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| Astolinto ★ |
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Echinoderms are a group of very different organisms. They live in the seabed (benthic), where they move slowly. They often have separate sexes (dioecious) but some species can reproduce by cleavage or be hermaphrodite. They lay the eggs. A small larva that swims freely, with bilateral symmetry, generally transforms into an pentaradial symmetry adult (the body is divided into 5 equal parts). All echinoderms have a particular skeleton that supports them (dermaskeleton) and a moving system that uses many small pedicels with a sucker (aquifer or ambulacral system). There are around 6000 species of echinoderms in all.
STARFISHES (ASTEROIDEA)
Starfishes generally have 5 strong squat arms. They are voracious predators of invertebrates that ingest with the mouth, present in the lower part of the body.
OPHIUROIDS (OPHIUROIDEA)
The ophiuroids are similar to starfish but have slender and mobile arms, used to crawl on the bottom. They have a distinct central disc. They are predators or feed on debris that they ingest with the mouth, present in the lower part of the body.
SEA URCHINS (ECHINOIDEA)
Sea urchins have a resistant armor covered with strong thorns. They feed mainly on debris or algae. There are almost 1000 species.
Quite common are Paracentrotus lividus and Arbacia lixula.
OLOTURIE (HOLOTHUROIDEA)
Sea cucumbers have an elongated soft body and feed on debris. They also live in the deep sea.
SEA LILIES (CRINOIDEA)
Sea lilies are animals attached to the bottom (benthic) that capture small invertebrates by filtration. They have five often feathered arms facing up. They comprise about 700 species.
Echinoderms
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