As you can see from this list they are a morphologically very diverse group, at first it may not be obvious how they are all related, but despite their various forms they do all possess the characteristics outlined above.
General features Size range and diversity of structure Although most echinoderms are of small size, ranging up to 10 centimetres four inches in length or Phylum echinodermata, some reach relatively large sizes; e.
Among the largest echinoderms were some extinct fossil crinoids sea lilieswhose stems exceeded 20 metres in length. Although all living echinoderms have a pentamerous five-part radial symmetryan internal skeletonand a water-vascular system derived from the coelom central cavitytheir general appearance ranges from that of the stemmed, flowerlike sea lilies, to the wormlike, burrowing sea cucumbers, to the heavily armoured intertidal starfish or sea urchin.
The general shape of the echinoderm may be that of a star with arms extended from a central disk or with branched and feathery arms extended from a body often attached to a stalk, or it may be round to cylindrical.
Plates of the internal skeleton may articulate with each other as in sea stars or be sutured together to form a rigid test sea urchins. The surface of holothurians, however, is merely warty. Echinoderms also exhibit especially brilliant colours such as reds, oranges, greens, and purples.
Many tropical species are dark brown to black, but lighter colours, particularly yellows, are common among species not normally exposed to strong sunlight. Distribution and abundance Diverse echinoderm faunas consisting of many individuals and many species are found in all marine waters of the world except the Arctic, where few species occur.
Echinoids, including globular spiny urchins and flattened sand dollarsand asteroids are commonly found along the seashore. Although many species are restricted to specific temperate regions, Arctic, Antarctic, and tropical forms often are widely distributed; many species associated with coral reefs, for example, range across the entire Indian and Pacific oceans.
Many of the echinoderms of Antarctica are distributed around the continent; those with a floating planktonic larval stage may be widely distributed, carried great distances by ocean currents. Some species, particularly those in Antarctic and deep-sea regions, have achieved a wide distribution without benefit of a floating larval stage.
They may have done so by migration of adults across the seafloor or, in the case of shallow-water species, by passive transport across oceans in rafts of seaweed. Echinoderms tend to have a fairly limited depth range; species occurring in near-shore environments do not normally reach depths greater than metres.
Some deep-sea species may be found over a considerable range of depths, often from 1, metres to more than 5, metres. One sea cucumber species has a known range of 37—5, metres. Only sea cucumbers reach ocean depths of 10, metres and more. When present in large numbers, sea urchins can devastate sea-grass beds in the tropics, adversely affecting the organisms dwelling within.
Sea urchins that burrow into rocks and along a shore can accelerate the erosion of shorelines. Other tropical species of sea urchins, however, control the growth of seaweeds in coral reefs, thereby permitting the corals to flourish.
Removal of the sea urchins results in the overgrowth of seaweeds and the devastation of the coral reef habitat. Echinoderms can alter the structure of seafloor sediments in a variety of ways.The phylum Echinodermata contains organisms that share a specific set of characteristics, including spiny or bumpy skin.
There are five different classes of animals in the phylum: starfish, brittle stars, echinoids (which include the sea urchins and sand dollars), sea cucumbers, and sea lilies.
Echinoderms are usually intricate parts of their ecosystems. Many asteroids are keystone species. Sea urchins, if not controlled by predators, may overgraze their habitat.
Echinoderm is the common name given to any member of the phylum Echinodermata (from Ancient Greek, ἐχῖνος, echinos – "hedgehog" and δέρμα, derma – "skin") of marine rutadeltambor.com adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as sea stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone.
Echinoderm, any of a variety of invertebrate marine animals belonging to the phylum Echinodermata, characterized by a hard, spiny covering or skin. Select a different Surname Index Select a different Forename Index.
Oct 13, · In biology, a phylum is a division of organism (taxonomic rank) below kingdom (such as Animalia) and above class (such as Mammalia).There are 38 animal phyla, with nine phyla — Mollusca, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Echinodermata, and Chordata — making up the vast majority of all animals.