spiny

Spiny is an adjective describing organisms or structures bearing spines—sharp, rigid projections raised from a surface. Spines occur across plants and animals and commonly serve defense or camouflage, but can also aid in shading or sensing the environment. In botany, spines are distinct from thorns (modified stems) and prickles (outgrowths of the epidermis).

In plants, spines are widespread in desert taxa such as cacti and some succulents. They reduce water loss by limiting air flow and provide protection from herbivores. Many spines are modified leaves; some spines are leaflets or branches that have lost chlorophyll and photosynthesis, though others can photosynthesize to a degree.

In animals, spines appear in various forms. Echinoderms such as sea urchins, starfish, and sea cucumbers bear calcium carbonate spines used for defense and sometimes movement. Mammals such as hedgehogs and porcupines have spines formed from keratinized hair that deter predators. Some fish, such as spiny dogfish, have sharp dorsal spines. In venomous species, spines can deliver toxins, as in certain sea urchins and venomous fish.

Etymology: the term derives from Old English spīn meaning thorn. The concept appears across many common names, including spiny lobster and spiny dogfish, which highlight prominent spines on these organisms.