14Echinodermata

▢ General Features:
❖ BodyStructure:
  1. Triploblastic
  2. Radially symmetrical (adult), often Pentamerous
  3. Larva is bilaterally symmetrical; sessile or creeping at bottom
  4. Radially arranged parts are called Antimeres
  5. Tube within tube body plan (Deuterostomes)
  6. Digestive tract complete (except in Brittle star)
  7. Enterocoelic coelomate
  8. Organ grade of organization
  9. Unsegmented body
▢ Habit: Gregarious, benthic(bottom dwellers) except the sea-cucumber which shows the pelagic habit that is the surface dweller.
▢ Habitat:
❖ Type: Exclusively marine
❖ Lifestyle:
  1. All are benthic (bottom dwellers), except few pelagic sea cucumbers
  2. Mostly free-living, except sea lilies
▢ Special Features:
❖ BodySurface:
  1. Spiny skinned
  2. Uncephalized (head absent)
  3. Body parts organized around oral-aboral axis
❖ Endoskeleton:
◉ Structure: Unique calcareous ossicles bearing protective spines
◉ Origin: Mesodermal
◉ Significance: Only phylum other than Chordata with true endoskeleton
❖ ExternalStructures:
  1. Spines – pointed for protection
  2. Pedicellariae – pincer-like, prevent setting of foreign particles
❖ SpecialOrgans: In Sea urchin, gut has a masticating organ called 'Aristotle’s Lantern'
❖ CoelomicSystems:
◉ Description: Complex coelom with derivatives: Water vascular system, Perivisceral coelom, Haemal system
◉ WaterVascularSystem:
◈ Pathway:
  1. Madreporite (Inlet canal)
  2. Stone canal (Madreporic canal)
  3. Ring canal (lined with Tiedmann's bodies for lymphocyte formation)
  4. Radial canal
  5. Lateral canal
  6. Tube feet (Ampulla, Podium, Sucker)
◈ Functions:
  1. Locomotion
  2. Respiration
  3. Food capturing
❖ DefenseAndRegeneration:
  1. Autotomy – breaking part to confuse enemy
  2. Evisceration – ejection of viscera
  3. Regeneration – by epimorphosis
❖ BodyWall: Contains muriform glands in epidermis for pigmentation
▢ Nervous System:
❖ Type: Diffuse and decentralized
❖ Components:
  1. Nerve net
  2. Nerve ring
  3. Radial nerves
❖ Note: No brain present
❖ SenseOrgans:
  1. Tactile tentacles
  2. Pigment eye-spots
  3. Statocysts (organs of balance/orientation with statoliths)
▢ Respiratory System:
❖ Organs:
    ◈ Animal: Starfish
    ◈ Organ: Dermal branchiae or Papulae
    ◈ Animal: Sea urchin
    ◈ Organ: Gills
    ◈ Animal: Sea cucumber
    ◈ Organ: Cloacal Respiratory Tree
    ◈ Animal: Brittle star
    ◈ Organ: Genital bursae
▢ Circulatory System:
❖ Type: Open
❖ Heart: Absent
❖ Blood: No respiratory pigment
▢ Excretory System: Absent
▢ Reproductive System:
❖ Type: Mostly dioecious
❖ Copulation: Absent
❖ Fertilization: External
❖ Eggs: Homolecithal (uniform yolk distribution)
❖ Development:
◉ Type: Indirect via free-swimming larvae
◉ Cleavage: Radial and indeterminate
◉ LarvalForms:
◈ Asteroidea (Starfish - Asteriasis):
  1. Bipinnaria
  2. Brachiolaria
  3. Dipleura
◈ Ophiuroidea (Brittle star - Ophiothrix):
  1. Ophiopluteus
◈ Echinoidea (Sea urchin - Echinus):
  1. Echinopluteus
◈ Holothuroidea (Sea cucumber - Cucumeria):
  1. Auricularia
◈ Crinoidea (Feather star - Antedon):
  1. Doliolaria
◉ Note: Dipleura is the common ancestral larval form of most deuterostomes
▢ Classification:
❖ Based on the shape/position of madreporite and characteristics of the digestive system:
S.N.
Asteroidea
Ophiuroidea
Echinoidea
Holothuroidea
Crinoidea
Body Form
  1. Star-like with 5 arms not demarcated from central axis
  2. • Starfish is benthonic (bottom dwelling), carnivorous animal.
  3. • Starfish is nocturnal and eats its prey.
  4. • Starfish is an enemy of Pearl oyster.
  5. • The stomach comes out of the body, feeds and digests food outside the body (i.e., extra oral digestion occurs in starfish).
  6. • Facts: The Sea Star (Starfish)
  1. Snake tail-like
  2. • Star-like with 5 arms demarcated from central axis.
  3. • Ambulacral grooves are absent in its living forms.
  4. • Facts: The Basket Star
  1. Spiny
  2. • Globular with no arms.
  3. • Skeleton bearing movable spines and three-jawed pedicellariae are present.
  4. • Facts: The Sea Urchin
  5. • It contains Sphaeridia.
  6. b. Echinocardium (Heart urchin)
  7. c. Clypeaster (Dollar star/Sand dollar)
  8. • Box-like calcareous test is found in Sand dollar.
  9. • Facts: The Sand Dollar
  1. Cucumber-like
  2. • No arms, no spines, no pedicellariae.
  3. • Madreporite is absent.
  4. • Feeds upon detritus and planktons.
  5. • Facts: The Sea Cucumber
  1. Lily flower-like
  2. • Arms bear pinnules.
  3. • Tube feet without suckers, no madreporite, spines and pedicellariae.
  4. • No madreporite
Madreporite location
Aboral
Oral
Aboral
Oral
No madreporite
Pedicellariae
Pedicellariae are present
Anus and pedicellariae are absent
Movable spines and three-jawed pedicellariae are present
No pedicellariae
No pedicellariae
Examples
  1. a. Asterias (Starfish)
  2. b. Astropecten (Starfish)
  3. c. Pentaceros (Sea pentagon)
  1. a. Ophiothrix (Brittle star)
  2. b. Gorgonocephalus (Basket star)
  1. a. Echinus (Sea urchin)
  2. b. Echinocardium (Heart urchin)
  3. c. Clypeaster (Dollar star/sand dollar)
  1. a. Cucumaria (Sea cucumber)
  1. a. Antedon (Feather-star / Sea lily)
  2. b. Holopus (Sea-lilies)
  3. c. Neometra (Feather star)
Q1.
Which of the following animal belongs to Echinodermata?
📅IOM 2003
Q2.
Locomotory organ in starfish is:
📅IOM 2002
Q3.
Well developed water vascular system is found in:
📅IOM 1997
Q4.
Which phylum is exclusively marine
📅MOE 2003
Q5.
Organisms attached to substratum generally possess
📅IE 2008
Q6.
In which of following classes of echinodermata bipinnaria larvae is found
📅IE 2004
Q7.
Which of the following is an echinodermata?
📅IOM 2014
Q8.
Echinodermata lives in