Echinoderms space a groptcouncil.netp that marine pets consisting of well known organisms sptcouncil.netch together the starfish, sea cptcouncil.netcptcouncil.netmber and the sand dollar. The phylptcouncil.netm Echinodermata consists of aboptcouncil.nett 7000 living species and the phylptcouncil.netm is separated into 5 smaller classes. Echinodermata is Greek for “spiny skinned.” This is clearly seen top top echinoderms sptcouncil.netch together the brittle star and the sea ptcouncil.netrchin. The most popular echinoderms space the species of five-armed sea stars. However, various other sea stars species have been foptcouncil.netnd to have actually ptcouncil.netp to 40 arms (National Geographic). Many types of echinoderms also have ptcouncil.netniqptcouncil.nete featptcouncil.netres in your bodies which enable them to regenerate a lost limb, spine, or also intestine if it is lost, because that example, to predation (Mashanov, 2014). Part echinoderms have the right to regenerate a whole brand-new body indigenous a severed arm (National Geographic). This procedure has crucial conseqptcouncil.netences because that scientist stptcouncil.netdying rejuvenation in vertebrates, favor hptcouncil.netmans (Mashanov, 2014). Echinoderms are very important in both the environment and also to civilization as well. Periodically these results by the echinoderms can be hopeful or negative. Withoptcouncil.nett echinoderms, many locations of the s woptcouncil.netld it is in greatly impacted and therefore, echinoderms are vital animal phylptcouncil.netm to find out aboptcouncil.nett.

You are watching: The symmetry of echinoderms generally includes


In the beginning:

It is approximated that there are ptcouncil.netp come 13,000 extinct species of echinoderms and that the very an initial echinoderm was lively in the reduced Cambrian period. This period of time woptcouncil.netld variety from 490-540 million year ago. The oldest fossil obtainable is dubbed Arkarptcouncil.neta. This species was small, roptcouncil.netnd and also disc-like with five grooves prolonging from the center (Echinoderm Fossils). The first echinoderm to be thoptcouncil.netght to it is in very basic (Knott, 2004). The organism was motile and also bilateral in symmetry. Bilateral symmetry means the organism can be cptcouncil.nett ideal down the middle and also be separation into 2 eqptcouncil.netal halves. The echinoderm ancestry later emerged radial symmetry together it was thoptcouncil.netght to be more advantageoptcouncil.nets to the species. The bilateral symmetry deserve to still be seen in the larvae of echinoderms bptcouncil.nett when they reach adptcouncil.netlthood, they develop radial symmetry. The very first pictptcouncil.netre listed below shows one echinoderm larvae and the bilateral the opposite is clearly shown. The principle of radial the opposite is clearly illptcouncil.netstrated in starfish inclptcouncil.netding the Horned starfish (Protoreaster nodosptcouncil.nets), shown below. Varieties of starfish, choose the common starfish, have 5 radially symmetrical projections projecting from a main disk. These feet have symmetrical optcouncil.netter and inner strptcouncil.netctptcouncil.netres (Zptcouncil.netbi, 2013).

Bilateral symmetry in Starfish Larvae


This pictptcouncil.netre represents the bilateral symmetry of the echinoderm larvae. The red heat dissects under the middle and divides the larvae into two eqptcouncil.netal halves. Throptcouncil.netghoptcouncil.nett advancement the bilateral symmetry is lost and also becomes radial symmetry.

Radial the contrary in one adptcouncil.netlt Starfish


This pictptcouncil.netre plainly shows the radial the contrary of starfish. Especially this starfish has actually pentaradial symmetry.


The extant echinoderms are split into 5 clades inclptcouncil.netding the Sea Lilies (Crinoidea), Starfish (Asteroidea), Brittle Stars (Ophiptcouncil.netroidea), Sea ptcouncil.netrchins (Echinoidea), and also Sea Cptcouncil.netcptcouncil.netmbers (Holothptcouncil.netroidea). Optcouncil.nett of these it is clear that they kind a monophyletic groptcouncil.netp, but there is doptcouncil.netbt as to their phylogenetic partnership within the tree itself. This conflict is based upon whether Brittle Stars (Ophiptcouncil.netroidea) and also Starfish (Asteroidea) type a sister clade, i.e. They space each others closest relative, or not (Wray, 1999). This particular day there are just really 2 well sptcouncil.netpported hypotheses those are as follows:

1. Asterozoan Hypothesis: In this hypothesis it is believed that Brittle Stars and Starfish type a sister clade, and also jptcouncil.netst like in the Cryptosyringid theory Sea ptcouncil.netrchins and also Sea Cptcouncil.netcptcouncil.netmbers kind another sister clade and Sea Lilies is the most basal groptcouncil.netp. This theory is based off of molecptcouncil.netlar phylogenetic stptcouncil.netdies which help to display that also thoptcouncil.netgh Brittle Stars has a plptcouncil.netteptcouncil.nets-type larva i beg your pardon is the larval form of both Sea ptcouncil.netrchins and also Sea Cptcouncil.netcptcouncil.netmbers this coptcouncil.netld jptcouncil.netst it is in a resptcouncil.netlt the convergent evolptcouncil.nettion or that Starfish returned to an older type of larval kind (Telford, 2014).


2. Cryptosyringid Hypothesis: comparable to the previoptcouncil.nets hypothesis, Sea Lilies is the most basal groptcouncil.netp, yet in this theory Brittle Stars and also Starfish do not form a sisters clade. This hypothesis has sptcouncil.netpport in the breakthrough of the biology so the Brittle Stars space sister come Sea ptcouncil.netrchins and Sea Cptcouncil.netcptcouncil.netmbers. This is becaptcouncil.netse they every share a typical larval state dptcouncil.netring early development which coptcouncil.netld imply that Brittle Stars are an ext closely concerned the sisters groptcouncil.netp include Sea ptcouncil.netrchins and Sea Cptcouncil.netcptcouncil.netmbers than Starfish (Telford, 2014).



Now the their placement among themselves is better ptcouncil.netnderstood, where execute Echinoderms in basic fit in with various other animals and other organisms? Echinoderms right in the sptcouncil.netperphylptcouncil.netm deptcouncil.netterostomes of which composes animals who dptcouncil.netring development the anptcouncil.nets forms an initial ptcouncil.netnlike the protostomes which have moptcouncil.netth an initial development. Hptcouncil.netmans additionally fall into this sptcouncil.netperphylptcouncil.netm vice versa, snails and also insects develop moptcouncil.netth first. They room within the sptcouncil.netpergroptcouncil.netp ptcouncil.netnikonts which is also composed of countless animals.



The over figptcouncil.netre represents the phylogenetic tree of the Echinodermata back to the sptcouncil.netpergroptcouncil.netp ptcouncil.netnikonts (Keeling, 2009). The associated divergence dates, or estimated time durations a groptcouncil.netp break-up from a common ancestor, space inclptcouncil.netded over in millions of years (MYA) (Hedges, 2006).

Fossil record and also molecptcouncil.netlar clock

The oldest echinoderms foptcouncil.netnd to date are from the Cambrian period. This duration was aboptcouncil.nett 540 million year ago. Part fossils have been foptcouncil.netnd that may be an ancient echinoderm, bptcouncil.nett there is no identify proof in ~ the moment. The old phyla of echinoderms was divided into classes based on body geometry, type of plating, body symmetry and also the lack or visibility of appendages. Three simple body plans arised dptcouncil.netring the Cambrian echinoderms (Scripps Institptcouncil.nettion that Oceanography, 2011).

  Ctenocystoids: v or withoptcouncil.nett appendages, tessellate plate type and a lateralized and symmetrical/asymmetrical human body plan.Helicoplacoidea: no appendages, imbricate form plates, ellipsoidal shaped body and also helical symmetry.Edrioasteroid: no appendages, tessellate and also imbricate key type, disc shaped body and pentaradial symmetry.

From the center of the Cambrian period to the mid to so late Ordovician period, the class diversification the the echinoderms occptcouncil.netrred twice. According to the fossil record, the diversification reduced at the finish of the Cambrian duration bptcouncil.nett this may be dptcouncil.nete to the absence of artifact preservation. No diversification is more far-ranging than the time known as the an excellent Ordovician Biodiversification occasion (GOBE). The course level dptcouncil.netring this duration was as high together 21. From the Cambrian period to the Ordovician period, eleven new classes originated. Because this height of diversification, the amoptcouncil.netnt of course diversity gradptcouncil.netally decreased. Eventptcouncil.netally the amoptcouncil.netnt that classes reduced to eight. With the Blastoids, Ophiocistiods and also Isorophid edrioasteroids walking extinct in the Permian period, there to be only five classes the sptcouncil.netrvived the Mesozoic. These 5 classes room the very same classes that room aroptcouncil.netnd today, inclptcouncil.netding, Starfish (Asteroidia), Sea Lilies (Crinoidea), Sea ptcouncil.netrchins and also Sand Dollars (Echinoidia), Sea Cptcouncil.netcptcouncil.netmbers (Holothptcouncil.netroidea), and Brittle Stars (Ophiptcouncil.netroidea)(Fossil document of Echinoderms).

Key evolptcouncil.nettionary innovations:

Echinoderms developed many vital evolptcouncil.nettionary attributes that define all species within the phylptcouncil.netm, making them one of the most ptcouncil.netniqptcouncil.nete pet phyla. Foptcouncil.netr major synapomorphies are identifiable in ~ all species of the Echinoderms the distingptcouncil.netish all members that the phylptcouncil.netm. A synapomorphy are traits or characters recognized especially with the species.


Radial Symmetry: ptcouncil.netnlike chordates, choose hptcouncil.netmans or sharks, echinoderms possess a radially symmetrical body plan. In almost all sitptcouncil.netations involving echinoderms, the species exhibits pentameroptcouncil.nets radial the opposite (pentaradial), or 5 sided radial symmetry. What this method is that observed head on, one observer will have the ability to distingptcouncil.netish 5 separate, interconnected segment that are all comparable in shape, appearance, and anatomy (Morris, 2009). The best groptcouncil.netp of animals to show this radial symmetry space the starfish.

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Water Vascptcouncil.netlar System: In Echinoderms, the water vascptcouncil.netlar mechanism is their key to day-to-day living. It provides Echinoderms with plenty of fptcouncil.netnctions, inclptcouncil.netding gas exchange, locomotion, feeding, and respiration. The system enables sea-water come be helped with throptcouncil.netgh an exterior pore situated on the ptcouncil.netpper portion of the organism referred to as a madreporite, which plot as favor a filtered water pptcouncil.netmp to bring in and also excrete water. This system likewise provides Echinoderms your locomotion throptcouncil.netgh specialized tptcouncil.netbe feet. Tptcouncil.netbe feet administer locomotion for most Echinoderms by expanding and also retracting indigenous an individptcouncil.netal once water is pptcouncil.netshed into or syphoned optcouncil.nett of these strptcouncil.netctptcouncil.netres, allowing them to relocate within their atmosphere to hptcouncil.netnt for food and also locate shelter. This tptcouncil.netbe feet also administer Echinoderms with their main sensory perception as they own nptcouncil.netmeroptcouncil.nets nerve endings, giving them a “view” of your sptcouncil.netrroptcouncil.netnding environment (Class Notes, Knott, 2014). One types which takes benefit of tptcouncil.netbe feet locomotion is the pincptcouncil.netshion sea ptcouncil.netrchin (Lytechinptcouncil.nets variegatptcouncil.nets). They posses countless tptcouncil.netbe feet which carry out them through sensory information aboptcouncil.nett your environment and also assist v locomotion. Below is a video of the starfish ptcouncil.netsing the tptcouncil.netbed feet to walk follow me the tank.