Description
Sea urchins (Echinoidea) are spiny aquatic animals belonging to the phylum echinoderms. Other well-known members of this phylum include starfish and sea cucumbers. There are approximately 850 species of sea urchins, commonly found in tropical waters and coral reefs, as well as in the Netherlands and Europe. They are also called sea apples, sea urchins, and sand dollars. Some sea urchins are venomous, but even without venom, accidentally stepping on one is unpleasant. The hollow spines are difficult to remove and can lead to infections. Sea urchins are usually between three and six centimeters in size. The smallest sea urchin grows to 6 millimeters, while the largest has a diameter of 36 centimeters. Sea urchins can be divided into regular sea urchins (Regularia) and irregular sea urchins (Irregularia).
