Now, none of the authors of the paper are marine biologists, so I can't expect them to know that this description:
A soft robot, composed exclusively of soft materials (elastomeric polymers), which is inspired by animals (e.g., squid, starfish, worms) that do not have hard internal skeletons.is technically not quite true. Worms at least don't have hard internal skeletons--A+ for that. Squid do have a stiff pen that keeps their mantle straight and gives their muscles something to work against, but it's made out of fairly flexible protein, so I'll give that a passing C.
But the starfish claim, unfortunately, has to get an F. If you've ever tried to dissect one, you know what I'm talking about. Echinoderms, the group that contains starfish and sea urchins, are actually well known (among invertebrate zoologists, anyway) for having an internal skeleton. In fact, it's item 1 on the list of distinctive echinoderm traits.
They're still invertebrates, because they don't have vertebrae, but they're full of crunchy bits called ossicles. Fused together in the case of the sea urchin, ossicles form those distinctive skeletons. (The skeletons are called tests, which is not the reason I started grading at the beginning of this post, although it would have been clever.)
(From http://www.flickr.com/photos/jurvetson/751085804/ Author: Steve Jurvetson)
But maybe the new robot follows the starfish plan even better than the authors realized. After all, it does have some internal hard parts--five actuators, which I believe only come in the "crunchy" variety.
Thanks to Judit P. for the article awareness!