Transcript sea urchins, starfish, and their allies

Phylum
Echinodermata
Spiny-skinned animals:
sea urchins, starfish,
and their allies
General Characteristics
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Marine, Salt water based organisms
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Appeared in Cambrian period
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Pentameral
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Unique water-vascular system
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Bilateral and radial symmetry
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Echino-spiny Derma-skin
Example Organisms
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Sea stars
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brittle stars
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sea urchins
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Sea lilies
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sea cucumbers
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sand dollars
Embryology
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External fertilization
Eggs and sperm discharged into the
water
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Sea urchins brood their eggs
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no parental care
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Planktonic larval stages
Locomotion
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Most echinoderms move about
slowly
Short side branches lead to tube
feet
tube foot: thin-walled hollow
cylinder
base has a muscular ampulla
Locomotion (Cont)
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ampulla contracts the fluid and foot
is extended
muscles contract, shorten, and pull
organism forward
tube feet also enable it to hold onto
things
Anatomy of a Sea Star
Cross Section
View of Ambulacral Ridge
View of Radial Canal
Nervous System
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Radial, decentralized
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Central nerve ring surrounding gut
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Fiber tracts connect all radial nerves
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No brain and no specialized sensory
organs
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Sensory tissues located on 'feet'
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Can sense temperature, light, vibrations
Circulation and Respiration
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Based on water vascular system
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Filtration occurs in podocytes
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Gas exchange dependent on
environment: not very safe
Diffuses through skin (skin gills,
respiratory trees)
Circulation assisted by flagella
Brittle Star
Basket Star
Support
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A system of calcerous plates
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Some move, some fixed
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“Mutable” connective tissue; easy
to change rigidity
Sea Urchin Plate (bone material)
Tissue Organization
• Have a well-developed coelom in
which the various internal organs
are suspended, which includes a
complete digestive system, no
special excretory system, a poorly
developed circulatory system and a
nervous system with no brain
Tissue Organization (cont.)
• The water-vascular system is a
system of tubes (canals) filled with
watery fluid
• It provides assistance to a number
of systems in the animal and it has
a direct influence on locomotion
Digestive System
• The complete digestive system is
the most prominent of the organ
systems, which the digestive
system consists of a mouth with an
esophagus leading to the stomach,
which then leads to the intestines
Lantern of a Sand Dollar
Digestive System of Starfish
• Starfish have a mouth located at the
center of the lower surface which
leads to an esophagus then the
stomach ending with a short intestine
• The stomach is divided into two parts
where there are five pairs of large
digestive glands attached to it a pair
in each of the coelomic cavity of
each arm
Class Crinoidea
• Mouth faces upward
• Surrounded by many arms
• Sea lilies
• Feathered stars
• Approximately 600 species
Class Crinoidea
Class Asteroidea
• Five arms
• Double rows of tube feet on each
arm
• Mouth directed downward
• sea stars
• About 1,500 species
Class Asteroidea
Class Ophiuroidea
• Five slender, delicate arms or
rays
• Brittle stars
• Basket stars
• About 2,000 species
Class Ophiuroidea
Class Echinoidea
• Spherical, oval, or disk shaped
body
• Lacks arm but five-part body plan
• Sea urchins
• Sand dollars
• Approximately 900 species
Class Echinoidea
Class Holothuroidea
• Elongated, thickened body
• Tentacles around the mouth
• Sea cucumbers
• About 1,500 species
Class Holothuroidea
Excretory System
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Blastopore in the embryos becomes
the larval anus, where the larval
mouth is a secondary opening
Some forms preserve the larval
mouth as the adult mouth while
others reorganize the entire
digestive system during
metamorphosis where a new mouth
and anus forms
Basics
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Pentaradial symmetry in adults
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Water vascular system
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Calcareous internal skeleton
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Deuterostome embryology
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Complete gut except where
secondarily lost
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No excretory organs
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Diffuse nervous system