MCMURDO STATION, ANTARCTICA– In our webcast with John Weller recently, he showed some photos of a group of bat stars and close-up of the top of one of them. Bat stars are common sights on the bottom of Antarctic seas, clustering under holes and cracks in the ice where seals congregate. They scavenge seal droppings or bits of food left over from the seal’s fishy meals; nothing in the ocean goes to waste.

Photo (c) John Weller.

We were curious about the structures on the back of the little bat star (also known as a cushion star) so I wrote to my former advisor at U.C. Santa Cruz, John Pearse. Dr. Pearse did his doctorate scientific research in Antarctica on these invertebrate creatures whose scientific name is Odontaster validus. He emailed me back the other day and explained what was on the upper surface of the cushion star.

Photo (c) John Weller.

The pink flower-like structures are called paxillae and they create a space for water to circulate across the surface of the stars making it easier to absorb oxygen from the water. The purplish bud-like structures are called papulae, or “skin gills.” They extend from the inside of the star’s body cavity and have lots of tiny beating hairs, called cilia, that also help the animal absorb oxygen and get rid of waste products.

It’s curious that in such richly oxygenated water as found in the Ross Sea, these animals need two structures to aid their respiration. Dr. Pearse notes that there’s probably an interesting story there for some future invertebrate zoologist in Antarctica to investigate.