cushion stars secrete incredible amounts of mucus from their upper surface when disturbed — so much that a person might have a hard time touching the star's body through its bubble of slime. Another common name for the cushion star — slime star — reflects this strange defense tactic. Researchers have found the cushion star's slime to be highly effective in repelling predating morning sun stars ("Solaster dawsoni") and sunflower stars ("Pycnopodia helianthoides"). In one experiment, a clam was injected with cushion star mucus and subsequently was rejected as food by a sunflower star. Cushion stars make poor aquaria residents due to the toxicity of their mucus — the slime will kill snails, hermit crabs and sea cucumbers submersed in it for 24 hours.
Tide poolers occasionally find this star on exposed rocks in Eldred Passage and Jakolof Bay during extreme low tides. Keep an eye out for these rarely seen and fascinating marine invertebrates during the spring and summer minus tides along the bay's south side.
To learn more about the Kachemak Bay Research Reserve, please visit www.kbayrr.org.
Carmen Field is a naturalist and education specialist with the Kachemak Bay Research Reserve.
The Alaska Department of Fish and Game's Remote Video Escapement Recorder (RiVER) in operation at Delight Creek in East Nuka Bay, 2002.
Of the 26 species of sea stars identified in Kachemak Bay, perhaps the strangest of them all is the cushion star ("Pteraster tesselatus"). At a glance, this five-armed echinoderm appears rather normal — the upper, or dorsal, surfaces of its central disc and fat, stubby arms are adorned with variable patterns, sometimes star-shaped, of orange, gold and brown coloration. In fact, its Latin species name — "tesselatus" — means "regularly checkered" or "resembling a mosaic."
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