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Starfish sometimes have negative effects on ecosystems. Outbreaks of crown-of-thorns starfish have caused damage to coral reefs in Northeast Australia and French Polynesia. [59] [70] A study in Polynesia found that coral cover declined drastically with the arrival of migratory starfish in 2006, dropping from 50% to under 5% in three years.
A brachiolaria is the second stage of larval development in many starfishes. It follows the bipinnaria. Brachiolaria have bilateral symmetry, unlike the adult starfish, which have a pentaradial symmetry. Starfish of the order Paxillosida (Astropecten and Asterina) have no brachiolaria stage, with the bipinnaria developing directly into an adult.
In being multiple-armed, it has lost the five-fold symmetry (pentamerism) typical of starfish, although it begins its lifecycle with this symmetry. The animal has true image-forming vision. [3] Adult crown-of-thorns starfish normally range in size from 25 to 35 cm (10 to 14 in). [4] They have up to 21 arms.
The Royal Starfish is characterized by its bold colors. It has a purple granulated disk, which is the central region of the sea star, and the purple color continues to extend to its five arms. The margin of the sea star, which is its outline, is an orange color.
The variation ("polymorphism", in this case, a "color morph") most commonly found is pure blue, dark blue, or light blue, although observers find the aqua, purple, or orange variation throughout the ocean. These sea stars may grow up to 30 cm (11.8 in) in diameter, with rounded tips at each of the arms; some individuals may bear lighter or ...
Internal features can also show symmetry, for example the tubes in the human body (responsible for transporting gases, nutrients, and waste products) which are cylindrical and have several planes of symmetry. Biological symmetry can be thought of as a balanced distribution of duplicate body parts or shapes within the body of an organism.
Of all echinoderms, the Ophiuroidea may have the strongest tendency toward five-segment radial (pentaradial) symmetry. The body outline is similar to that of starfish, in that ophiuroids have five arms joined to a central body disk. However, in ophiuroids, the central body disk is sharply marked off from the arms.
They feed primarily on small crabs, though chitons, snails, clams, barnacles, brittle stars, and urchins have also been found in the diet. Their method of feeding is unique among sea stars. Rather than grasp their prey from below with their tube feet , they capture prey on their top surface using pedicellariae .