Sea urchin
Tripneustes ventricosus (top) and Echinometra viridis ( below)
The sea urchins ( Echinoidea ) ( from Ancient Greek ἐχῖνος echinos = hedgehog ) form one of the five classes, which belong to the tribe of echinoderms. There are live in all seas, invertebrates. The class is divided into 12 orders. To date, about 950 species are known.
Construction
Interior calcareous skeleton ( endoskeleton )
The outside of this skeleton is covered with an epidermis.
The actual, regular sea urchins ( Regularia ) are characterized by a hollow pentamer radially symmetric internal calcareous skeleton of calcium carbonate, which may be nearly spherical or more or less flattened according to the species of. It consists of the Apikalfeld top of the body, 5 double rows of Ambulakralplatten ( Ambulakralia ) and 5 double rows of Interambulakralplatten ( Interambulakralia ). The plates form irregular hexagons. The Ambulakralplatten ( the bright narrow bands in the figure) contain small holes ( Ambulakralporen ) from which emerge the Ambulakralfüßchen. The Interambulakralplatten carry only small spherical projections of the condyles of the spines.
The designated as irregular sea urchins ( Irregularia ) to which the sand dollar and heart hedgehog, are differ quite substantially from the regular sea urchins. Their skeleton is flattened dominated ( in the sand dollar disc- shaped) and not exactly radially symmetric, but by a bilateral symmetry. There is a front and back, a left and right and the movement always takes place to the front with a tendency. Sand dollars have no or extremely reduced spines, at the heart hedgehogs this more like a hair are formed.
Spur
The spines of the sea urchin sitting on small bumps and joints are partially movable by muscles. The formation of spines whose size, function, etc. can be very different depending on the type. In the regular sea urchins three main types are distinguished in the irregular even ten to twelve. The spines are mainly used for protection against predators such as starfish, snails, and large fish and release it when the sting even poison in some species, particularly toxic while the leather sea urchins (fire urchins ). There are sea urchins that burrow with their spikes into hard substrates such as coral reefs and rocks. Rarely driven with the spines food is captured. Inhabitants of the sandy soils use their spines also for locomotion. If you step on a sting, this cancels and may get stuck in the foot, which can lead to painful purulent inflammation. In some species the spines are also difficult to remove.
Pedicellariae
The pedicellariae are small pincer-like attachments that clean the surface of the sea urchin and can beat even larger attacker to flee with poison.
Coelomsystem
The interior of the sea urchin is through a series of tubular, fluid-filled cavities - divided - the Coelomsystem. Common to all the sea urchins Ambulakralfüßchen, thin tubes, which by pumping fluid ( hemolymph ) are moving.
Mouth apparatus
For grazing their food such as algae or nursery the sea urchins have a special Raspelapparat, the lantern of Aristotle.
Periprokt
The area around the anal opening is formed in sea urchins from multiple, irregularly arranged and calcareous plates called Analfeld or Periprokt.
Reproduction
The Sea urchins are dioecious. Egg and sperm are released in large quantities into the water. The plankton living, bilaterally symmetrical secondary larvae of sea urchins are called plutei (singular pluteus ). In sea urchins before Elba in the Mediterranean, the formation of reproductive groups was observed in about 40 m depth. In this case, several (10-30 ) individuals come together in one place, for the most part so close that they touch the spikes. In these groups, the egg and sperm cells are then simultaneously from many animals delivered, thus increasing the likelihood of successful fertilization significantly.
System
- Subclass Perischoechinoidea Order Lanz sea urchin ( Cidaroida ) Family: Cidaridae
- Family: Psychocidaridae
- Superorder Atelostomata order Cassiduloida Family: Apatopygidae
- Family: Cassidulidae
- Family: Echinolampadidae
- Family: Neolampadidae
- Family: Pliolampadidae
- Family: Asterostomatidae
- Family: Aeropsidae
- Family: Hemiasteridae
- Family: Palaeostomatidae
- Family: Pericosmidae
- Family: Schizasteridae
- Family: Calymnidae
- Family: Holasteridae
- Family: Pourtalesiidae
- Family: Urechinidae
- Family: Brissidae
- Family: Loveniidae
- Family: Spatangidae
- Family: Toxasteridae
- Order Diadematoida Family: Aspidodiadematidae
- Family: Diadematidae
- Family: Lissodiadematidae
- Family: Micropygidae
- Family: Echinothuriidae
- Family: Pedinidae
- Order Arbacioida Family: Arbaciidae
- Family: Echinidae
- Family: Echinometridae
- Family: Parasaleniidae
- Family: Strongylocentrotidae
- Family: Phymosomatidae
- Family: Stomechinidae
- Family: Saleniidae
- Family: Temnopleuridae
- Family: Toxopneustidae
- Order sand dollar ( Clypeasteroida ) Family: Arachnoididae
- Family: Clypeasteridae
- Family: Fibulariidae
- Family: Laganidae
- Family: Rotulidae
- Family: Astriclypeidae
- Family: Dendrasteridae
- Family: Echinarachniidae
- Family: Mellitidae
Use
In southern France, southern Italy, Greece, Morocco, Chile and Korea, as well as many other countries, the five gonads of sea urchins, raw or boiled in salt water, especially as an appetizer popular. In Japanese cooking the eggs of sea urchins are found as Uni on the menu.