I don't think there are animals without a skeletal unit. Yes there are animals without backbones; they're called invertebrates but as for an animal not having a skeletal unit, I don't think so. read more
However, some invertebrates do have an external skeleton, such as a shelled crab, shrimp, or lobster. Animals that live in sea shells are not considered exoskeletal. When you get to octopuses, squids, echinoderms, nudibranchs (sea slugs), jellyfish and so on, those are truly without skeletons. read more
There are more animals without skeletons than there are with skeletons! Invertebrate animals are those who have no skeletons. They include animals like mollusks, insects, and worms. Even sharks do not have a true bony skeleton, but have a cartilage skeleton instead. read more