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Eleutherozoa

(Subphylum)

Overview

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Eleutherozoa is a subphylum of echinoderms. They are mobile animals with the mouth directed towards the substrate. They usually have a madreporite, tube feet, and moveable spines of some sort, and some have on the ring canal. All living echinoderms except Crinoidea belong here.

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There are 2 main competing hypotheses about the internal subdivision, both about equally well supported by both molecular and morphological data. They differ in their placement of the Ophiuroidea (brittle stars), and are named accordingly.

The "Cryptosyringida" hypothesis posits that the "sea-star" morphology is plesiomorphic for Eleutherozoa as a whole, and that starfish (Asteroidea) and brittle stars are not very closely related, the latter forming the clade Cryptosyringida together with the Echinozoa. The "Asterozoa " hypothesis on the other hand implies that the "sea-star" arms of starfish and brittle stars, as well as the rounded shape of Echinozoa, both evolved independently from an ancestor of unknown morphology, but that each "armed" and "rounded" lineages are strictly monophyletic. Too little is known of the basal eleutherozoans and echinoderms to be able to firmly decide for or against any of these hypotheses at present.[1]

The Asterozoa would have to be ranked as a superclass or treated as an unranked clade between the Cryptosyringida and the Eleutherozoa, depending on whether the "Asterozoa" or "Cryptosyringida" hypothesis turns eventually out to be correct.

Emerging research favours the following classification:[2][3]

Footnotes

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  1. ^ Wray (1999)
  2. ^ Smith, A. (2007). "Echinoderms: Attachment, torsion and the origins of a radical new body plan". In Budd, G.E.; Streng, M.; Daley, A.C.; Willman, S.. Programme with Abstracts. 51. Palaeontological Association Annual Meeting. Uppsala, Sweden. http://downloads.palass.org/annual_meeting/2007/palass2007_programme_abstracts.pdf. 
  3. ^ Smith, A.B. (2005). "The pre-radial history of echinoderms". Geological Journal 40 (3): 255?280. doi:10.1002/gj.1018. 
b>Eleutherozoa is a subphylum of echinoderms. They are mobile animals with the mouth directed towards the substrate. They usually have a madreporite, tube feet, and moveable spines of some sort, and some have on the ring canal. All living echinoderms except Crinoidea belong here.

[ Back to top ]

There are 2 main competing hypotheses about the internal subdivision, both about equally well supported by both molecular and morphological data. They differ in their placement of the Ophiuroidea (brittle stars), and are named accordingly.

The "Cryptosyringida" hypothesis posits that the "sea-star" morphology is plesiomorphic for Eleutheroz oa as a whole, and that starfish (Asteroidea) and brittle stars are not very closely related, the latter forming the clade Cryptosyringida together with the Echinozoa. The "Asterozoa" hypothesis on the other hand implies that the "sea-star" arms of starfish and brittle stars, as well as the rounded shape of Echinozoa, both evolved independently from an ancestor of unknown morphology, but that each "armed" and "rounded" lineages are strictly monophyletic. Too little is known of the basal eleutherozoans and echinoderms to be able to firmly decide for or against any of these hypotheses at present.[1]

The Asterozoa would have to be ranked as a superclass or treated as an unranked clade between the Cryptosyringida and the Eleutherozoa, depending on whether the "Asterozoa" or "Cryptosyringida" hypothesis turns eventually out to be correct.

Emerging research favours the following classification:[2][3]

Footnotes

[ Back to top ]
  1. ^ Wray (1999)
  2. ^ Smith, A. (2007). "Echinoderms: Attachment, torsion and the origins of a radical new body plan". In Budd, G.E.; Streng, M.; Daley, A.C.; Willman, S.. Programme with Abstracts. 51. Palaeontological Association Annual Meeting. Uppsala, Sweden. http://downloads.palass.org/annual_meeting/2007/palass2007_programme_abstracts.pdf. 
  3. ^ Smith, A.B. (2005). "The pre-radial history of echinoderms". Geological Journal 40 (3): 255?280. doi:10.1002/gj.1018. 

References

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Taxonomy

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The Subphylum Eleutherozoa is a member of the Phylum Echinodermata. Here is the complete "parentage" of Eleutherozoa:

The Subphylum Eleutherozoa is further organized into finer groupings including:

Classes

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Asteroidea

Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the class Asteroidea. However, common usage frequently finds "starfish" and "sea star" also applied to ophiuroids which are correctly referred to as "brittle stars" or "basket stars". [more]

Echinoidea

Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from 3 to 10 centimetres (1.2 to 3.9 in) across. Common colors include black and dull shades of green, olive, brown, purple, and red. They move slowly, feeding mostly on algae. Sea otters, wolf eels, triggerfish, and other predators feed on them. Their "roe" (actually the gonads) is a delicacy in many cuisines. [more]

Holothuroidea

Sea cucumbers are echinoderms from the class Holothuroidea. They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. There are a number of holothurian species and genera, many of which are targeted for human consumption. The harvested product is variously referred to as trepang, b?che-de-mer or balate. [more]

Ophiuroidea

[more]

At least 1,890 species and subspecies belong to the Class Ophiuroidea.

More info about the Class Ophiuroidea may be found here.

References

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Sources

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Last Revised: August 24, 2012
2012/08/24 17:24:59