WHAT A SPINELESS SPECIES
Animal species that do not possess a vertebral column or spine are invertebrates.
More than 98% of species on earth don’t have a typical backbone or notochord.
Examples of marine invertebrates include clams, snails, octopus, crabs and starfish.
In fact with the exception of a few vertebrates with a backbone such as fish, birds and mammals, all animals are considered as invertebrates.
This probably goes against your gut feeling - the main reason being that vertebrates are normally large creatures (needy of skeletal support).
They are therefore more visible to us, whereas most the widely ranging invertebrate group are smaller - often not visible for a range of reasons.
Many marine invertebrates comprise the beautiful sea slugs (really) the sea anemones; squirts; sponges and of course Jellyfish!