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Sea-urchins are mostly found in shallow water and along the shore, but species are also found at depths of 4500 m. Their body is usually ball or egg-shaped, more or less domed, rarely flattened and disc-shaped. There are two groups of sea-urchins, those with symmetrical near-spherical bodies, and those with usually oval bilaterally symmmetrical bodies. The spines may be long lances or short bristles, thin and with needle-points, or thick and blunt. They break easily and may be connected with toxic glands. Certain species of sea-urchins have venom organs (globiferous pedicellariae) which have calcareous jaws capable of penetrating human skin, but injuries from these are rare. Far more common are injuries by sea-urchin spines which can break off in the skin and give rise to local tissue reactions. |
Common injuries from sea-urchin spines usually belong
to the non-poisonous swallow water species Arbacia lixula (Linn.),
Sphaerechinus granularis (Lam.), Psammechinus microtuberculatus
(Blainville)
Paracentrotus lividus (Lam.). The long-spined Mediterranean species:
Centrostephanus longispinus has poisonous spines, but injuries from
this species are rare since the animals lives in relatively deep water
from 10 m.
Another echinoderm species which may possibly cause panic is the sea cucumber species Holothuria forskali Della Chiaje. When attacked or disturbed, this species extrudes long sticky whitish threads from the hindgut, the so-called "Cuvierian tubes". These threads contract to tighten but are easily removed.
Clinical Features: The spine of the non-toxic sea-urchin penetrates soft tissue giving rise to local tissue foreign body reactions. If not removed they may migrate into deeper tissues, causing a granulomatous nodular lesion, or they may wedge against bone or nerve. Joint and muscle pains may also occur, as well as dermatitis. Since dead or eaten sea-urchins shells are often left carelessly on the beach, injuries with old dead spines often occur. Injuries with thse spines is more likely to cause subsequent infection and also possibly tetanus in unimmunized individuals. Spines of the toxic species causes an immediate severe stinging or throbbing pain, which may stay at the site of the wound or spread throughout the body and last for several hours or days. There may be redness and swelling at the site of the sting, and the area may become numb, followed by muscle weakness and possibly paralysis. Death is rare.
Treatment: Sea-urchin spines should be quickly removed. Vinegar dissolves most superficial spines, and soaking the wound in vinegar several times per day and covering the area with a wet vinegar compress is usually sufficient; surgical removal is seldom necessary. If still present after days or weeks have passed, the spine may have migrated into deeper tissues. A bluish discolouration where the spine entered the skin will aid in locating the structure, which may sometimes be seen on x-ray. If the injury occurs on the shore through old spines, then prophylactic antibiotic cover must be instituted.
For poisonous species, the wound should be flushed with fresh or salt water, and then the affected area should be soaked in hot water or covered with a hot compress. The water should be very hot (circa 122 F), so that the heat will deactivate the poison. Continue applying hot water for 30 minutes to an hour. The patient should lie still with the stung part immobile and lower than the heart. Tie a venous tournique around a stung limb two or four inches above the sting. If the swelling reaches the band, tie another veroun tournique two or four inches higher up and remove the first one.
Pedicellariae stings are treated by washing the area and applying an analgesic and corticosteroid cream.
