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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)