merisiilejä

Merisiilit, also known as sea urchins, are marine echinoderms belonging to the class Echinoidea. They are characterized by their spherical or flattened bodies covered in a rigid, spiny shell called a test. These spines, which can vary in length and sharpness, are used for locomotion, defense, and sometimes for capturing food. Merisiilit are found in all oceans, from intertidal zones to the deep sea, inhabiting a wide range of habitats including rocky reefs, kelp forests, and seagrass beds.

Their mouthparts, located on the underside of the body, consist of a complex jaw apparatus known as Aristotle's lantern, which they use to scrape algae off surfaces. The diet of merisiilit primarily consists of algae, but some species may also consume small invertebrates or detritus. Reproduction in merisiilit is typically external, with males and females releasing sperm and eggs into the water column for fertilization. The resulting larvae are planktonic and drift in the ocean currents before settling to the seabed and metamorphosing into juvenile merisiilit.

In many cultures, merisiilit are considered a delicacy, and their gonads (roe) are harvested and consumed raw or cooked. However, their spines can deliver a painful sting, and some species are venomous, requiring caution when handling them. Merisiilit play an important role in marine ecosystems, helping to control algal growth and serving as a food source for various predators.