Range: Marine waters throughout the world

Habitat: Sandy, muddy, rocky sediment

Size: Average about 6 inches (15 cm) in diameter

Diet: Sponges, bryozoans, hydrozoans, and more

Threats: Other sea stars

Lifespan: Unknown

Transcript:

Today on Animal Fact Files we’re discussing slime stars. Slime stars are also known as mucus stars, wrinkle stars, and cushion stars. There are over 100 described species in the slime star family, but what the heck is a slime star anyway? These invertebrates are a type of sea star. They look more puffy than most other sea star species, hence the name cushion star. Slime stars have a tent-like mantle suspended over the "true" surface of their body. This is held up by many spines giving them a honeycomb-like shape if viewed in a cross section. The space between their "true" surface, which looks like the surface of most other sea star species, and their fleshy, bumpy, sometimes wrinkly mantle serves multiple purposes. One of these is slime storage.

These animals earn their common name. When disturbed, slime stars let out a gelatinous glob of sticky, off-putting mucus. It's believed this mucus helps protect the invertebrates from predation. Perhaps surprisingly, these sea stars are predated by other sea stars, but if slime is involved any attacking echinoderms flee from the mucus. In turn, slime stars eat sponges, bryozoans, hydrozoans, and more. Like other members of their order, slime stars push their gut outside of their body and all over their meal in order to start the digestion process. As the animal is liquified, the slime star pulls its stomach back in along with the food it consumed. 

Slime stars live in marine waters throughout the world including polar regions. They can be found on sandy, muddy, or rocky substrate from tide pool habitats all the way down to the ocean's depths. Some slime stars inhabit waters deeper than two miles (3,200 m) below the waves! Most slime stars display five rays, which are sometimes called arms, but this isn't always the case. Even members of the same species can have different ray numbers. Some have six and a few others have been observed with eight rays! These invertebrates average about six inches (15 cm) in length across their entire body, that's including their rays, and they come in a variety of colors such as yellow, orange, cream, and brown. Upon close examination, a slime star's tube feet can be seen poking out from the bottom of their rays. These are used for locomotion!

Supposedly slime stars are soft. Their tent-like membrane makes them more snuggly than most of their hard-bodied relatives, if you can get past the mucus, of course. Apart from storing slime, the chamber between the membrane's surface and the slime star's true surface is used for egg brooding. Many sea stars spawn and their babies develop externally, but slime stars don't always do this. Sometimes, these animals retain their eggs inside their brood chamber and keep them close until they hatch. The female broods 30 to 40 eggs at a time and this happens throughout the year, though some sources note that certain species reduce their reproduction in spring. Only once the baby sea stars have fully formed, sometimes eating the internal flesh of their own mother in the process, are they released into the ocean. Slime stars have a pore on the top surface of their membrane through which the juveniles are pushed out, though some sources also note the babies may just burst through the mother's membrane Surinam toad style leaving their mother to heal once they've all dispersed.

It's unknown how long these invertebrates live, but one that they face is actually removal from water. If the pore in their membrane is open to air, an air pocket can form under the surface of the membrane making it impossible for the sea star to settle back on the sediment: the air bubble makes them float! 

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