The body of the common starfish (or sea star) has five tapering arms which are broad at the base often slightly up-turned at the tip, when active. It possesses short white spines on the upper surface often in rows. It is usually orange, pale yellow or brown in colour, sometimes even red or purple, and has a cream underside. The lower surfaces of the arms have rows of small tube feet, used in locomotion and feeding.
Starfish move using small hollow tube legs. Each has a small sucker at the end and is controlled by muscles and a complex system of hydraulic tubes.
The common starfish feeds on mussels and other similar animals by prizing open their shell with their strong arms. Once the mussel becomes weak and opens its shell very slightly, the starfish’s stomach is inserted into the mussel’s shell dissolving their prey with digestive juices, before reabsorbing their stomach full of the ‘shellfish soup’.
Females produce small eggs that are released into the sea and fertilized externally to develop as tiny free-floating larvae. It has been estimated that a female starfish of 140 mm diameter can spawn 2.5 million eggs. This is important because only a small proportion of the eggs survive to become adult starfish.
- Diameter: 10-50cm
- Average Lifespan: 5-10 years
The common starfish is native to all British and Irish coasts, especially amongst beds of mussels and barnacles.
When to see
January to December
- Although they are named “starfish”, they are not related to fish at all. Starfish belong to the group of marine invertebrates called echinoderms (spiny skinned), which also includes sea cucumber and sea urchin.
- Starfish have the ability to regenerate different (missing) parts of their body. If a predator eats part of the starfish, one arm, for example, it will grow another.
- Starfish do not have a brain. They also do not have blood like other animals. Instead of blood, sea water circulates through their body delivering key nutrients and allowing its organs to function.
- The common starfish has eyes – just not in the place you would expect. There is an eye spot at the end of each of the five arms.