Distribution

1. Potentially venomous species in the Indo-Pacific (D. setosum) and in the Caribbean (D. antillarum)
2. Indo-Pacific, including the Red Sea
3. Indo-Pacific, in the northeast as far as Japan (Toxopneustes pileolus and Tripneustes gratilla), as well as the Caribbean and the tropical and subtropical Atlantic coasts of South America and Africa (Tripneustes ventricosus)

Biology

Physical injuries from the spines of most sea urchins are possible, but only a few urchins are venomous.

The spines of Diadematidae are remarkably long (30 cm or more), hollow and filled with fluid. When they penetrate skin the spines break off easily. It has not been clarified whether this fluid contains toxic substances, but the severe pain that follows stings by these species are indicative of a toxic effect.

  Fig. 4.83 Diadema sp.

Echinothuridae only have short spines, the ends of which have a distended, vesicular form. Within this vesicle is a venom gland surrounded by muscle and connective tissue. When the spine penetrates the skin, the secretions are emptied into the wound.

Toxopneustes and Tripneustes species have only very short spines, which gives them a more compact shape. The body diameter of adult animals reaches 10–15 cm. Unlike the species discussed above, the venomous substances are not contained in the spines, but rather in so-called pedicellariae. These pedicellariae represent tiny gripping organs that are attached to the surface of the body by a short, mobile stalk and are present in large numbers scattered between the spines. They are a peculiarity of sea urchins and starfish; not only do they serve to clean the body surface, but they can also be used in defence in the form of venom apparatuses. Toxopneustes and Tripneustes species possess exceptionally large, venom-filled pedicellariae of the so-called globular type (Fig. 4.84). Their "heads" are composed of three claws that are held together at the base inside the stalk. The basal region of each group of claws is enlarged and contains a venom gland. The gland surrounds and opens into a claw composed of calcium carbonate, which ends in an inwardly curved spine with a venom outlet. By means of muscle contractions, the three claws can be moved towards each other and thus function like forceps.

  Fig. 4.84 Globiferous pedicellaria (adapted from Halstead 1988).

Envenoming can only be caused by those species that possess pedicellariae sufficiently large to penetrate human skin. This requirement is definitely met by some species of the Toxopneustidae. Their pedicellariae have a diameter of around 3 mm and a total length of 1 cm or more.

Risk

Injuries due to sea urchin spines are a common occurrence in ocean bathers. Apart from the physical injury, envenoming due to Diadematidae manifests itself through strong local pain, redness and sometimes swelling. Although rare, spines may sometimes penetrate a joint.

Echinothuridae stings apparently leave barely visible injuries, but are all the more painful. Systemic effects are unlikely.

Although some Toxopneustidae are considered dangerous, very few clinical reports exist. Apart from intense local pain, neurotoxic symptoms are also said to occur. Toxopneustes piloleus has been held responsible for several fatalities in Japan.

Treatment

Symptomatic, primarily prevention and treatment of infections. If broken-off spines stuck in the wound cannot be removed with forceps, it is better to wait until they come out spontaneously. This can be aided with the use of 2% salicylic acid cream, which softens the skin. Surgical removal of spine fragments from joints.

Literature (biological)

Cleland and Southscott 1965, Halstead 1971, 1988, Mebs 1992, 1995a, Williamson et al. 1996