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

Characteristics of Echinoderms

Madreporite

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

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)

Characteristics of Echinoderms

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

Feeding

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)

Circulation and Respiration

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

Nervous System

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

Locomotion

https://www.youtube.com/watch?v=K2G7L5hcEt8

Video

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

Reproduction

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

Regeneration

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

Sea 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

Brittle Stars

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 Urchins and Sand dollars

Most are detritus feeders

Found on the sea floors of oceans of great depths

Sea Cucumber

Numerous in most marine habitats

Sea stars are important carnivores that control the populations of other animals

Their numbers can rise and fall suddenly

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

How Echinoderms fit into the world