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Animal lists · 12 entries

Animals Without Bones

Invertebrates — including insects, jellyfish, octopuses, worms and spiders — lack internal bony skeletons, representing roughly 97% of all animal species; sharks have cartilage rather than bone and are vertebrates, not invertebrates.

Updated 25 July 2026

Animals without bones are not a single group — they include at least 30 phyla with no shared ancestor more recent than the base of the animal tree of life. What they share is the absence of a vertebral column and internal bony skeleton.

Some invertebrates have hard external skeletons (insects, crustaceans), hydrostatic skeletons (worms, octopuses) or no skeleton at all (jellyfish). Sharks are sometimes mistakenly included but are vertebrates with cartilaginous rather than bony skeletons.

How this list was compiled

Entries are major invertebrate groups or representative species lacking an internal bony skeleton or vertebral column. Cartilaginous vertebrates (sharks) are noted as a common misconception but excluded. Support structures — exoskeletons, hydrostatic skeletons — are noted. Species count and ecological role are included where relevant.

Animals Without Bones

  1. Insects

    Exoskeleton (chitin); ~1 million+ species

    The most species-rich animal group. Hard external skeleton provides structure without internal bone.

  2. Arachnids (spiders, scorpions)

    Exoskeleton (chitin)

    Spiders, scorpions, mites and ticks. Exoskeleton moulted periodically for growth.

  3. Crustaceans (crabs, lobsters)

    Exoskeleton (chitin); some calcified

    Hard external skeleton, often calcified for additional strength. Moulted for growth.

  4. Jellyfish

    No skeleton; gelatinous mesoglea

    Among the simplest animal body plans. Structure from water-filled gelatinous tissue.

  5. Octopus

    Hydrostatic skeleton; beak only hard part

    Muscular hydrostat — muscles provide structure through fluid pressure. Only the beak is hard.

  6. Squid

    Hydrostatic; internal pen (chitin)

    Pen is a chitinous internal support rod — not bone. Muscular body wall provides main structure.

  7. Earthworm

    Hydrostatic skeleton

    Segmented body with fluid-filled coelom providing structure through hydrostatic pressure.

  8. Starfish

    Calcium ossicles; no main skeleton

    Scattered calcium carbonate ossicles in skin provide some rigidity but no central skeleton.

  9. Snail

    External shell (calcium carbonate)

    Shell is external calcium carbonate — not internal bone. Soft body without skeleton.

  10. Coral

    Calcium carbonate exoskeleton

    Colonial cnidarians deposit calcium carbonate skeletons. Individual polyps are soft-bodied.

  11. Anemone

    No skeleton; hydrostatic

    Soft-bodied cnidarians with hydrostatic body wall. No hard structures except nematocysts.

  12. Shark (cartilage, not bone)

    Cartilaginous skeleton — vertebrate

    Included because commonly mistaken for boneless. Sharks are vertebrates with cartilage rather than bone — not invertebrates.

Key facts

  • Roughly 97% of animal species are invertebrates — animals without internal bony skeletons.
  • Insects are the most species-rich boneless group, using chitin exoskeletons for structure.
  • Octopuses use a muscular hydrostat — fluid pressure in soft tissue replaces a skeleton.
  • Jellyfish and anemones have no hard structures at all — their shape is maintained by water pressure.
  • Sharks are vertebrates with cartilaginous skeletons — not invertebrates despite lacking bone.
  • Exoskeletons must be moulted for growth; endoskeletons grow continuously from within.

Animals Without Bones: frequently asked questions

What animals have no bones?
Invertebrates — insects, spiders, crabs, jellyfish, octopuses, worms, snails and many others. They represent roughly 97% of all animal species.
Do sharks have bones?
No — sharks have cartilaginous skeletons made of cartilage rather than bone. They are vertebrates, not invertebrates.
How do boneless animals support their bodies?
Through exoskeletons (insects, crabs), hydrostatic skeletons (worms, octopuses) or water pressure in gelatinous tissue (jellyfish). Each mechanism replaces internal bone.
Do octopuses have bones?
No. The only hard part is the beak, made of chitin. The body is a muscular hydrostat — soft tissue maintained by fluid pressure.
Are insects boneless?
Yes. Insects have chitin exoskeletons — hard external armour — rather than internal bones. The exoskeleton is moulted periodically to allow growth.
What percentage of animals are invertebrates?
Roughly 97% of described animal species are invertebrates. Vertebrates — fish, amphibians, reptiles, birds and mammals — make up the remaining 3%.

Sources

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