Primitive starfish, such as Astropecten and Luidia , swallow their prey whole, and start to digest it in their cardiac stomachs. Shell valves and other inedible materials are ejected through their mouths. The semi-digested fluid is passed into their pyloric stomachs and caeca where digestion continues and absorption ensues.  In more advanced species of starfish, the cardiac stomach can be everted from the organism's body to engulf and digest food. When the prey is a clam or other bivalve , the starfish pulls with its tube feet to separate the two valves slightly, and inserts a small section of its stomach, which releases enzymes to digest the prey. The stomach and the partially digested prey are later retracted into the disc. Here the food is passed on to the pyloric stomach, which always remains inside the disc.  The retraction and contraction of the cardiac stomach is activated by a neuropeptide known as NGFFYamide. 
Update 3/22: Tyler Ellis, an astronomy graduate student working with Tabetha Boyajian, updated Gizmodo via email this weekend to let us know that the follow-up response has so far been “pretty extensive.” For photometry (counting light particles being emitted in different parts of the electromagnetic spectrum) observers at the Los Cumbres Global Observatory and the KELT planet hunting network are viewing the star in optical, while the SWIFT ultraviolet space telescope, the Subaru telescope, and the Large Binocular Telescope are studying its infrared glow. Other collaborators are doing spectroscopy, trying to figure out which areas of the spectrum, exactly, are dimming. Still others are attempting to measure the polarization of light emitted by Tabby’s star, which can help determine whether the dimming is caused by something in the interstellar medium.
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