HISTORY

Phylum Echinodermata are defined as spiny skined animals (Greek word echinos = spiny; derma = skin). Beginning their life race from lower cambrian, they are successfully continuing their biological activities. Echinodenns are at the top of invertebrate and very close to the chordates. They are unique combination of advanced and primitive characters. The advanced characters

  • They ale deuterostomes,
  • Presence of mesodermal calcium carbonate endoskeleton (note other invertebrates have no endoskeleton),
  • Coelom enterocoelus,
  • Exclusively free-living marine.

DIAGNOSTIC CHARACTERS​ OF PHYLUM ECHINODERMATA

  • Spiny-skinned animals.
  • Triploblastic deuterostomes. 
  • Distinct head and segmentation absent. 
  • Body divided into oral and aboral surfaces.
  • Peculiar water vascular system for locomotion.
  • Exclusively marine. 
  • Non-microscopic.

CLASSIFICATION OF PHYLUM ECHINODERMATA

PHYLUM ECHINODERMATA

SUB-PHYLUM I PELMATOZOA

  1. Sedentary echinoderms.
  2. Oral surface oriented upwards and aboral surface with jointed cirri.

CLASS I CRINOIDEA

  •  Commonly called as sea lilies.
  • Body consists of a cup like calyx and cylindrical arms.
  • Tube feet, madreporite and pedicellaria absent.
    Example :- Antedon.
ANTEDON OR FEATHER STAR
ANTEDON OR FEATHER STAR

SUB-PHYLUM II ELEUTHEROZOA

  1. Free-living echinodenns.
  2. Oral surface directed downwards.

CLASS II ASTEROIDEA

  • Commonly called as star fishes.
  • Body star shaped central disc and arms not sharply demarcated

Order 1 Phanaerozonia

    1. Marginal plates distinct in 2 rows.
    2. Pedicellaria sessile.
      Example :- Pentaceros, Astropecten, Luidia, Anthena.

Order 2 Spinulosa

    1. Marginal plates indistinct.
    2. Pedicellariae pedunculate.
      Example :- Solaster, Asterina.

Order 3 Forcipulata

    1. Pedicellariaes traught or crossed.
    2. Tube feet in 4 rows.
      Example :- Pisaster, Asterias.
  1.  
ASTERIAS (STARFISH)​
ASTERIAS (STARFISH)​

CLASS III OPHIUROIDEA

  • Commonly called as brittle stars.
  • Central disk and arms sharply demarcated.

Order 1 Streptophiurae

    1.  Arms slender.
      Example :- Ophiomyxa

Order 2 Zygophiurae

    1. Arms simple with horizontal movement.
    2. Disk and arms covered by plates.
      Example :- Ophioderma, Ophiocoma, Ophiolepis, Ophiura,
      Ophiopholis.

Order 3 Cladophiurae

    1. Arms much elongated and rolled as basket.
    2. Called as basket star.
      Example :- Gorgonocephalus.
  1.  
OPHIOLEPIS
OPHIOLEPIS

CLASS IV ECHINOIDEA

  • Commonly called as sea urchins and sand dollars.
  •  Skeletal plates saturated forming a complete test.
  • Body disk shaped, egg-shaped or heart shaped.

Sub-class A. Bothriocidarida (Extinct)
Sub-class B. Regularia

    • Body globular, usually circular.
    • 5 petaloids radially symmetrical.
    • Locomotion by podia.

Order 1 Lepidocentroida

    1. Test flexible, imbricate or separate.
    2. Ambulacral plates continue on peristome.
      Example :- Phoromosa.

Order 2 Melonechinada (Extinct)

Order 3 Cidaroidea

    1. Anus aboral, central.
    2. Peristomial gills absent.
    3. Rigid globular test with two rows of long narrow ambulacral plates and 2 rows of interambulacral plates.
      Example :- Histocidaris, Apocidaris.

Order 4 Diadematoida

    1. Anus aboral central.
    2. Peristomial gills and Aristotles lantern present.
    3. Symmetrical globular test.
      Example :- Diadema, Echinus, Strongylocentrotus.

Sub-class C. Irregularia

    • Body flattened on oral aboral axis in oval manner but not exactly symmetrical.
    • Podia non-locomotor.

Order 1 Clypeastroida

    1. Commonly called as sand dollars.
    2. Test flattened or oval, lantern present and gills absent. Burry in sand.
      Example :- Clypeaster, Echinarachnius.

Order 2 Spatangodia

    1. Commonly called as heart urchins.
    2. Ambulacral plates petaloid.
      Example :- Echinocardium, Lovenia.
ECHINOCARDIUM
ECHINOCARDIUM

CLASS V HOTOTHUROIDEA

  • Commonly called as sea cucumbers.
  • Body elongated on oral-aboral axis with anterior mouth.
  • Skeleton of microscopic plates embedded in body wall.
  • Digestive system s-shaped Respiration by respiratory tree.

Order 1 Aspidochirota

    1. Tentacles branched anteriorly.
    2. Podia several.
    3. Respiratory tree present.
      Example :- Holothuria, Stichopus.

Order 2 Elasipoda

    1. Tentacles branched distally.
    2. Respiratory tree absent. Tube feet.
    3. Modified as fins.
      Example :- Pelagothuria.

Order 3 Dendrochirota

    1. Tentacles irregularly branched.
    2. Tube feet numerous.
    3. Respiratory tree present.
      Example :- Cucumaria, Thyone.

Order 4 Molpadonia

    1. Tentacles small hand shaped.
    2. Tube feet absent.
      Example :- Molpadia.

Order 5 Apoda or Synaptida

    1. Tentacles present. Body transparent.
    2. Tube feet, Respiratory tree absent.
      Example :- Synapta.
SEA CUCUMBER OR CUCUMARIA​ ​
SEA CUCUMBER OR CUCUMARIA​ ​
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