Slime Star (Hymenaster sp.)

Close-up of a deep-sea slime star (Hymenaster sp.) at 2900 meters depth, off the coast of Oregon. Photo credit: UW/NSF-OOI/WHOI, Dive J2-1182, Dive J2-1182, V19

Hagfish aren’t the only marine species that have a slimy defense mechanism: Pterasterids are deep-water sea stars that can expel mucus to defend against predators, thus their common name: slime stars. They have a soft, inflated aboral surface with a hole in the middle (an ‘osculum’) that extrudes the slime when threatened (or collected by unwitting scientists).

We have observed pink slime stars in the genus Hymenaster at the deepest OOI site, Slope Base (2900 m), off the coast of Oregon. They are generally light pink and bumpy, and appear somewhat like raw chicken in texture. Unfortunately, there are 60 known species of Hymenaster with variable colors, shapes, and surface textures, and many of the diagnostic features used to identify them are either on the underside or inside the body, so the species ID remains unknown for now.