What are Sea Urchins?

About Sea urchins:

• They belong to a group of marine invertebrates called echinoderms, which means spiny-skinned animals. 
• It includes other well-known marine creatures like starfish and sea cucumbers.
• Habitat: They can be found in various marine environments, including rocky shores, coral reefs, seagrass beds, and sandy bottoms. They live on the ocean floor, usually on hard surfaces, and use tube feet or spines to move about.
• Appearance: Sea urchins are characterized by their spherical to somewhat flattened, spiny bodies.
• The largest urchin (known from a single specimen) is Sperostoma giganteum of deep waters off Japan.
• Features
  • They have a globular body and a radial arrangement of organs, shown by five bands of pores running from mouth to anus over the test (internal skeleton).
  • The pores accommodate tube feet, which are slender, extensible, and often sucker-tipped. 
  • They have a hard exoskeleton, or test, made up of interlocking plates or ossicles, which are often covered with movable spines.
  • From nodules on the test arise long, movable spines and pedicellariae (pincerlike organs); these structures may have poison glands.
• Food Habit
  • They are herbivorous, primarily feeding on algae and plant material.
  • They use their specialized mouthparts, called Aristotle's lantern, to scrape algae and other food sources from rocks or the seafloor.

Q1: What are invertebrates?

Invertebrates are characterized by their lack of a backbone or vertebral column. Instead, they have other structural features that support and protect their bodies. Invertebrates comprise a vast array of animal groups, including insects, spiders, crustaceans, mollusks etc

Source: Sea urchins fed waste cabbage to spare Japan's seaweed forests