Phylum Echinodermata

The Basics

•Symmetry▫All echinoderms

have pentaradial symmetry

▫BUT… they develop from bilateral larvae

Body Openings▫Two, mouth &

anus

Classifying Characteristics

All echinoderms share several characteristics:

• Endoskeleton made of plates called ossicles. ▫ Ossicles attached to spines or spicules protruding through

the skin.▫ Enchinoderm = “spiny skin”

• Water Vascular System▫ Network of water-filled canals inside body

• Tube Feet▫ Small extensions of the water vascular system• Aid in – feeding, movement, respiration, excretion

• More closely related to Chordates than other Invertebrates▫ Develop as deuterostomes rather than protostomes▫ Larva develop with bilateral symmetry

Reproduction & Feeding:•Echinoderms reproduce sexually, with

both external fertilization & development.

•Echinoderms feed in many different ways:▫Carnivores, Filter Feeders, Scavengers,

etc.

Classification7,000 Species, 6 Classes

Class Asteroidia

• Name Means “starlike”: sea stars• Tube Feet are used in:

▫Movement▫Capturing Prey▫Gas Exchange

• Have TWO stomachs – Cardiac and Pyloric▫Digestion occurs in this order

:

Cardiac Stomach – Pyloric Stomach – Digestive Glands

• Remarkable Regeneration

Class Crinoidea

•Examples = crinoids▫Sea lilies, and feather stars

•Minimal movement▫Sea lillies are sessile as adults

Sea Lily

Feather StarClick Picture to See Video

Class Ophiuroidea

•Name means “snake like”

•Examples = basket stars & brittle stars

•Characterized by long narrow arms which allow quick movement. They will often break these arms off in order to escape a predator.

Basket Star

Brittle Star

Class Echinoidea

•Name means “spine-like”

•Example = Sea Urchins and Sand Dollars Click on the picture to view

Sand Dollar Movement

Class Holothuroidia•Name Means “water polyp”

▫When their tentacles are extended they resemble the polyp form of some cnidarians

•Examples = Sea Cucumbers

•Live on the sea bottom▫Crawl and burrow into soft

sediment

•Hairy Sea Cucumber Clip

Interesting Extras…• After watching ALL of the video clips, what did you

find interesting?• Watch this last Planet Earth Clip. What else can you

add to the list?

Importance:• Major part of food webs• Very sensitive to environmental changes, used to

monitor changes.• Food Sources: people consider urchins and

cucumbers delacacies• Medicine: Sea cucumbers are often used as a healing

agent.• Sea urchins release so many eggs, in fact, that they

are often used to study chordate development.

HW Questions:

1. Explain two reasons why echinoderms, in spite of their radial symmetry and simple bodies, are more closely related to chordates than to the rest of the invertebrates.

2. Starfish are known for their incredible ability to regenerate. Provide a logical explanation for why doctors are studying these abilities so closely.