Download Echinoderms _Notes

Echinoderms
All Materials © Cmassengale
Phylum Echinodermata
Characteristics
 All marine
 Known as spiny-skinned animals
 Endoskeleton known as the test is made of calcium plates or ossicles with protruding spines
 Includes sea stars, brittle stars, sand dollars, sea urchins, & sea cucumbers
 Undergo metamorphosis from bilateral, free-swimming larva to sessile or sedentary adult
 Larval stage known as dipleurula or bipinnaria
 Adults have pentaradial ( 5 part) symmetry
 Lack segmentation or metamerism
 Coelomate
 Breathe through skin gills as adults
 Capable of extensive regeneration











Bipinnaria Larva
Ventral (lower) surface called the oral surface & where mouth is located
Dorsal (upper) surface known as aboral surface & where anus is located
Have a nervous system but no head or brain in adults
No circulatory, respiratory, or excretory systems
Have a network of water-filled canals called the water vascular system to help move & feed
Tube feet on the underside of arms help in moving & feeding
One-way digestive system consists of mouth with oral spines, gut, & anus
Deuterostomes (blastopore becomes the anus)
Separate sexes
Reproduce sexually & asexually
Includes 5 classes:
* Crinoidea - sea lilies & feather stars
* Asteriodea - starfish
* Ophiuroidea - basket stars & brittle stars
* Echinoidea - sea urchins & sand dollars
* Holothuroidea - sea cucumbers
Class Crinoidea
Characteristics
 Sessile
 Sea lilies & feather stars
FEATHER STAR
SEA LILY





Have a long stalk with branching arms that attach them to rocks & the ocean bottom
Can detach & move around
Mouth & anus on upper surface
May have 5 to 200 arms with sticky tube feet to help capture food (filter feeders) & take in oxygen
Common in areas with strong currents & usually nocturnal feeders
Class Asteroidea
Characteristics
 Usually sedentary along shorelines
 Starfish or sea stars
 Come in a variety of colors
 Prey on bivalve mollusks such as clams & oysters
Starfish Feeding on Clam



Have 5 arms that can be regenerated
Arms project from the central disk
Mouth on oral surface (underside)
STARFISH
Class Ophiuroidea
Characteristics
 Largest class of echinoderms
 Includes basket stars & brittle stars





BASKET STAR
Live on the ocean bottom beneath stones, in crevices, or in holes
Have long, narrow arms resembling a tangle of snakes
Arms readily break off & regenerate
Move quicker than starfish
Feed by raking in food with arms or trapping it with its tube feet
BRITTLE STAR
Class Echinoidea
Characteristics
 Includes sea urchins & sand dollars








SEA URCHIN
SAND DOLLAR
Internal organs enclosed by endoskeleton or test made of fused skeletal plates
Body shaped like a sphere (sea urchin) or a flattened disk (sand dollar)
Lack arms
Bodies covered with movable spines
Have a jawlike, crushing structure called Aristotle's lantern to grind food
Use tube feet to move
Sea Urchins:
* Spherical shape
* Live on ocean bottom
* Scrape algae to feed
* Long, barbed spines make venom for protection
Sand Dollars:
* Flattened body
* Live in sand along coastlines
* Shallow burrowers
* Have short spines
Class Holothuroidea
Characteristics
 Includes sea cucumber









SEA CUCUMBER
Lack arms
Shaped like a pickle or cucumber
Live on ocean bottoms hiding in caves during the day
Have a soft body with a tough, leathery outer skin
Five rows of tube feet run lengthwise on the aboral (top) surface of the body
Have a fringe of tentacles (modified tube feet) surrounding the mouth to sweep in food & water
Tentacles have sticky ends to collect plankton
Show bilateral symmetry
Can eject parts of their internal organs (evisceration) to scare predators; regenerate these structures in days
Structure & Function of Starfish
Body Plan
 Range in size from 1 centimeter to 1 meter
 Mouth located on oral surface (underside)
 Have an endoskeleton made of calcium plates
 Sharp, protective spines made of calcium plates called ossicles found under the skin on the aboral (top) surface
ABORAL SURFACE
 Have pedicellariae or tiny, forcep-like structures surrounding their spines to help clean the body surface
Water Vascular System
 Network of canals creating hydrostatic pressure to help the starfish move




WATER VASCULAR SYSTEM
Water enters through sieve plate or madreporite on aboral surface into a short, straight stone canal
Stone canal connects to a circular canal around the mouth called the ring canal
Five radial canals extend down each arm & are connected to the ring canal
Radial canals carry water to hundreds of paired tube feet

TUBE FEET
Bulb-like sacs or ampulla on the upper end of each tube foot contract & create suction to help move, attach, or open
bivalves

Rows of tube feet on oral surface (underside) are found in ambulcaral grooves under each arm
Tube Feet in Ambulcaral Grooves
Feeding & Digestion
 Tube feet attach to bivalve mollusk shells & create suction to pull valves apart slightly
 Starfish everts (turns inside out) its stomach through its mouth & inserts it into prey
 Stomach secretes enzymes to partially digest bivalve then stomach withdrawn & digestion completed inside starfish
Other Body Systems
 No circulatory, excretory, or respiratory systems
 Coelomic fluid bathes organs & distributes food & oxygen
 Gas exchange occurs through skin gills & diffusion into the tube feet
 No head or brain
 Have a nerve ring surrounding the mouth that branch into nerve cords down each arm
 Eyespots on the tips of each arm detect light
 Tube feet respond to touch
Reproduction
 Separate sexes
 Two gonads (ovaries or testes) in each arm produce eggs or sperm
 Have external fertilization
 Females produce up to 200,000,000 eggs per season
 Fertilized eggs hatch into bipinnaria larva which settles to the bottom after 2 years & changes into adult
 Asexually reproduce by regenerating arms