Echinodermata Echinodermata

More documents

Recommendations

Info

Class Asteroidea (sea stars) • star-shaped, free moving, pentamerous animals • hollow arms project from a central disc • range from 2 cm to ~1 m in diameter • occur worldwide, largely in coastal waters • ~ 1500 species Asteroidea Water-Vascular System • consists of the hydraulic tube feet and internal coelomatic canals • canals: circumoral ring canal, radial canals, lateral canals, stone canal (opens aborally into a small chamber, madreporic ampulla, which joins the madreporite) • the WVS is lined by a myoepithelim and thus is ciliated and muscular Class Asteroidea (sea stars) • the mouth is located centrally on the underside of the disc (oral surface) • a large furrow (ambulacrum) extends radially from the mouth along each arm • each ambulacrum contains two or four rows of tube feet • the upper (aboral) surface bears an anus (when present) and a large, button-like madreporite (a sieve plae) Asteroidea Water-Vascular System Ampulla Ossicle Tube foot Sucker • each lateral canal has a valve and terminates in an ampulla and a tube foot (x40,000!) • the ambulacral ossicles form the floor of the ambulacral groove • longitudinal muscles of the ampulla contract => foot’s extension + attachment => longitudinal muscles of the foot contract => pulling force => detachment • adhesion is largely chemical, but adhesion by suction may also occur
Asteroidea Water-Vascular System • each lateral canal has a valve and terminates in an ampulla and a tube foot • the ambulacral ossicles form the floor of the ambulacral groove • longitudinal muscles of the ampulla contract => foot’s extension + attachment => longitudinal muscles of the foot contract => pulling force => detachment • adhesion is largely chemical, but adhesion by suction may also occur Asteroidea Digestive system • most of the space in the disc and arms is occupied by digestive system • the mouth opens into a short esophagus that leads to a large stomach • the stomach is divided by a horizontal constriction into a large, oral cardiac stomach and a smaller aboral pyloric stomach • pyloric stomach receives ducts from a pair of pyloric ceca in each arm • pyloric seca are elongate, hollow, branched extensions of the stomach Radial canal Tube foot Perivisceral coelom Pyloric cecum Pyloric stomach Anus Mouth Ring canal Cardial stomach
Page 1: Rubric for evaluating NEWS REPORTS,
Page 5 and 6: 3 Bilateral symmetry Anteroposterio
Page 7: NATURE | VOL 392 | 5 MARCH 1998 b C

Echinodermata Echinodermata

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?