Sea stars, often called starfish, are typical marine invertebrate echinoderms and there are around 1,500 starfish species.
They are found on the seabed of many oceans including subzero polar waters and many of the world's tropics.
Somewhat surprisingly, sea stars exist in habitats from abyssal depths of 6 kilometers to less hostile environments of the inter-tidal zone (the area between high and low tide).
Starfish usually have five or more arms surrounding a central disc. Their arms, or tube feet, operate through a 'hydraulic movement system'. The mouth of a sea star is centrally located on its lower surface.
The lower part of the anatomy is known as oral and the upper surface is called aboral. Both the smooth and spiny aboral side of a sea star is often covered with brightly coloured overlapping plates. The upper surface displays various shades of red, blue, orange, or brown.
Starfish are filter-feeders. They feed opportunistically on benthic invertebrates which are bottom-dwelling organisms that live in sediment or sand.
Sea stars produce both sexually and asexually exhibiting complex life cycles.
The majority of these echinoderms can regenerate damaged or severed body parts and they can sacrifice an arm to survive capture.
Some starfish species are among the world's most invasive creatures. The tropical starfish Acanthaster planci, known commonly as the crown-of-thorns and the sea star of the northern Pacific are both considered as detrimental invaders with a devastating impact to delicate coral reef ecosystems.
Despite their unpopularity and destructive capabilities, starfish are believed to have existed for over 400 million years. They are seen as cultural curios and their symmetry is often copied in art and literature. Some species of starfish are toxic, and yet they are considered a delicacy and eaten in some countries.
Echinoderm Species |> Overview |> Crown of Thorns |> Sand Dollars |> Sea Cucumbers |> Sea Urchins