Echinodermata Flashcards
What are the characteristic features of an echinoderm?
Five part radial symmetry evolved from bilateral symmetry
Calcareous mesodermal skeleton
Water vascular system
Describe the skin of the Echinodermata
Endoskeleton of calcium carbonate: ossicle
Consists of numerous small plates, covered by thin skin
Many small spines extend from the body
How do Echinodermata feed?
2 sides: arboral side contains anus and madreporite (connects ring canal to outside and helps replace water into water vascular system)
Oral side has mouth connected to esophagus
Most use water vascular system to procure food
Describe the Echinodermata circulatory system
Open circulatory system
Large coelom functions in both respiration and circulation
Water vascular system - derived from coelomic pouches
Water flows through small filter (madreporite) into ring canal and into radial canal (arms)
How do Echinodermata move?
Locomotion and feeding by means of tube feet
Bulb or ampulla squeezes water into tube foot
One way valve keeps water from flowing back out until bulb relaxes
Longitudinal muscles contract to pull animal along
Tube feet must be synchronised to allow for the animal to travel in the correct direction
Describe echinoderm respiration
Skin gills: dermal branchiae or papulae from coelom
Cloacal respiratory trees in sea cucumbers
Describe the echinoderm nervous system
No brain or CNS
Nervous system reflects a return to a sedentary lifestyle, radial symmetry
Consists of a simple nerve ring
Five branches from nerve ring source nerves to the five arms
Describe echinoderm reproduction
Asexual reproduction by splitting or fragmentation
Sexual reproduction by external fertilisation
Larvae are bilaterally symmetric, cephalised and reflect ancestral Echinodermata
Name the 6 classes of echinoderm
Crinoidea - featherstars and sea lilies Ophiuroidea - brittle stars Asteroidea - sea stars Echinoidea - sea urchins Holothuroidea - sea cucumbers Concentricycloidea - obscure group
Describe the class Asteroidea
Sea stars: arms not sharply distinct from central disc Ambulacaral grooves open Tube feet with suckers Pedicellariae present 1500 species Most have five arms and are important marine predators Superficial radial symmetry Can extrude cardiac stomach
Describe the class Crinoidea
Sea lilies and feather stars Arms branched attached by stalk or free moving Mouth and anus on oral surface No spines, madreporite or pedicellariae Food is filtered from water by branches and passed along to mouth by ciliary action 630 species Live at great depths >100m Tube feet modified for filter feeding
Describe the class Echinoidea
Sea urchins and sand dollars Skeleton rigid (plates fused) Mouth parts present Spines movable Ambulacaral grooves closed 950 species Lack arms Show 5 part radial symmetry Sea urchins feed by scraping algae off hard surfaces while sand dollars feed on organic matter in the sand as they burrow through it
Describe the class Ophiuroidea
Brittle stars 2000 species Arms distinct from central disc Ambulacaral grooves closed Tube feet without suckers, not used in locomotion Pedicellariae and anus absent Small and fast moving Carnivores, scavengers and filter feeders, most diverse group of Echinodermata
Describe the class Holothuroidea
Sea cucumbers
Elongated body with no arms, spines or pedicellariae
Skeleton only of microscopic plates, mouth ringed by retractile tentacles (modified tube feet)
1500 species
Superficial 5 part radial symmetry
Tube feet modified for filter feeding on plankton
Mouth surrounded by tentacles coated with mucus
Mucus traps tiny prey
Evert sticky tubules out their anus when threatened
What are the main points about the phylum Echinodermata?
Contains 7,000 species including the sea lilies, starfish, sea cucumbers and sea urchins
Eucoelomates: true body cavity
Deuterostomes: first opening in embryo is the anus
Lack cephalisation: no true brain
Only marine representatives
Grazers, scavengers or active carnivores
