A brain.
Jellyfish have no ears.Jellyfish lack basic sensory organs and brain, but their nervous systems generally allow them to perceive stimuli such as light and odor.
Earthworms and cockroaches have nervous systems but no brain. Hydras have a nervous system consisting of a nerve net but lack a centralized brain. Amoebas do not have a nervous system or a brain.
Despite neither jellies nor sponges having central nervous systems, jellies have true tissues. The cells in jellyfish are also bound together, unlike in sponges.
No, not all living organisms have a nervous system. Invertebrates like sponges, jellyfish, and corals lack a nervous system, while all vertebrates, including humans, have a nervous system.
a backbone
Bones
Yes they do, invertebrates have small nervous systems, which consist of many small brains. Because of the anatomy of their nervous systems and the lack of neurons, they are thought to have limited cognitive capacity, and this means that they are likely to not be capable of emotions like we feel. This is why scientists are unsure whether or not or to what degree they feel pain.
Plants lack nervous system.
No, jellyfish are neither of these. The gastropods and bivalves belong to the phylum Mollusca, whilst jellyfish are Cnideria. Jellyfish are in many ways more primitive than molluscs, and lack many of their structural features.
Yes; jellyfishes have no head.
spine
No, they lack the body parts needed to preform that function.