Phylum Echinodermata

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Phylum Echinodermata
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General Facts

• Classified under the superphylum Deuterostomia
• Adult organisms have pentamerous symmetry
• They have a water-vascular system
• Ossicles Endoskeleton
• Found at every ocean depth
• 7,000 living species

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Water Vascular System
Only found in Echinoderms
Functions differ between species but general
functions include Locomotion, Attatchment,
Feeding etc.

• Water enters the
• madreporite.
• Flows through the
• stone canal.
• Then enters
• the circular ring
• canal.
• Water is then
• sent to the ampullae.

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Classes

• Crinoidea - Sea Lillies or Feather Stars
• Asteroidea - Starfish
• Ophiuroidea - Brittle Stars
• Echinoidea - Sea Urchins and Sand Dollars
• Holothuroidea Sea Cucumbers

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Class Crinoidea

• The first class to originate that is still around
  today.
• Live in depths anywhere up to 6,000m.
• Mouth is present on the top surface, usually
  surrounded by feeding arms.
• U-Shaped Gut
• Most crinoids have many arms but the basic
  five-fold symmetry can still be seen.
• Many have a stem as infants but not at adulthood.

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Crinoidean Physiology
Ambulacral Groove

• 3 Basic Sections
• Stem, Calyx and
• Brachials (Arms)

Anus
Pinnules
Ray
Interesting Fact About Motility Prior to 2005 it
was widely known that stalked crinoids could
move, but the fastest rate of movement recorded
was 0.6m/h. However on the seafloor off the
Grand Bahama Island a stalked crinoid was
recorded travelling at a speed of 140 m/h.
Calyx
Stalk
Cirri
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Class Asteroidea

• Around 1,800 sp.
• Typically have 5 arms but the number of limbs can
  differ even within a species
• Display pentaradial symmetry
• Water Vascular System (WVS) Unique to
  echinoderms
• Feed on shelled animals such as oysters and clams
• Have 2 stomachs
• Can regenerate arms

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Asteroidean Physiology

• Mouth located on the ventral surface
• Dorsal Surface is spiny
• Madreporite on dorsal surface
• Pedicellariae surround the spines
• Radial Canal Ampullae
• They have 1 microscopic eye on the end of each
  arm useful for detecting movement.
• Internally, they have a complex nervous system
  but lack a centralized brain.

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Class Ophiuroidea

• Body outline similar to Asteroidea
• Whip-like arms up to 60cm in length
• Around 1,500 sp.
• Most live below 500m
• However also commonly found on reefs

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Ophiuroidean Physiology

• Central Disc is sharply marked off from the arms
• The Disc contains all of the viscera
• Nervous system based in the central disc with
  radial nerves in the arms
• They have no eyes but can detect light and dark
  through the epidermis

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Class Echinoidea

• Relatively Small Test only 2-10cm across
• The biggest component in class enchinodermata
• Found all over the world
• Move slowly
• Feed mostly on algae
• They have a skin of moveable spines

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Echinoidean Physiology
Test Of A Sea Urchin

• Pentamorous symmetry
• can only be distinguished
• when looking at the test.
• Larval stage Crystalline bones build up the
  endoskeletan
• The fully formed spicule comprises of a single
  crystal.
• Aristotles Lantern The
• whole chewing organ

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Aristotles Lantern
Dorsal
The mouth is located on the oral surface of the
organism and is made up of 5 calcium carbonate
teeth and a fleshy tongue like structure within.
Oral
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Class Holothuroidea

• Usually scavengers.
• Evisceration Sticky cuvierian tubules entangle
  predators
• Replacement tubules grow back in 2 5 weeks
• Can live in very dense populations
• They have a single branched gonad
• An endoskeleton is present just beneath the skin

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Holothuroidean Physiology

• Tentacles Ensnare prey/sediment and transport
  it to the mouth.
• Respiratory trees hold water and oxygen is the
  extracted from the water and spread round the
  body in the hemal (circulatory) system.

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