OBJECTIVES• Describe the unique characteristics of Echinodermata.• State the classification of Echinodermata into five classes: - Class Asteroidea (Starfish, Asterias sp.). - Class Holothuroidea (Sea Cucumber, Holothuria sp.). - Class Crinoidea (Feather star). - Class Echinoidea (Sea Urchin). - Class Ophiuroidea (Brittlestar, Ophiura sp.).
PHYLUM ECHINODERMATA (Gk. Echinos, spine; derma, skin) A phylum of marine coelomate animals that are bilaterally symmetrically as larvae but show 5-rayed symmetry (Radial symmetry) as adults and have acalcareous endoskeleton and a water vascular system
Phylum Echinodermata: Echinoderms have a water vascular system and secondary radial symmetry● Sea stars and most other echinoderms are sessile, or slow-moving animals.● The internal and external parts of the animal radiate from the center, often as five spokes.● A thin skin covers an endoskeleton of hard calcareous plates.
● Unique to echinoderms is the water vascular system, a network of hydraulic canals branching into extensions called tube feet. – These function in locomotion, feeding, and gas exchange.● Water enters this system through madreporite.● From there it passes to a ring canal, which surrounds the mouth, & then to a radial canal in each arm.● From radial canals, many lateral canals extend into the tube feet, each of which has an ampulla.● Contraction of an ampulla forces water into the tube foot, expanding it.
● Sexual reproduction in echinoderms usually involves the release of gametes by separate males and females into the seawater. ● The radial adults develop by metamorphosis from bilateral larvae.
● All 7,000 or so species of echinoderms are marine.● They are divided into six classes: – Asteroidea (sea stars) – Ophiuroidea (brittle stars) – Echinoidea (sea urchins and sand dollars) – Crinoidea (sea lilies and feather stars) – Holothuroidea (sea cucumbers)
Class Main characteristicsAsteroidea • Five arms (sometimes more).(Starfish@ sea • Bear tube feet, which act like a suctionstar) disc, part of water vascular system. • Mouth generally lower (oral) surface of body, anus on upper (aboral) surface.
Holothuroidea • Elongated.(Sea cucumber) • Lack spines. • Hard endoskeleton is reduced. • Five rows of tube feet, part of water vascular system. • Some of the tube feet around the mouth are developed as feeding tentacles.
CLASS CRINOIDEA E.g. Featherstar
Class Main characteristicsCrinoidea • Attached to the substratum by stalked.(Sea Lilies) • As a group, they use their arms in suspension-feeding. • The arms circle the mouth.
Fig. 47.8 Class Crinoidea
• This is the oldest and most primitive of all classes of echinoderms.• The sea lily is attached to the substratum by a long stalk and thus sessile.• Sea lily is star-shaped, and posses long feather arms around the mouth (oral) which is on the upper side, and has no spine in its body wall.
CLASS ECHINOIDEA E.g Sea Urchin
Class Main characteristicsEchinoidea • Have no arms.(Sea urchin & sand dollars) • Have 5rows of tube feet that function in slow movement. • Sea urchins are roughly spherical while san dollars are flattened & disc shape.
Fig. 47.13 Class Echinoidea
• Sea urchin has no arm, but has five bands of tube feet.• Its body is spherical, and is covered with long spines.• The plates of the endoskeleton are fused to form a rigid structure.• The mouth is on the oral surface, and the intestine is long and coiled.
Source of picture:http://www.enchantedlearning.com/subjects/invertebrates/echinoderm/Seaurchin.shtml
Sand Dollar or Keyhole Urchin (Echinodiscus truncatus )Keyhole urchins body is covered with skin, muscle tissue,and short, fine spines that are used for burrowing. Rows oftube feet extend through holes forming the five "petals" onthe top side.
CLASS OPHIUROIDEAE.g. Ophiothrix sp.
Class Main characteristicsOphiuroidea • Distinct central discs, & the arms are long(Brittle star) & flexible. • Their tube feet lack suckers & move by serpentine lashing of the arms.
Fig. 47.12 Class Ophiuroidea
Source of picture:http://www.enchantedlearning.com/subjects/invertebrates/echinoderm/Brittlestar.shtml
Role of Echinodermata• Star fish- Threaten the coral reef.• Crown-of-thorns starfish (animal with venomous spines).• The only real predator of the dark starfish is the triton. But triton are being over- harvested, allowing the starfish to increase its numbers.• Because the main food of the crown-of-thorns starfish is coral, and the starfish population continues to grow, the coral reef ecosystem is being thrown out of balance.