| Eleutherozoa | ||||||
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 Pisaster ochraceaus
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Eleutherozoa is a subphylum of echinoderms. Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) Starfish (also called sea stars) are any Echinoderms belonging to the class Asteroidea. Sea urchins are small globular spiny sea cat animals composing most of class Echinoidea. The sea cucumber (also known as trepang, bêche-de-mer, or ambiguously Sea slug) is an Echinoderm of the class Holothuroidea Incertae sedis ( Latin for "of uncertain placement" abbreviated "inc Brittle stars, or ophiurids, are Echinoderms closely related to Sea stars. In life a subphylum is a Taxonomic rank intermediate between phylum and superclass. Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) They are mobile animals with the mouth diceted towards the substrate. They usually have a madreporite, tube feet, and moveable spines of some sort, and some have Tiedemann's bodies on the ring canal. The madreporite is an opening used to filter water into the Water vascular system of Echinoderms It is visible as a small red or yellow button-like structure looking Tube feet are the many small tubular projections found most famously on the ventral face of a Starfish 's arms but are characteristic of the Water vascular system All living echinoderms except Crinoidea belong here. Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the Echinoderms (phylum Echinodermata
Systematics
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. Brittle stars, or ophiurids, are Echinoderms closely related to Sea stars.
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 term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism Cladistics is the hierarchical classification of Species based on evolutionary ancestry Starfish (also called sea stars) are any Echinoderms belonging to the class Asteroidea. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor 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. eVolution is the third Album by eLDee, it was due to be released in 2008 A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor 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. In Phylogenetics, a basal Clade is the earliest clade to branch in a larger clade it appears at the base of a cladogram [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]
| ELEUTHEROZOA |
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Footnotes
- ^ Wray (1999)
- ^ Smith, A. Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the Echinoderms (phylum Echinodermata Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but The sea cucumber (also known as trepang, bêche-de-mer, or ambiguously Sea slug) is an Echinoderm of the class Holothuroidea Sea urchins are small globular spiny sea cat animals composing most of class Echinoidea. (2007). "Echinoderms: Attachment, torsion and the origins of a radical new body plan" in Palaeontological Association Annual Meeting. Budd, G. E. ; Streng, M. ; Daley, A. C. ; Willman, S. Programme with Abstracts 51.
- ^ Smith, A. B. (2005). "The pre-radial history of echinoderms". Geological Journal 40: 255–280. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
References
- Wray, Gregory A. (1999): Tree of Life Web Project: Echinodermata: Spiny-skinned animals: sea urchins, starfish, and their allies. The Tree of Life Web Project is an ongoing Internet project providing information about the diversity and Phylogeny of Life on Earth Version of 1999-DEC-14. Retrieved 2008-FEB-02.
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