It is not rare. Dark brown to black often with banded arms it hides under rocks in enormous numbers. Lift a rock in the low intertidal zone and you will see them. Dozens of brittle stars. Their long slender arms writhe as they scramble for cover. The common brittle star is one of the most abundant echinoderms on New Zealand's rocky reefs. Abundance is its strategy. Visibility is low. Survival is high. Under rocks and in crevices it hides during the day. The common brittle star is nocturnal. It emerges only after dark to feed. It wedges itself into gaps where predators cannot reach. During the day it is still and silent. Its arms are tucked close to its body. At night it unfolds. It stretches its arms into the water. Stillness is safety. Motion is risk. The cycle repeats. The arms are long and slender. They are capable of spanning fifteen centimetres. They are flexible. They coil around rocks and kelp stalks. When the brittle star moves the arms writhe like snakes. The disc is small. Only one to two centimetres across. But the arms keep going. They search for food. Proportion is skewed. Reach is extensive. Structure dictates movement. The body is minimal. The limbs are maximal. When threatened the arms break. This is a defence mechanism. A brittle star that is grabbed by a predator will shed the captured arm. It leaves the arm writhing in the attacker's grasp. The rest of the animal escapes. The arm regenerates within weeks. It is a costly defence. But it works. Sacrifice ensures survival. Loss is temporary. Regrowth is certain. The predator is distracted. The prey survives. Rocky reefs throughout New Zealand provide its habitat. The common brittle star lives from the low tide mark down to fifty metres depth. It occurs on reefs in harbours and in estuaries. It is found from Northland to Stewart Island. In warm northern waters and cool southern currents. It is one of the most widespread echinoderms in the country. Distribution is broad. Adaptation is general. Tolerance is high. The Māori name Pēwhā refers to its sinuous snake-like movement. The arms twist and coil. They move with a grace that seems impossible for an animal with no obvious muscles. It is a fitting name for a creature that seems to flow rather than crawl. Language captures motion. Name reflects form. The description is precise. The observation is accurate. Climate change may affect it indirectly. Warming waters and ocean acidification may impact the planktonic larvae that drift before settling. The common brittle star is resilient. But it has limits. For now it remains abundant under rocks. A writhing mass of arms when the rock is lifted. A vital part of the reef ecosystem. Resilience is tested. Limits are unknown.