Phylum Echinodermata

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Phylum Echinodermata
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Phylum Echinodermata

• Sea stars, brittlestars, basket stars, sea
  urchins, sand dollars, sea cucumbers, feather
  stars, sea daisys
• All marine
• 7,000 living species
• About 13,000 are known from the early Cambrian
  times

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Phylum Echinodermata General Characteristics
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Phylum Echinodermata General Characteristics
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• Specialized Structures
• Pedicellaria
• Papulae
• Spines

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Phylum Echinodermata 5 Classes

• Asteroidea
• Ophiuroidea
• Echinodea
• Holothurodea
• Crinodea

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• Seastars
• 1500 species
• Greatest diversity Northeast Pacific
• Live on sandy, muddy or rocky bottoms
• Occur world wide
• General body

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• General Anatomy
• Aboral Side (Dorsal)
• Madreporite
• Anus
• Oral side (Ventral)
• Mouth
• Ambulacral Groove

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• Water Vascular System
• Function
• Locomotion
• Circulation
• Fluid Volume Maintenance
• Parts
• Some feet have suckers

• All fluid movement is bidirectional

tube feet
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• Cardiac Stomach-can be protruded
• Pyloric Stomach-cant be protruded

• Ingestion
• Everts stomach through the mouth engulfs prey
  or tissue
• Releases digestive enzymes
• from digestive glands
• Sucks bolus into pyloric stomach
• Then into digestive cecae
• Digestion
• Completes in digestive cecae

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• Prey capture
• Prey
• Snails
• Bivalves
• Crustaceans
• Annelids
• Echinoderms
• Sponges
• Hydroids
• Corals
• Plankton
• Fish
• Also scavenge dead
• Senses prey chemically
• Attaches tube feet to prey
• Stiffens epidermis to act as an anchor for
  hydraulic feet
• Uses tube feet to dislodge or open prey valves or
  operculum.

Keystone Predator
Seastar Feeding
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• Nervous System
• Circumpharyngeal nerve ring
• Five Radial nerves
• Two nerve nets-one in dorsal part of the arm at
  the base of the epidermis and one in the ventral
  part of the arm

• Sensory
• At tips of arms
• Eyespots
• Sensory tubefeet
• Along body on epidermis
• Light, tactile, chemo

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• Asexual
• Fisson
• Regeneration
• As long as a portion of the circumpharngeal nerve
  ring is present
• Autotomize
• Sexual
• 10 gonads, two per arm
• External fertilization

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• Life Cycle

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• Circulation
• 3 inter-joined sets of vessels
• Hyponeural
• Supplies nervous system
• Gastric
• Supplies digestive system
• Genital
• Supplies gonads
• Each set
• Hemal ring around gut
• 5 radial vessels
• Vertical Axial Vessel connects all three sets and
  the heart

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• Sensitive to low oxygen
• Main respiratory organs
• Gills
• Tube feet
• Papulae

• Excrete nitrogen through tube feet and papulae
• Some materials are packaged into coelomoycytes
  which are found in the tips of the papulae
• Then exocytosis to remove waste.

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• Brittlestar and basketstar
• Largest class 2,000 sp.
• Lives in the subtidal zone and deep soft sediment
  
• Arms look segmented but not
• Occurs world wide
• Disk 1-12cm
• Some 1 m!

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• No pedicillaria
• Epidermal chromatophores
• Disk
• Ossicles may be present as shields
• Jaws

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• Arms
• Oral side
• No ambulacral groove
• Aboral side
• Cross section
• Arm solid!
• Suckerless tube feet

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• Water Vascular System is similar in form and
  function to the asteroids
• Nerve ring same also
• Cirumpharygeal nerve ring

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• Locomotion
• Most agile echinoderms
• Similar motion with tube feet but arms have
  better musculature and are not as massive.
• Some can burrow
• Involves more rowing, swimming and pushing,
  rather than podia

BrittleStar Movement
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• Feeding types
• Carnivore
• Scavenger
• Suspension feeder
• Deposit feeder
• Gut is restricted to a blind sac in disk
• Stomach is not eversible
• Mouth surrounded by jaws
• No intestine, no digestive glands in arms
• No anus

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• Suspension feeders
• Cast mucus strings like spider webs between arms
• Tube feet pairs gather particles, compact them
  into a pellet, and transport it to the aboral
  part of the disk

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• Carnivores and suspension feeding basket stars
• Capture prey with muscular arms
• Can be very rapid
• Minute hooks secure prey in basket star
• Move to mouth and swallowed
• Note one species of brittle star would eat until
  its disk ruptured

Feeding
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• No papulae
• Through tube feet
• 10 Bursae

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• Gonads in Bursae
• Produce gametes
• Shed into water
• External fertilixation
• Brooding with direct development common

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• In non-brooding sexual development
• Ophiopluteus larvae
• Metamorphose while swimming

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• Sea urchins, sand dollars, sea biscuits
• 950 species
• Graze on rock
• Name means hedgehog
• No arms
• Ambulacra and oral surface expanded to most of
  body
• Types
• Regular most urchins
• Irregular sand dollars, seasbiscuits

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• Ossicles fused into a test
• Body has 10 radial sections
• 5 sections have tube feet -ambulacral areas
• Paired pores for tubefeet - unique
• 5 sections w/o tubefeet (interambulacral areas)

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Adapted for soft and hard substrate Use Tube feet
and Spines Spines Two kinds Long primary Short
secondary
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Spines

• Have ball and socket to allow motion
• 2 sheaths of fibers surrounding ball
• Muscular
• Collagen locks spine
• Some deep sea urchins have poisonous spines

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• Pedicillaria
• Long moveable stalk
• Jaws
• Some are poisonous
• Can be used to hold bits of shell

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• Mostly grazers
• Rasp food with teeth of Aristotles lantern

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• Aristotles lantern
• Jaws
• Pharynx
• Can be protruded through periostomial membrane
• Used for boring into rock for some species

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• Esophagus
• Stomach
• Has special groove or tube to get rid of water
  (Siphon)
• Intestine
• Anus

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• Essentially the same as the Asteroidea

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• Peristomial gills
• Coelomic fluid pumped to gills via Aristotles
  lantern
• Tube feet

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• Anus
• Nitrogenous waste
• Gills
• Tube feet
• Axial gland (heart-kidney)

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• Similar to Ophiuroidea
• Circumoral nerve ring
• Five pair of radial nerves
• Sensory
• Tube feet - multi
• Pedicillaria - multi
• Spines - multi
• Light receptors
• Negatively phototactic
• Statocysts

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• Sexual
• Gonochoric
• 5 gonads, suspended on interambulacra
• External fertilization
• Some brood
• Echinopluteus larvae
• Sand dollar larvae settel and metamorphose in
  response to chemical cue from adults
• Sand dollars can limit their own density

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• Sea cucumbers
• 1200 species
• Greatest diversity in habitats
• Burrow in sediment
• Crawl on sediment
• Attach to hard substrate
• Climb on algae
• pelagic
• No arms
• Ambulacral run longitudinally and are enclosed

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• Body elongated
• Ambulacra on ventral side more developed
• 3 on ventral
• 2 on dorsal
• Test greatly reduced small remnants

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• Peristalsis
• Creep on tube feet
• Use buccal podia
• Some sessile
• Swimmers

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• Similar to Ophiuroidea and Echinoidea

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• Buccal podia
• Tube feet
• Respiratory trees (main)
• Water pumped by cloaca

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Intake

• Cloaca dilates

• Water moves in

• Cloaca contracts

• Water forced into respiratory trees

Exhaust

• respiratory trees contract

• Water moves out

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• Some eject Cuverian tubules from anus
• Sticky
• Toxic (holothurin)

• Evisceration

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• Anus
• Nitrogenous waste
• Probably through respiratory tree and body wall

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• Sexual
• 1 gonad
• External fertilization
• Some brood
• Catch fertilized eggs with buccal podia
• Some viviparous
• Young rupture mothers body wall to hatch
• Planktonic larva

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• Sea lilies and feather stars
• 700 species