Spine (zoology)

In a zoological context, a spine is a hard, needle-like anatomical structure. Spines are found in a wide range of animals both vertebrate and invertebrate.

In most spiny mammals, the spines are modified hairs, with a spongy center covered in a thick, hard layer of keratin, and a sharp, sometimes , tip.

Spines in mammals include the prickles of hedgehogs and the quills of porcupines as well as the prickly fur of spiny mice and Tenrec. They are also found on Echidna, a monotreme.

The ancient precursor to mammals, Dimetrodon, had extremely long spines on their backbone that were joined together with a web of skin to form a sail-like structure.

Many mammalian species also have penile spines.

The Mesozoic eutriconodont mammal Spinolestes already displayed spines similar to those of modern spiny mice.

Spines are found in the rays of certain finned bony fishes including scorpion fish. The sting that is found in a stingray is a type of barbed spine.

Spines are also found in invertebrate animals, such as sea urchins. They are a feature of the shell of a number of different species of gastropod and bivalve mollusks, including the venus clam Pitar lupanaria.
Spines are also found in internal organs in invertebrates, such as the copulatory spines in the male or female organs of certain flatworms.

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