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Chapter 16-The Echinoderms

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1 Chapter 16-The Echinoderms
Phylum Echinodermata- Spiny-skinned animals

2 Animal Development Acoelomate- An animal that lacks a coelom, or body cavity. Coelomate- An animal that has a body cavity in which the internal organs are located. Gastrula stage during embryo development- opening to the outside called a blastopore. Protostomes- Animals with mouths that develop from or near the blastopore; mouth before anus EX: Annelids, Mollusks and Arthropods Deuterostomes- Animals in which the anus develops from the blastopore; anus before mouth EX: Echinoderms and Chordates

3 Embryonic Development

4 Modern Echinoderms First animals to develop an endoskeleton
Marine, radially symmetrical as adults Evolved more than 650 million years ago Mostly free-living predators; some algae-eaters

5 Modern Echinoderms All Echinoderms share four fundamental characteristics: Endoskeleton- Calcium-enriched, spine-bearing, and composed of individual plates called ossicles Covered by a thin layer of skin which sometimes wears off Sometimes fuse for muscle attachment and shell-like protection Five-part Radial Symmetry- Mouth on bottom (oral), anus on top (aboral) Bilaterally symmetrical as larvae Arms, called rays, radiate from central point with no head or brain Can regenerate arms; Complete animal can regenerate from an arm connected to a portion of the central disk

6 Pentaradial Symmetry

7 Moving Sea Star

8 Modern Echinoderms Water-vascular system- Water-filled system of interconnected canals and thousands of tiny hollow tube feet Tube feet with suckers at each end extend outward through openings in ossicles;used to crawl; each is connected to a water-filled sac called an ampulla Water enters and leaves through pores in the madroporite- a sieve-like structure that filters out large particles Also functions in feeding and gas exchange- tube feet pull valves of bivalve open to exchange gas and excrete waste Coelomic circulation and respiration- Skin gills- Small, finger-like projections grow among spines to create an increased surface area through which gases can be exchanged Also function as excretory structures

9 Modern Echinoderms Nervous System Digestive system
Central ring of nerves branches into each arm allowing for independent movement Radial nerves run along each ray Eyespots- at tips of rays, detects light and dark Digestive system Uses water-vascular system to open bivalves Pushes stomach through mouth into shell (evisceration); enzymes digest solid food into liquid absorbed by the stomach Stomach is pulled back into mouth and food travels through intestines where nutrient absorption occurs

10 Reproduction Separate sexes Gametes located in arms (rays)
Sexual reproduction- external fertilization Larvae undergo metamorphosis – bipinnaria larvae

11 Body Structure

12 Echinoderm Diversity 20 extinct classes; 6 living
Super-class Stelleroidea Class Asteroidea Sea stars Carnivores Ossicles produce pincerlike structures called pedicellaria with their own muscles and nerves Snap at anything that touches them “Crown-of-thorns” sea star responsible for massive coral reef loss

13 Echinoderm Diversity Class Ophiuroidea Brittle Stars and Sea Baskets
Largest class Slender, branched arms that move in pairs Break easily They stay hidden in reefs and under rocks Filter feeders

14 Echinoderm Diversity Class Crinoidea Sea Lilies and Feather Stars
Most ancient and primitive Mouth is located on the upper, rather than lower surface Sessile Feather stars have hook-like projections to attach themselves directly to the ocean bottom or coral reef

15 Echinoderm Diversity Class Echinoidea Sea Urchins and Sand Dollars
Lack distinct arms Sea urchins found on the ocean bottom Sand dollars live on sand bars along coasts Spines provide protection and sometimes contain a venom Some sea urchins use paralytic toxins

16 Echinoderm Diversity Class Holothuroidea
Sea Cucumbers Soft-bodied, slug-like animals without arms Ossicles small and unfused Mostly separate sexes, some hermaphrodites Mouth surrounded by tube feet modified into tentacles covered with a sticky mucus Draws tentacles into mouth to clean off plankton and mucus Can release sticky threads from anus to trap attackers

17 Echinoderm Diversity Sea Daisies Discovered in 1986
Strange, disk-shaped animals with no arms Found off New Zealand coast Less than 1 cm in diameter Tube feet located around edge of disk rather than along radial lines

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