Characteristics of Echinoderms
 Adult echinoderms have a body plan with five parts organized
symmetrically around a center
 Does not have an anterior nor posterior end or a brain
 Most echinoderms are two sided
 The side where the mouth is located is called the oral surface
 The other side is called the aboral surface
Characteristics of Echinoderms
 Five-part radial symmetry (Pentaradial)
 Internal skeleton - made up of hardened
plates of calcium carbonate
 The madreporite connects to a tube called the ring canal that
forms a circle around the animal’s digestive system
Characteristics of Echinoderms
Madreporite
Characteristics of Echinoderms
 Water vascular system – internal network of fluid filled canals
connected to external appendages
 Responsible for feeding, respiration, internal transport, elimination of
waste products and movement
 The water vascular system opens to the outside through a sievelike
structure called the madreporite
Characteristics of Echinoderms
 Suction cuplike structures called tube feet
 Attached to the radial canals
 Relies on the water vascular system
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When water is pushed into a tube foot the tube foot expands
When water is pulled out, the cup on the end of the tube foot shrinks (creates a
vacuum mimicking suction cups)
Feeding
 Carnivores like sea stars use their tube feet to pry open the shells of
bivalve mollusks (clams and scallops)
 Once the shell is opened the sea star flips its stomach out of its mouth
and pours out digestive enzymes into the prey’s own shell
 After dining, the sea star repositions the stomach back into its mouth
Feeding
 Herbivores such as sea urchins scrape algae from rocks using their five
part jaw
 Detritus feeders like sea cucumbers move like a bulldozer across the
ocean floor taking in a mixture of sand and detritus
Feeding
Circulation and Respiration
 Echinoderms need to exchange carbon dioxide for oxygen
 The thin walled tissue of the tube feet forms the main respiratory
surface
 In other species small outgrowth called skin gills function in gas
exchange
Circulation and Respiration
Circulation and Respiration
 The process of transporting oxygen, food and wastes are shared by
different systems in echinoderms
 Respiration (gas exchange) and the removal of metabolic waste occur
through the skill gills and the tube feet located all over the body, a
system to deliver oxygen and carry away carbon dioxide and other
wastes is not essential
 The distribution of nutrients is performed primarily by digestive glands
and the fluid within the body cavity
Circulation and Respiration
 Excretion
 Solid waste is released through the anus in the form of feces
 Excrete nitrogen containing cellular wastes primarily in the form of
ammonia
 Released where gas exchange occurs (tube feet and the skin gills)
Nervous System
 No head, has a primitive nervous system
 Have a nerve ring that surrounds the mouth and radial nerves that
connect the ring with the body sections
 Scattered sensory cells that are sensitive to chemicals released by prey
Nervous System
 sea stars have up to 200 light sensitive cells clustered in eyespots at
the tip of each arm
 Tells whether it is dark or light
 Many echinoderms hide under rocks in crevices by day (comes out
during the night to feed when most predators are asleep)
 Echinoderms are slow moving and are unprotected on one side
Locomotion
 Use tube feet and thin layers of muscle fibers attached to the plate
of the endoskeleton to move
 Mobility is determined by the structure of its endoskeleton
 Sand dollars have their plates fused together to form a rigid box
that encloses the animals’ internal organs
Locomotion
 These animals usually have movable spines attached to their
endoskeleton
 Combined with their tube feet they can crawl from one place to
another
 In sea cucumbers the loss of the plates makes the body very
flexible
Video
 https://www.youtube.com/watch?v=K2G7L5hcEt8
Reproduction
 Most echinoderms are either male or female
 Although some can be hermaphrodites
 The animals such as sea stars release their sperm and eggs into the
water
 The sea star detect the gametes of their own species and respond
by releasing their own gametes
Reproduction
 Fertilization occurs in the open water and larvae swim around
 The larvae which have bilateral symmetry swim to the ocean bottom
where they mature and metamorphose into adults that have
pentaradial symmetry
Regeneration
 Sea star can regenerate their limbs as long as their central part(core) is
not damaged
 Asexual reproduction called fragmentation
 Pieces of sea star with their central core intact can regenerate into a
completely new organism
Sea Stars
 Also known as starfish
 Many species have more than five arms
 sea star creep slowly along the ocean bottom
 Most are carnivores preying on bivalves they encounter as they move
Brittle Stars
 Live in tropical seas usually on coral reefs
 Resemble sea stars
 They have longer, more flexible arms allowing them to move more
rapidly across the ocean floor
Brittle Stars
 Has the ability to shed its arms when attacked
 The detached arm can wiggle resulting in a distraction for predators
 Are filter and detritus feeders that hide by day and wander
around in search of food at night
Sea Urchins and Sand dollars
 Found in almost all marine environments around the world
 Are grazers that eat large quantities of algae
 Other species are detritus feeders
Sea Urchins and Sand dollars
 Most sea urchins wedge themselves in crevices in rock during the
day and come out only at night
 Sea urchins have long sharp spines
 One type have small blue poison sacs covering the tips of each spine
Sea Cucumber
 Most are detritus feeders
 Found on the sea floors of oceans of great depths
How Echinoderms fit into the world
 Numerous in most marine habitats
 Sea stars are important carnivores that control the populations of
other animals
 Their numbers can rise and fall suddenly
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This causes major changes in the number of other forms of marine life
 Sea Urchins are important in that they control the population of
algae
How Echinoderms fit into the world
 Sea urchin eggs and sea cucumber are considered delicacies
 Echinoderms are easy to study as they produce large numbers of eggs
that are fertilized externally and develop in plain water
 Sea urchin embryos are studied for cell division and development
when drugs are applied