Phylum Echinodermata - Arapahoe High School

<strong>Phylum</strong> <strong>Echinodermata</strong>

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The Basics<br />

• Symmetry<br />

▫ All echinoderms<br />

have pentaradial<br />

symmetry<br />

▫ BUT… they develop<br />

from bilateral larvae<br />

• Body Openings<br />

▫ Two, mouth & anus

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Classifying Characteristics<br />

All echinoderms share several characteristics:<br />

• Endoskeleton made of plates called ossicles.<br />

▫ Ossicles attached to spines or spicules protruding through the skin.<br />

▫ Enchinoderm = “spiny skin”<br />

• Water Vascular System<br />

▫ Network of water-filled canals inside body<br />

• Tube Feet<br />

▫ Small extensions of the water vascular system<br />

• Aid in – feeding, movement, respiration, excretion<br />

• More closely related to Chordates than other Invertebrates<br />

▫ Develop as deuterostomes rather than protostomes<br />

▫ Larva develop with bilateral symmetry

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Reproduction & Feeding:<br />

• Echinoderms reproduce sexually, with<br />

both external fertilization & development.<br />

• Echinoderms feed in many different<br />

ways:<br />

▫ Carnivores, Filter Feeders, Scavengers, etc.

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Classification<br />

7,000 Species, 6 Classes

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Class Asteroidia<br />

• Name Means “starlike”: sea stars<br />

• Tube Feet are used in:<br />

▫ Movement<br />

▫ Capturing Prey<br />

▫ Gas Exchange<br />

• Have TWO stomachs – Cardiac<br />

and Pyloric<br />

▫ Digestion occurs in this order:<br />

• Cardiac Stomach – Pyloric<br />

Stomach – Digestive Glands<br />

• Remarkable Regeneration

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Sea Lily<br />

Class Crinoidea<br />

• Examples = crinoids<br />

▫ Sea lilies, and feather stars<br />

• Minimal movement<br />

▫ Sea lillies are sessile as adults<br />

Feather Star<br />

Click Picture to See Video

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Class Ophiuroidea<br />

Basket Star<br />

• Name means “snake like”<br />

• Examples = basket stars &<br />

brittle stars<br />

• Characterized by long<br />

narrow arms which allow<br />

quick movement. They will<br />

often break these arms off in<br />

order to escape a predator.<br />

Brittle Star

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Class Echinoidea<br />

• Name means “spine-like”<br />

• Example = Sea Urchins and<br />

Sand Dollars<br />

Click on the picture to view<br />

Sand Dollar Movement

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Class Holothuroidia<br />

• Name Means “water polyp”<br />

▫ When their tentacles are<br />

extended they resemble the<br />

polyp form of some cnidarians<br />

• Examples = Sea Cucumbers<br />

• Live on the sea bottom<br />

▫ Crawl and burrow into soft<br />

sediment<br />

• Hairy Sea Cucumber Clip

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Interesting Extras…<br />

• After watching ALL of the video clips, what did you find<br />

interesting?<br />

• Watch this last Planet Earth Clip. What else can you add to the<br />

list?

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Importance:<br />

• Major part of food webs<br />

• Very sensitive to environmental changes, used to monitor<br />

changes.<br />

• Food Sources: people consider urchins and cucumbers<br />

delacacies<br />

• Medicine: Sea cucumbers are often used as a healing agent.<br />

• Sea urchins release so many eggs, in fact, that they are often<br />

used to study chordate development.

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HW Questions:<br />

1. Explain two reasons why echinoderms, in<br />

spite of their radial symmetry and simple<br />

bodies, are more closely related to<br />

chordates than to the rest of the<br />

invertebrates.<br />

2. Starfish are known for their incredible<br />

ability to regenerate. Provide a logical<br />

explanation for why doctors are studying<br />

these abilities so closely.