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Echinodermata “Spiny Skin”
Gastrulation ¡ Gastrulation refers to how the embryo develops
germ layers and the gut.
¡ During development, animals form a ball of cells called a morula that eventually becomes a hollow ball of cells called a blastula.
Gastrulation ¡ The blastula eventually collapses upon itself
during gastrulation and forms three primary tissue layers called germ layers.
¡ The opening that forms as a result of gastrulation is the blastopore.
Gastrulation ¡ In Protostomes the first opening in the
blastopore becomes the mouth and a second opening eventually forms on the other side of the embryo to form the animal’s anus.
¡ Spiral cleavage
¡ (Proto = first ; Stoma = mouth)
¡ Examples: flatworms, annelids, molluscs
Gastrulation ¡ In Deuterostomes, the first opening in
the blastopore becomes the anus and a second opening eventually forms on the other side of the embryo to form the animal’s mouth.
¡ Radial cleavage
¡ (Deutero = second ; Stoma = mouth)
¡ Examples: echinoderms, chordates
Explain the embryonic characteristics that show how the starfish is more closely related to chordates.
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Phylogeny ¡ Deuterostomia is the branch of the animal
kingdom that includes echinoderms and chordates (vertebrate animals).
Echinoderm Characteristics ¡ radial symmetry
¡ Parts in multiples of 5 (pentamerism)
¡ no head or brain
¡ dermal endoskeleton made of calcareous ossicles
Echinoderm Characteristics ¡ water-vascular system
¡ tube feet provide movement
¡ hemal system for circulation of nutrients
¡ no excretory system
¡ separate sexes -dioecious
¡ regeneration of lost arms (parts)
Echinoderm Characteristics ¡ The top side(dorsal) is the aboral surface and the
under side (ventral) is the oral side
Endoskeleton
¡ Endoskeleton composed of calcareous plates or ossicles which are bound together by catch collagen.
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Endoskeleton
¡ Catch collagen can change from a liquid to a solid when stimulated by the nervous system.
¡ Thus, starfish can hold a certain posture for indefinite periods of time without muscular effort by solidifying the catch collagen. (saves energy)
Water Vascular System
Water Vascular System ¡ Water-vascular system (system of fluid filled ducts
and closed tubes)
¡ Water-vascular system is a unique structure designed for locomotion and food gathering.
¡ The madreporite pore takes in water and delivers it to a stone canal. Which then moves to the ring canal located around the mouth.
Water Vascular System ¡ Radial canals come
off the ring canal and run down the ambulacral groove.
¡ Lateral canals connect the radial canals to the dozens of tube feet which have suckers on the outer end.
¡ The system works hydraulically and can be quite strong.
Water Vascular System ¡ The groove that
runs along the oral side of each arm is the ambulacral groove.
¡ The ambulacral groove has a row of tube feet on each side with a radial nerve down the center.
Describe the path of water through the water vascular system:
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Digestive system ¡ Mouth is on the oral side. The large stomach is
located in the central disc.
¡ The large, lower part of the stomach can be everted through the mouth during feeding and most digestion is extracellular. (allows to consume more & longer)-Video
Digestive system ¡ The upper stomach is attached to a pair of
digestive glands called pyloric ceca (secrete enzymes and provide additional digestive areas to the intestine)that run down each arm.
¡ Sea stars are generally carnivores and feed on molluscs, crustaceans and small fish.
¡ The hemal system is thought to help with the distribution of digested nutrients.
Reproduction ¡ Most have separate
sexes.
¡ A pair of gonads lies in each arm.
¡ Fertilization is external and occurs in early summer.
¡ Gonads sometimes appear larger during the spawning season
Regeneration
¡ Sea stars can regenerate lost arms – even if all are lost. Regeneration may take several months.
¡ video
What lesson should the fishermen learn about starfish regeneration ?
Asteroidea
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Class Asteroidea (star – form) ¡ Sea stars or starfish usually with five arms with
equal share of organs, downward facing mouth.
¡ Central disc with tapering arms
¡ catch collagen to harden the body
¡ Examples: sea stars & starfish
Ophiuroidea
Class Ophiuroidea (snake-tail-form) ¡ Five arms are more slender and pronounced.
¡ Organs are confined to the central disc.
¡ Some can reproduce asexually by cleaving the central disc.
¡ ambulac;ral grooves are closed
¡ Examples: Brittle stars
Echinoidea
Echinoidea (hedgehog-form) ¡ They lack arms, ball or disk shape
¡ still have the basic pentamerous plan.
¡ Pedicellariae are spikes which may contain mild toxins
¡ omnivorous
¡ Examples: sea urchins, sea biscuits and sand dollars
¡ Video
Holothuroidea
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Holothuroidea (sea cucumber-form) ¡ They are elongated along the oral-aboral axis.
¡ soft-bodied
¡ crawl of the sea floor- hide under rock and burrow in the sand
¡ Examples: sea cucumber
¡ video
Other Vocab terms ¡ Podium/tube feet = foot like structure (used in
locomotion and eating)
¡ Central Disc = middle cavity compartment
¡ Stereom = meshwork structure of endoskeletal ossicles
¡ Oral = side of starfish that contain the mouth (ventral)
¡ Aboral = side of starfish that is opposite the mouth (dorsal)