Common Starfish

• It can regrow lost arms completely, and an arm with part of the central disc attached can regenerate a whole animal.
• It digests its prey by pushing its stomach out of its own body.
• It feeds mainly on mussels and other bivalve molluscs.
• It is the most common starfish on European coasts, and also a problem for shellfisheries: it can decimate cultivated mussel and oyster beds.
• It opens bivalves by exhaustion: it grips the two valves with hundreds of tube feet and pulls relentlessly until the prey's adductor muscle gives way, which can take hours.
• And then it does not even open it fully: a gap of less than a millimetre is enough for it to push its stomach out through its mouth, slip it inside the shell and digest the prey within its own armour.
• It regenerates arms with ease, and it is common to see arms of different lengths on a single individual.
• It detects the presence of its prey by smell, and its prey likewise smell their predator: mussels respond to its scent by thickening their shells.
• It has suffered episodes of mass mortality in the North Sea, and it is studied as a sentinel species for the health of the seabed.

Skeleton type

Invertebrate - internal calcareous endoskeleton made of plates (ossicles)

Habitat and environment

Rocky, sandy and gravel bottoms of the North Atlantic, from the intertidal down to 650 m

Birth weight

A microscopic planktonic larva after external fertilisation

Size at birth

A microscopic planktonic larva that turns into a five-armed juvenile with short arms

Sexual maturity

Its 2nd year, on reaching ~5 cm across

Gestation / incubation

No gestation; several weeks of planktonic larval development after external fertilisation

Litter / clutch size

Millions of gametes released at each spawning

Sources consulted: MarLIN; SeaLifeBase; Diving Guru; EBSCO Research Starters; AnimalHub; Wikipedia (Common starfish); ScienceInsights; Plymouth Marine Laboratory (biology study)