G Kingdom Animalia Part 2

Phylum Echinodermata “spiny skin” Characteristics • • • • • • • • • • •

Most adult echinoderms have pentaradial symmetry (5 radii or multiples of 5) Free swimming larva Larva has bilateral symmetry Endoskeleton made of CaCOs plates called ossicles Ossicles may be attached to spines or spicules that protrude through the skin Water vascular tissue Tube feet aid in respiration, locomotion, feeding, excretion Nervous system but no brain Separate sexes (not hermaphrodites) No circulatory, respiratory, or excretory systems Deuterosomes: embryo developed anus before mouth

History • • • •

Fossil records: echinoderms dating back 500 million years, Cambrian Era Ancestors: sessile Modern: only 80 sessile species Echinoderms are deuterosomes, arthropods are protosomes (develop mouth first), chordates are deuterosomes; therefore echinoderms more closely related to chordates

Classification Class Crinoidea • Sea lilies, feather stars • Sessile; attached to rocks with a long stalk • Has upward-facing mouth • Arms contain sticky tube feet used to capture food & bring it to the mouth • Arms used for respiration Class Ophiuroidea • “snake-like” • Very long, flexible, narrow arms that move quickly • Ex. Basket Star o Has branched arms that form numerous coils & look like tentacles o Live on ocean floor beneath rocks & coral reefs o Use arms to rake in food o Use tube feet to capture food with mucus strands located in between spines

Class Echinoidea • “spine-like” “hedgehog-like” • Sea urchins o Test: compact, rigid, circular endoskeleton o Live on ocean floor o Move with tube feet o Aristotle’s Lantern: complex jaw-like mechanism; 5 teeth surround the mouth to scrape off algae from hard surfaces o Have spines that can be short & flat or long & thin or wedge-shaped o Some sea urchins have hollow spines that contain venom used for defence • sand dollars o short & broad o adapted for shallow burrowing o short spines for locomotion & burrowing o use tube feet to capture food that lands on its body Class Holothuroidea • sea cucumbers • live on ocean floor • use tube feet for locomotion • can crawl or burrow • armless • has small ossicles  soft (small) endoskeleton • tentacles: modified tube feet around the mouth that sweep up food • may eject internal organs through anus when threatened (called evisceration)

Starfish External Structures • top side: aboral surface • bottom side: oral surface • Central region: central disc • 5 arms covered in ossicles; protective spines • On the spines of each arm are tiny pincers called pedicellariae which clean the surface of any organism that might grow on it Water Vascular System • • Sieve Plate ↓ • Madreporite • ↓ Stone Canal ↓ Ring Canal ↓ Radial Canal ↓ Ampullae & Tube Feet

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System of water-filled canals connected at the end by tube feet Water enters through pore called madreporite Water travels down stone canal which leads to the ring canal From the ring canal, 5 radial canals branch away, leading to 2 rows of tube feet per arm Valves prevent backflow so water is directional At the end of each tube foot is an ampullae which are bulb-like sacs that are squeezed by muscles to force water into the tube foot When muscles relax water returns to ampullae, shortening or deflating the tube feet The inflation of tube feet allows for suction-cup method of movement Muscle contractions create hydrostatic pressure which in turn permits

movement Digestive System • Mouth on oral surface & is connected by a small esophagus to the cardiac stomach • Cardiac stomach can be evaginated (“expelled”) • Cardiac stomach passes food to the pyloric stomach • Pyloric stomach attached to the digestive glands on each arm • Cardiac stomach/pyloric stomach/digestive glands secrete enzymes to break down food • Food absorbed through the walls of the digestive gland • Sea stars eat clams, mussels, molluscs, oysters, worms, other slow moving animals o sea star clamps onto the clam & begins using to pull the clam open o the clam gets tired & opens a bit o sea star evaginates the cardiac stomach through the opening o cardiac stomach digests the inside of the clam o cardiac stomach is retracted

Other Body Systems • no circulatory, excretory, or respiratory system • fluid in the coelom bathes the organs & distributes nutrients & oxygen • gas exchange & waste excretion take place by diffusion through the thin walls of the tube feet & through the skin gills (hollow tubes that project from the coelom lining) Nervous System • no brain • central disc contains the nerve ring • nerve ring branches off into a radial nerve cord for each arm • if radial nerve is cut/damaged the arm it is specified for loses function • if ring nerve is cut, all arms lose coordination • nerve net controls the movement of the spines, pedicellariae, & skin gills • eyespot at the end of each arm that responds to light, touch, and chemicals Reproduction • each arm has 2 gonads (m) or ovaries (f) • females produce 200 million eggs each year • fertilization occurs externally • larva called bipinnaria o bilaterally symmetrical o free swimming • metamorphosis begins after ≈ 2 months • adult will have pentaradial symmetry • some species perform asexual reproduction by splitting at the central disc (see below) Regeneration • sea star can regenerate arms from the central disc • takes ≈ 1 year • defence mechanism • some species perform asexual reproduction by splitting at the central disc