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Phylum Echinodermata Definition, Classification, Characteristics, Examples

Echinoderms are coelomates that have pentamerous radial structure, but without distinct brain or head. They possess an endoskeleton composed of calcareous pieces...

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This article writter by MN Editors on November 20, 2021

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Phylum Echinodermata Definition, Classification, Characteristics, Examples
Phylum Echinodermata Definition, Classification, Characteristics, Examples

Phylum Echinodermata Definition

Echinoderms are coelomates that have pentamerous radial structure, but without distinct brain or head. They possess an endoskeleton composed of calcareous pieces or plates, and a distinct water vascular system that is coelomic in origin that has tube-feet, or podia protruding from the body.

Characteristics of Phylum Echinodermata 

  • They are marine only they are the largest of widespread and widespread marine mammals.
  • They are found in all oceans from intertidal zones up to the deepest depths.
  • They are a part of an organ-grade system for body organization.
  • Symmetry is usually radial and nearly always pentamerous.
  • The body is triloblastic and coelomate with distinct oral as well as aboral surfaces. It is not characterized by a any distinct head or segmentation.
  • They range from moderate to substantial dimensions, but they are not microscopic.
  • Body shape : globular or star-like, spherical discoidal or extended.
  • The body’s surface is not always smooth, and is usually is covered by five symmetrically radiating grooves known as ambulacra that have five inter-ambulacra with 5 different radii.
  • The body’s wall is comprised of an epidermis on the outside, a middle dermis and an inner layer of the peritoneum.
  • Endoskeleton is made up of tightly aligned plates, forming an outer shell, commonly referred to as theca or test. It could also comprise separate, tiny Ossicles.
  • The coelom has a large area that is lined by the peritoneum. It’s occupied by the reproductive and digestive system. It is formed from an embryonic archenteron i.e. enterocoel.
  • Coelom, a type of enterocoelous, is the perivascular cavity of the water the vascular system. Coelom fluid is composed of coelomocytes.
  • The water-vascular system is that is coelomic in origin, including tube feet or podia for movement and often with madreporite.
  • The alimentary canal typically in the form of a tube with a curly arc that runs from the mouth at the surface of the mouth to the anus located on the oral or aboral surface.
  • Haemal, blood or vascular lacunar system that is enclosed by coelomic peripheral channels.
  • Respiratory organs comprise branchiae tubes, respiratory tree and bursae.
  • A nervous system that does not have a brain, but with a ring around the circumoral area and the radial nerve.
  • Its excretory system seems not working.
  • Sensory organs that are not developed comprise chemoreceptors, tactile organs terminal tentacles, photoreceptors and statocysts.
  • The sexes are typically dioecious, with a some exceptions.
  • Gonads that are large, one or more fertilization external; only a few echinoderms have viviparous.
  • The development is intermediate, with typical larvae that undergo metamorphosis into radially symmetrical adults.
  • Regeneration of damaged parts is a unique feature.

Phylum Echinodermata Classification

The classification is based on Hyman, L.H. (1995). Only orders and living classes have been mentioned.

Subphylum 1. Pelmatozoa (Gr., pelmatos=stalk+ zoon=animals)

  • Most echinoderms are extinct.
  • Sedentary Echinoderms.
  • Body is attached to the surface of the aboral by the aboral stalk.
  • The mouth and the anal aperture are located on the front of the mouth, with the face facing towards the sky.
  • Viscera is enclosed within the test of calcareous.
  • No suckers.
  • Tube feet, also known as podia, are mostly used for food-catching.
  • The central nervous system is aboral.
  • There is only one living class.

Class 1. Crinoidea (Gr., crinon=lily+ eidos= form)

  • Often referred to as Sea Lillies or feather stars.
  • Living and extinct forms.
  • Living members have no stalk and are free to move, but they have an their extinct form is anchored by stalks.
  • The body is comprised from an aboral cup calyx, the oral cover or roof, also known as the tegmen and is extremely pentamerous within structures.
  • The mouth and the anus on the surface of the mouth.
  • Arms moveable and simple, mainly branches, usually 5 or 10 numbers without or with pinnules.
  • Tube feet with no suckers; without spine, madreporite and pedicellariae.
  • Ambulacral grooves can be seen open and extend down arms and pinnules until their ends.
  • The genders are distinct.
  • Larva doliolaria.

Order 1. Articulata

  • Living and extinct crinoids.
  • Free and non-sessile swimming.
  • Calyx pentamerous and flexible. It incorporates the lower arm and ossicles.
  • Tegmen leathery is made up of tiny plates or calcareous particles.
  • The ambulacral grooves and mouth are exposed.
  • Some examples: Antedon (sea lily), Rhizocrinus, Metacrinus.

Subphylum 2. Eleutherozoa (Gr., eleutheros=free+ zoon= animals)

  • Free-living echinoderms.
  • The stalk or stem are not present typically living forms that are free of charge.
  • Pentamerous body tightening.
  • The surface of the mouth that is abrasive is downwards or lies on one side.
  • Anus typically is located on the aboral area.
  • Ambulacral grooves are generally not used intended for gathering food.
  • Tube feet that have suckers are mostly locomotory organs.
  • The primary nervous system of the oral.

Class 1. Holothuroidea (Gr., holothurion=water polyp+ eidos=form)

  • Also known as sea cucumbers.
  • Body bilaterally symmetrical, typically extended in the oral-aboral axis, with a mouth close to the one end, and an auricle close to the other end.
  • Coarse body surface.
  • Endoskeleton reduced down to microscopic spikes or plates that are embedded into the body’s wall.
  • Anterior mouth, enclosed by tentacles connected by the water-vascular system.
  • Ambulacral grooves hidden.
  • Tube feet, also known as Podia, are typically present, as well as motorized.
  • The canal for the alimentary tract is lengthy, wrapped in.
  • Cloaca is usually paired with trees to help the purpose of respiration.
  • The sexes are separated and go through one or two tufts, or tubules.

Order 1. Aspidochirota

  • Tube feet, also known as Podia, can be found in a variety of forms, often forming the sole of a properly-developed one.
  • Tentacles are leaf-like or peltate.
  • The mouth is enclosed by 10-30 mainly 20 oral tentacles that are peltate or branching.
  • The muscles that retract the pharynx are missing.
  • An established respiratory tree is in place.
  • Examples: Holothuria, Stichopus, Mesothuria.

Order 2. Elasipoda

  • Many podias or tube feet.
  • Tentacles leaf-like.
  • Tube feet interconnected to make fins.
  • The mouth is typically ventral and is surrounded by 10-20 peltates or branched tentacles.
  • Retractors for oral cavity are absent.
  • Aucune tree respirative.
  • Deep-sea dwellers.
  • Examples: Deima, Benthodytes.

Order 3. Dendrochirota

  • Tube feet or Podia are numerous on the sole or even the entire surface.
  • Tentacles that are not branched in a regular fashion.
  • Oral retractors present.
  • Respiratory trees are in the area.
  • Examples: Thyone, Cucumaria, Phyllophorus.

Order 4. Molpadonia

  • Tube feet or Podia are not present except as anal papillae.
  • 15 finger-shaped or digitate tentacles.
  • Posterior tail tail-like.
  • Oral retractors do not exist.
  • Respiratory trees are in the area.
  • Examples: Molpadia, paracaudina.

Order 5. Apoda

  • The worm-like Sea Cucumbers.
  • No tubing feet, and no respiratory tree.
  • Body vermiform with an even or smooth surface.
  • Tendons for the oral cavity are 10-20 simple digitate, pinnate or digitate.
  • Pharyngeal retractors are found in various varieties.
  • The water-vascular system has been significantly diminished.
  • Examples: Synapta, Chiridoata.

Class 2. Echinoidea (Gr., echinos=hedgehog+eidos=form)

  • Also known as Sea Urchins or Sand Dollars.
  • It is round disc-like, oval or heart-shaped.
  • The body is encased in an endoskeletal shell, or test composed of calcareous plates with moveable spines.
  • Outer calcareous plates are divided into five ambulacral alternating areas and 5 inter-ambulacral regions.
  • Podia or tube feet emerge out of the plates that ambulacrals sit on and serve as functionally locomotor.
  • The mouth is situated centrally on the oral surface , and is surrounded by a membranous oristome.
  • The Chewing Apparatus of the lantern Aristotle that has teeth.
  • Ambulacral grooves surrounded by Ossicles; tube feet with suckers.
  • The anus is situated at the aboral pole. It is also it is surrounded by a membranous.
  • Pedicellariae are stalked , and have three jaws.
  • Sexuality is a separate issue. Gonads are usually less than five.
  • The development is characterized by the free-swimming larva of echinopluteus.

Subclass 1. Bothriocidaroida

  • Each inter-ambulacral has only one plate.
  • There is no typical lantern.
  • Radial madreporite.
  • Include one extinct Ordovician Genus.
  • Example: Bothriocidaris.

Subclass 2. Regularia

  • Body globular, mainly circular , but sometimes oval.
  • Symmetry pentamerous that has 2 rows inter-ambulacral plates on existing members.
  • Mouth central on the surface of the mouth and is surrounding by peristome.
  • The Aristotle lantern is well-developed.
  • The anus is located centrally on the aboral pole and is surrounded by the periproct.
  • Madreporite is an ambulacral.

Order 1.  Lepidocentroida

  • Test the flexibility using plates that overlap.
  • Ambulacral plates can extend to the lip of the mouth.
  • Inter-ambulacral plates that are more than two rows in the extinct forms.
  • Example: Palaeodiscus.

Order 2. Cidaroidea

  • Test the globularity and rigidity of the test.
  • Two rows of ambulacral plates that are long and narrow as well as two inter-ambulacral plate rows.
  • Gills and sphaeridia do not exist.
  • Plates for inter-ambulacral and ambulacral continue until the mouth’s lips.
  • Anus is aboral, and central.
  • 5 organs from the Bushy Stewart’s are attached onto the lightbulb.
  • Examples: Cidaris, Notocidaris.

Order 3. Aulodonta

  • Test both symmetrical and global.
  • Test consisting of two rows of an inter-ambulacral and plates for ambulacral.
  • Ambulacral and inter-ambulacral plates extend up to the edge of the peristome.
  • Gills and sphaeridia do not exist.
  • Teeth from Aristotle’s lantern free of the keel.
  • Examples: Diadema, Astropyga.

Order 4. Camarodonta

  • The test is extremely rigid and is rarely oval.
  • The epiphyses of the lantern are larger and are arranged to meet above pyramids.
  • Teeth are gekeled.
  • All four types of pedicellariae can be found.
  • Examples: Echinus, Strongylocentrotus.

Subclass 3. Irregularia

  • The body is oval or circular. or circular, and flattened in the oral-aboral area.
  • Symmetry can be bilateral.
  • Orally displaced or centrally over the surface of the mouth.
  • The anus is located forward, generally marginal to the surface of the mouth or the aboral and is outside the apical plates.
  • Tube-feets or Podia are generally are not locomotor.

Order 1. Clypeastroida

  • Test is flattened using an oval or round shape and covered with tiny spines.
  • Apical and oral systems are generally central and orally in the position.
  • Aboral ambulacral.
  • The lantern of Aristotle in the present.
  • Gills are not present.
  • Bottom dwellers.
  • Examples: Sand dollars: Clypeaster, Echinarachinus, Echinocyamus.

Order 2. Spatangoida

  • Check out the oval, or heart shape shape with anus and an excentric mouth.
  • 4 aboral ambulacral pataloid areas.
  • No lantern.
  • Gills are absent.
  • Burrowing.
  • Examples: Heart urchins; Spatangus, Echinocardium, Lovenia.

Class 3. Asteroidea (Gr., aster=star+ eidos= form)

  • Often, they are referred to as starfishes or stars.
  • The body is flat or pentagonal. It can also be star-shaped.
  • Surfaces for the aboral and oral are distinct, with the oral surface inclined downwards, and the aboral surface directed upwards.
  • Arms 5 or more , and not sharply separated from the disc in the center.
  • The mouth is situated centrally on the oral surface, and is and is surrounded by a membranous oristome.
  • The anus is tiny and obscurely located in a more or less irregular position on the surface of the aboral.
  • Tube feet that are placed orally grooves for ambulacral insertion; with suckers.
  • Ambulacra are limited to the oral area that extends from the peristome’s top to the arms’ ends.
  • Endoskeleton is flexible, and is made of ossicles that are separate.
  • Pedicellariae are small, movable spine-like always present.
  • Papulae are the most common cause of respiratory irritation.
  • The sexes are separated, and gonads are radiatally placed.
  • The development also includes bipinnaria and branchiolaria larvae.

Order 1. Phanerozonia

  • The body is covered with marginal plates, and, more often, papulae on the aboral surface.
  • Arms come with 2 rows of distinctive marginal plates.
  • Oral plates are infra-marginal , and oral plates can be supra-marginal.
  • Pedicellariae alveolar or sessile type, but not crossed.
  • Podia or tube-feets are placed in two rows, without suckers.
  • Its mouth frames are formed and is adambulacral in type.
  • Most burrowers are soft bottomed.
  • Examples: Luidia, Astropecten, Archaster, Pentaceros.

Order 2. Spinulosa

  • Arms are usually not marked by plate borders.
  • The aboral skeleton is imbricated , or reticulated by one or more spines.
  • Pedicellariae are rare.
  • Tube feet are divided into two rows, with suckers.
  • It is an adambulacral form.
  • Aboral surface with spines that are low.
  • Ampullae, bifurcated or single.
  • Examples: Aesterina, Echinaster, Hymenaster, Solaster.

Order 3. Forcipulata

  • No prominent plates on the margins.
  • Aboral bone skeletons are recticulate, with prominent spines.
  • Pedicellariae are a pedunculate species with a basal part.
  • Podia feet or tube feet are set in four rows and are paired with suckers.
  • Papulae can be found on both surfaces.
  • The frame of the mouth is of the an ambulacral form.
  • Examples: Brisingaster, Heliaster, Zoraster, Asterias.

Class 4. Ophiuroidea (Gr., ophis=serpent+ oura=tail+ eidos= form)

  • They are also known as brittle-stars and allies.
  • The body’s shape is flattened using an elongated or pentamerous central disc.
  • Aboral and oral areas are distinguished.
  • The body is star-like, with arms clearly separated away from central disc.
  • Pedicellariae absent.
  • Ambulacral grooves are not present or covered by Ossicles.
  • There is no anus and there is no the intestine.
  • Stomach sac-like.
  • Tube feet that do not have suckers.
  • The madreporite is located on the surface of the mouth.
  • Genders are different, and pentamerous.
  • Bursa typically 10.
  • The development also included a free-swimming larva.

Order 1. Ophiurae

  • Serpent and Brittle stars.
  • Arms are simple, typically five in number, and move mostly across the transverse plane.
  • Ossicles in the arms are articulated by pits or projections.
  • Arms and discs are typically covered by distinct shields or scales.
  • Spines on arms move laterally, and they are pointed outwards towards the tips of the arm, but not downwards.
  • Single madreporite.
  • Examples: Ophioderma Ophioscolex, Ophiothrix, Ophiolepie.

Order 2. Euryalae

  • Arms that are simple or branched, large and flexible. They’re capable of wrapping around objects and rolling upwards on the horizontal plane.
  • The arms’ ossicles are connected in streptospondylus way.
  • Arms and discs covered with soft skin.
  • Spines are often directed downwards making hooks or spiny club.
  • One madreporite per inter-radius.
  • Examples: Asteronyx, Gorgonocephalus (basket stars).

Importance of Phylum Echinodermata

As food and medicine

  • In 2010, 373,000 tonnes of echinoderms were gathered, mostly to be consumed as well as for use in traditional Chinese medicines. They were mostly sea cucumbers (158,000 tonnes) and sea urchins (73,000 tonnes).
  • Sea cucumbers are regarded as to be a speciality in some countries in south east Asia and, as so, they’re at risk of becoming over-harvested. The most popular species are those that roll in pineapple Thelenota thelenota ananas (susuhan) along with The purple Holothuria edulis. The two species, along with others, are often referred to as beche de the mer or trepang from China as well as Indonesia.
  • The sea cucumbers are simmered for about 20 minutes before being dried naturally and later on a stove, giving the sea cucumbers a smoky flavor.
  • The Chinese use them as a base for their stews. China they are often used to make gelatinous stews and soups.
  • Female and male the gonads from sea urchins are popularly consumed within Japan, Peru, Spain and France. The flavor is described as melting and soft like a mix of fruits and seafood.
  • Presently there are some breeding trials for sea urchins to counteract for the excessive use of this resource have been conducted.

In research

  • Sea urchins are utilized in research, specifically as models for the field of developmental biology and ecotoxicology. Strongylocentrotus purpuratus as well as Arbacia punctulata are employed to study embryology. research.
  • The size of the eggs and the transparent eggs allow the study of sperm cells involved in the process of fertilizing the eggs.
  • The potential for regeneration of the arm in Brittle stars is being investigated to understand and treating neurodegenerative disorders in humans.

Other uses

  • The calcareous shells or tests of echinoderms are utilized for lime production by farmers in regions where limestone is scarce and some are also used to make fish meal. The equivalent of 4000 tonnes of animals are utilized every year to make this product. The trade is usually performed in conjunction with farmers of shellfish who believe that starfish pose a serious danger by eating their own stocks.
  • Other uses for the starfish that they are able to recover include the production from animal food, the composting process, and drying for the craft and arts trade
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