This is from the DAN website:
https://www.daneurope.org/eng/faq1.htm
SEA URCHIN SPINE PUNCTURES
Q: 15 black sea urchin spines lesion of forearm. Swelling of wrist. What to do?
A: Some sea urchins have sharp venom-filled spines that can easily penetrate the skin. Others (found in the South Pacific) may have small appendages (pincers) that grasp victims and inoculate venom. Sea urchin stings are painful. If a person receives many wounds simultaneously, the reaction may be severe and cause extreme muscle spasm, difficulty in breathing, weakness and collapse.
Treatment
1. Immerse the wound in hot water to tolerance (43.3 to 45 C). This frequently provides pain relief. Other field remedies, such as application of vinegar or urine, are less likely to diminish the pain. If necessary, administer pain medication.
2. Carefully remove any visible spines. Do not dig around in the skin to try to fish them out - this risks crushing the spines and making them more difficult to remove. Do not intentionally crush the spines. Purple or black markings in the skin immediately after a sea urchin sting do not necessarily indicate the presence of a retained spine fragment. The discoloration more likely is dye leached from the surface of a spine. The dye will be absorbed over 24 to 48 hours, and the discoloration will disappear. If there are still black markings after 48 to 72 hours, then a spine fragment is likely present.
3. If the sting is caused by a species with pincer organs use hot water immersion, then apply shaving cream or a soap paste and shave the area.
4. Seek the care of a physician if spines are retained in the hand or foot, or near a joint. They may need to be removed surgically, to minimize infection, inflammation and damage to nerves or important blood vessels.
5. If the wound shows sign of infection (extreme redness, pus, swollen regional lymph glands) or if a spine has penetrated deeply into a joint, the injured person should be treated with an antibiotica by a qualified health professional, taking into consideration the possibility of a Vibrio infection.
6. If a puncture in the palm of the hand results in a persistent swollen finger(s) without any sign of infection (fever, redness, swollen lymph glands in the elbow or armpit), then it may become necessary to treat the injured person with a seven- to 14-day course of a non-steroidal anti-inflammatory drug (e.g., ibuprofen) or, in a more severe case, oral prednisone, a corticosteroid medication.
