other organs and regeneration of echinoderm

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  • 7/25/2019 Other Organs and Regeneration of Echinoderm

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    Other organs

    Echinoderms possess a simple digestive system which varies according to the

    animal's diet. Starfish are mostly carnivorous and have a mouth, oesophagus, two-

    part stomach, intestine and rectum, with the anus located in the centre of the

    aboral body surface. In many species, the large cardiac stomach can be everted

    and digest food outside the body. In other species, whole food items such as

    molluscsmay be ingested.[2!"rittle stars have a blind gut with no intestine or

    anus. #hey have varying diets and e$pel food waste through their mouth.[2%!Sea

    urchins are herbivores and use their specialised mouthparts to gra&e, tear and

    chew algaeand sometimes other animal or vegetable material. #hey have an

    oesophagus, a large stomach and a rectum with the anus at the ape$ of the test. [2!

    Sea cucumbers are mostly detritivores, sorting through the sediment with their

    buccal tentacles which are modified tube feet. Sand and mud accompanies their

    food through their simple gut which has a long coiled intestine and a capacious

    cloaca.[2(!)rinoids are passive suspension feeders,catchingplan*tonwith their

    outstretched arms. "oluses of mucus-trapped food are passed to the mouth which

    is lin*ed to the anus by a loop consisting of a short oesophagus and longer

    intestine.[+!

    #he coelomic cavitiesof echinoderms are comple$. side from the water vascular

    system, echinoderms have a haemal coelomor haemal system, the /haemal/

    being a misnomer0, a perivisceral coelom, a gonadal coelom and often also aperihaemal coelom or perihaemal system0.[+1!uring development, echinoderm

    coelom is divided in metacoel, mesocoel and protocoel also called somatocoel,

    hydrocoel and a$ocoel, respectively0.[+2!#he water vascular system, haemal

    system and perihaemal system form the tubular coelomic system. [++!Echinoderms

    are an e$ception having both a coelomic circulatory system i.e., the water

    vascular system0 and a haemal circulatory system i.e., the haemal and perihaemal

    systems0.[+3!

    4aemal and perihaemal systems are derived from the coelom and form an open

    and reduced circulatory system. #his usually consists of a central ring and five

    radial vessels. #here is no true heartand the blood often lac*s any respiratorypigment. 5aseous e$change occurs via dermal branchae or papulae in starfish,

    genital bursae in brittle stars, peristominal gills in sea urchins and cloacal trees in

    sea cucumbers. E$change of gases also ta*es place through the tube feet.

    Echinoderms lac* speciali&ed e$cretory waste disposal0 organs and so

    nitrogenous waste, chiefly in the form of ammonia, diffuses out through the

    respiratory surfaces.[21!

    Echinoderms have a simple radial nervous systemthat consists of a modified

    nerve netconsisting of interconnecting neurons with no centralbrain, although

    some do possess ganglia. 6erves radiate from central rings around the mouth into

    each arm or along the body wall7 the branches of these nerves coordinate the

    https://en.wikipedia.org/wiki/Molluschttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert885-26https://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert891-27https://en.wikipedia.org/wiki/Algaehttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert904-28https://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert904-28https://en.wikipedia.org/wiki/Detritivorehttps://en.wikipedia.org/wiki/Cloacahttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert912-29https://en.wikipedia.org/wiki/Suspension_feederhttps://en.wikipedia.org/wiki/Suspension_feederhttps://en.wikipedia.org/wiki/Planktonhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert920-30https://en.wikipedia.org/wiki/Body_cavityhttps://en.wikipedia.org/wiki/Circulatory_systemhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-31https://en.wikipedia.org/wiki/Echinoderm#cite_note-31https://en.wikipedia.org/wiki/Echinoderm#cite_note-32https://en.wikipedia.org/wiki/Echinoderm#cite_note-wbd.etibioinformatics.nl-33https://en.wikipedia.org/wiki/Echinoderm#cite_note-34https://en.wikipedia.org/wiki/Open_circulatory_systemhttps://en.wikipedia.org/wiki/Hearthttps://en.wikipedia.org/wiki/Nitrogenous_wastehttps://en.wikipedia.org/wiki/Ammoniahttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Dorit791-21https://en.wikipedia.org/wiki/Nervous_systemhttps://en.wikipedia.org/wiki/Nervous_systemhttps://en.wikipedia.org/wiki/Nerve_nethttps://en.wikipedia.org/wiki/Brainhttps://en.wikipedia.org/wiki/Ganglionhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert885-26https://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert891-27https://en.wikipedia.org/wiki/Algaehttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert904-28https://en.wikipedia.org/wiki/Detritivorehttps://en.wikipedia.org/wiki/Cloacahttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert912-29https://en.wikipedia.org/wiki/Suspension_feederhttps://en.wikipedia.org/wiki/Planktonhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Ruppert920-30https://en.wikipedia.org/wiki/Body_cavityhttps://en.wikipedia.org/wiki/Circulatory_systemhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-31https://en.wikipedia.org/wiki/Echinoderm#cite_note-32https://en.wikipedia.org/wiki/Echinoderm#cite_note-wbd.etibioinformatics.nl-33https://en.wikipedia.org/wiki/Echinoderm#cite_note-34https://en.wikipedia.org/wiki/Open_circulatory_systemhttps://en.wikipedia.org/wiki/Hearthttps://en.wikipedia.org/wiki/Nitrogenous_wastehttps://en.wikipedia.org/wiki/Ammoniahttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Dorit791-21https://en.wikipedia.org/wiki/Nervous_systemhttps://en.wikipedia.org/wiki/Nerve_nethttps://en.wikipedia.org/wiki/Brainhttps://en.wikipedia.org/wiki/Ganglionhttps://en.wikipedia.org/wiki/Mollusc
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    movements of the organism and the synchronisation of the tube feet. Starfish have

    sensory cells in the epithelium and have simple eyespotsand touch-sensitive

    tentacle-li*e tube feet at the tips of their arms. Sea urchins have no particularsense organs but do have statocyststhat assist in gravitational orientation, and

    they have sensory cells in their epidermis, particularly in the tube feet, spines and

    pedicellariae. "rittle stars, crinoids and sea cucumbers in general do not have

    sensory organs but some burrowing sea cucumbers of theorderpodidahave a

    single statocyst ad8oining each radial nerve and some have an eyespot at the base

    of each tentacle.[+9!

    #he gonadsoccupy much of the body cavities of sea urchins and sea cucumbers,

    while the less voluminous crinoids, brittle stars and starfish have two gonads in

    each arm. :hile the primitive condition is considered to be the possession of one

    genital aperture, many organisms have multiple gonoporesthrough which eggs orsperm may be released.[+9!h

    Regeneration

    Sunflower starregenerating several arms

    ;any echinoderms have remar*able powers of regeneration. ;any species

    routinely autotomi&eand regenerate arms and viscera. Sea cucumbers often

    discharge parts of their internal organs if they perceive themselves to be

    threatened. #he discharged organs and tissues are regenerated over the course of

    several months. Sea urchins are constantly replacing spines lost through damage.Sea stars and sea lilies readily lose and regenerate their arms. In most cases, a

    single severed arm cannot grow into a new starfish in the absence of at least part

    of the disc.[+![+%![+![+(!4owever, in a few species a single arm can survive and

    develop into a complete individual[+%![+![+(!and in some species, the arms are

    intentionally detached for the purpose of ase$ual reproduction. uring periods

    when they have lost their digestive tracts, sea cucumbers live off stored nutrients

    and absorb dissolved organic matter directly from the water.[3!

    #he regeneration of lost parts involves both epimorphosisand morphalla$is.In

    epimorphosis stem cells

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    regeneration involves the movement and remodelling of e$isting tissues to replace

    lost parts. irect transdifferentiationof one type of tissue to another during tissue

    replacement is also observed.[31!

    #he robust larval growth is responsible for many echinoderms being used as

    popular model organismsin developmental biology.[32!

    https://en.wikipedia.org/wiki/Transdifferentiationhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Mashanov2005-41https://en.wikipedia.org/wiki/Model_organismhttps://en.wikipedia.org/wiki/Model_organismhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-42https://en.wikipedia.org/wiki/Transdifferentiationhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-Mashanov2005-41https://en.wikipedia.org/wiki/Model_organismhttps://en.wikipedia.org/wiki/Echinoderm#cite_note-42