Phylum Phylum EchinoEchinodermatadermata“spiny” “skin”“spiny” “skin”

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Major Classes of Major Classes of EchinodermsEchinoderms

ECHINOIDEA: Includes the sea urchins and

sand dollars

ASTEROIDEA: includes the starfish (sea stars)

HOLOTHUROIDEA: includes the sea cucumbers

OPHIUROIDEA: includes the brittle stars

(below: a fossilized brittle star)

Characteristics of EchinodermsCharacteristics of Echinoderms• CoelomateCoelomate and and radially radially symmetricalsymmetrical• Body is usually Body is usually 5-rayed 5-rayed (pentaradial)(pentaradial)• Have a Have a calcareous skeletoncalcareous skeleton• Possess a Possess a water vascular system water vascular system used for used for gas gas

exchange, feeding,exchange, feeding, and and locomotionlocomotion• Complete Complete digestive systemdigestive system• Open/reduced Open/reduced circulatory system circulatory system ((no heartno heart)) with a with a

central ring central ring and vesselsand vessels• Simple Simple radial nervous system radial nervous system (no brain)(no brain)• Reproductive system consists of Reproductive system consists of gonadsgonads which which

take up a significant amount of space in the take up a significant amount of space in the body body cavitycavity

• Sexual reproduction Sexual reproduction with fertilization with fertilization outside outside body body (most)(most)

• Have Have ciliated, free-swimming larvaeciliated, free-swimming larvae• Abundant on most sea coasts, Abundant on most sea coasts, especially on rocky especially on rocky

shoresshores

Taking a closer look at Sea StarsTaking a closer look at Sea Stars• Possess Possess 5 or more arms 5 or more arms

which radiate from a central which radiate from a central diskdisk

• Mouth is Mouth is located on oral located on oral surfacesurface (underneath) (underneath)

• Sea stars are found all over Sea stars are found all over the world in a variety of the world in a variety of shapes and colorsshapes and colors

• Most possess a Most possess a simple light simple light sensitive eye spot sensitive eye spot at the end at the end of each ray (arm)of each ray (arm)

DigestionDigestion• Sea stars have Sea stars have 2 2

stomachsstomachs that perform that perform different functionsdifferent functions

1.1. The cardiac stomach The cardiac stomach can can be pushed outside of the be pushed outside of the mouth to engulf and mouth to engulf and digest food, then digest food, then digested food is brought digested food is brought inside to the pyloric inside to the pyloric stomachstomach

2.2. The pyloric stomach The pyloric stomach further digests food and further digests food and passes it on to the passes it on to the intestine and the anus intestine and the anus which is located on the which is located on the aboral surface (top)aboral surface (top)

This allows a sea star to This allows a sea star to consume food that would consume food that would normally not fit into its normally not fit into its mouth!!!mouth!!!

The water vascular system consists of a central ring and a series of canals that eventually end in tube feet which you can see protruding from the underside of this sea star. These tube feet are used for movement, feeding,

and bringing in water for gas exchange.

The Water Vascular SystemThe Water Vascular System

• Here are the tube feet of the sea urchin which Here are the tube feet of the sea urchin which protrude out from protrude out from the spines.the spines.

• Sea stars and urchins alternately Sea stars and urchins alternately contract muscles that force contract muscles that force water into the tube feet water into the tube feet which extends and pushes them into the which extends and pushes them into the ground. ground.

• The muscles are then The muscles are then relaxed in order for the tube feet to retractrelaxed in order for the tube feet to retract..

A Closer Look at Sea UrchinsA Closer Look at Sea Urchins

• Most sea Most sea urchins urchins possess possess spines of 1-3 spines of 1-3 cm cm but can but can be found up be found up to 20 cm to 20 cm longlong

• Globoid Globoid shape with shape with no rays or no rays or armsarms

• Have Have ball and socket joints ball and socket joints on the spines which allow on the spines which allow them to move. If you try to touch the spines of an them to move. If you try to touch the spines of an urchinurchin, , the surrounding spines will converge there.the surrounding spines will converge there.

• Possess a Possess a mouth with 5 calcium carbonate teeth mouth with 5 calcium carbonate teeth (see (see aboveabove). Also have a ). Also have a fleshy tongue fleshy tongue within. This within. This structure is termed structure is termed Aristotle’s LanternAristotle’s Lantern..

Sea Urchin mouth Sea Urchin Test (shell)

Defense systems Defense systems of Echinodermsof Echinoderms• Spines are observed on

many echinoderms and can be soft or hard and sharp. Their presence deters predators

• Pedicellariae are pincer-like structures that protrude from the body surface between the spines

• Pedicellariae keep the body surface clear of encrusting organisms

• Echinoderms also camouflage with their natural color into their environment

Ecological Roles of Ecological Roles of EchinodermsEchinoderms

• Starfish and brittle Starfish and brittle stars stars prevent the prevent the growth of algal mats on growth of algal mats on coral reefscoral reefs

• Ossified skeletons of Ossified skeletons of echinoderms are major echinoderms are major contributors contributors to many to many limestone formationslimestone formations

• Part of the food chainPart of the food chain, , larvae produce food for larvae produce food for other creaturesother creatures

• The death of The death of echinoderms often is echinoderms often is followed by followed by an increase an increase in seaweed growth and in seaweed growth and reef destructionreef destruction

• Sea urchin grazing Sea urchin grazing reduces the rate of colonization of bare reduces the rate of colonization of bare rockrock

• Burrowing of sand dollars and sea cucumbers depletes the Burrowing of sand dollars and sea cucumbers depletes the sea floor of sea floor of nutrients and encourages deeper penetration nutrients and encourages deeper penetration which increases levels of oxygen and ecological tieringwhich increases levels of oxygen and ecological tiering

• Sea urchins bore into rocks, releasing nutrientsSea urchins bore into rocks, releasing nutrients• Sea cucumbers provide Sea cucumbers provide habitats for parasiteshabitats for parasites• Echinoderms feed on Echinoderms feed on dead and decaying organismsdead and decaying organisms

Super Cool Super Cool Echinoderm FactsEchinoderm Facts

• Sea stars are capable of Sea stars are capable of regeneration of body regeneration of body parts as long as part of parts as long as part of the central disk remainsthe central disk remains

• The gonads of Sea The gonads of Sea urchins and cucumbers urchins and cucumbers are considered a are considered a delicacy in SE Asiadelicacy in SE Asia

• Sea cucumbers will Sea cucumbers will eviscerate eviscerate (shoot out (shoot out parts of their internal parts of their internal organs)organs) when they sense when they sense extreme danger, then extreme danger, then re-grow the organsre-grow the organs

• Sea urchins can Sea urchins can replace replace spines that are spines that are damaged or lostdamaged or lost