Starfish: the bottom feeders

Starfish, also known as sea stars, are famous for their regenerative abilities and unique feeding mechanisms. Found on ocean floors, they are important predators and scavengers in water ecosystems.

Anatomy:

Starfish have a central disc-shaped body with five (or more!) arms reaching outward. Their underside, or oral surface, is covered in hundreds of tube feet. These feet are part of the vascular system, a hydraulic system that allows starfish to move and feed. Starfish have no brain, and their nervous system is decentralized, with a nerve ring around the mouth and radial nerves extending into each arm. Their unique feeding style involves extruding their stomach out of their mouth to digest prey externally, particularly bivalves like clams.

Evolution:

Starfish belong to the phylum Echinodermata, which also includes sea urchins and sand dollars. Early echinoderms were bilaterally symmetrical, but starfish evolved pentaradial symmetry (five-part symmetry) as adults.The ability to regenerate lost arms is one of the hallmarks of their evolutionary success.

Interesting Facts

1. Regeneration: some Starfish can even regenerate an entire new body from a single arm, as long as part of the central disc remains intact.
2. Multiple Arms: While most starfish have five arms, some species can have as many as 40 arms.