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28.4: Superphylum Ecdysozoa

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    Ujuzi wa Kuendeleza

    • Eleza shirika la miundo ya nematodes
    • Kuelewa umuhimu wa Caenorhabditis elegans katika utafiti
    • Linganisha mifumo ya ndani na utaalamu wa kipengee cha phylum Arthropoda
    • Jadili umuhimu wa mazingira wa arthropods
    • Jadili sababu za mafanikio ya arthropod na wingi

    Ecdysozoa superphylum ina idadi kubwa ya aina. Hii ni kwa sababu ina makundi mawili ya wanyama mbalimbali: phylum Nematoda (roundworms) na Phylum Arthropoda (arthropodi). Kipengele kinachojulikana zaidi cha Ecdysozoans ni kifuniko chao cha nje kilichoitwa cuticle. Cuticle hutoa exoskeleton ngumu, lakini rahisi ambayo inalinda wanyama hawa kutokana na kupoteza maji, wadudu na mambo mengine ya mazingira ya nje. Wanachama wote wa superphylum hii mara kwa mara molt, au kumwaga cuticle yao kama wao kukua. Baada ya molting, wao hutoa cuticle mpya ambayo itaendelea mpaka awamu yao ya pili ya ukuaji. Mchakato wa molting na kuchukua nafasi ya cuticle inaitwa ecdysis, ambayo ni jinsi superphylum inayotokana na jina lake.

    Phylum Nematoda

    Nematoda, kama phyla wengine wengi wa wanyama, ni triploblastic na wana mesoderm ya embryonic ambayo iko kati ya ectoderm na endoderm. Wao pia ni bilaterally symmetrical, maana kwamba sehemu ya longitudinal itawagawanya katika pande za kulia na za kushoto ambazo zinalingana. Zaidi ya hayo, nematodes, au roundworms, wana pseudocoelom na hujumuisha aina zote za bure na za vimelea.

    Imesemekana kuwa jambo lisilo la nematode la biosphere limeondolewa, kutakuwa na kivuli cha ulimwengu wa zamani kwa namna ya nematodes. 1 Arthropods, mojawapo ya makundi mafanikio zaidi ya taxonomic duniani, ni viumbe vya coelomate vinavyojulikana na exoskeleton ngumu na appendages zilizounganishwa. Wote nematodo na arthropodi ni wa superphylum Ecdysozoa ambayo inaaminika kuwa clade yenye uzao wote wa mageuko kutoka kwa babu mmoja wa kawaida. Jina linatokana na neno ecdysis, ambalo linamaanisha kumwaga, au kutengeneza, ya exoskeleton. Phyla katika kundi hili wana cuticle ngumu ambayo inashughulikia miili yao, ambayo inapaswa kumwagika mara kwa mara na kubadilishwa kwao kuongezeka kwa ukubwa.

    Phylum Nematoda inajumuisha spishi zaidi ya 28,000 ikiwa na wastani wa 16,000 kuwa vimelea katika asili. Jina Nematoda linatokana na neno la Kigiriki “Nemos,” ambalo linamaanisha “thread” na linajumuisha mviringo. Nematodes zipo katika makazi yote na idadi kubwa ya watu binafsi wa kila aina iliyopo kila mmoja. Nematode ya bure, Caenorhabditis elegans imetumiwa sana kama mfumo wa mfano katika maabara duniani kote.

    Morpholojia

    Tofauti na cnidarians, nematodes zinaonyesha morphology tubular na sehemu ya mviringo. Wanyama hawa ni pseudocoelomates na kuonyesha uwepo wa mfumo kamili wa utumbo na mdomo tofauti na anus. Hii ni kinyume na cnidarians, ambapo ufunguzi mmoja tu umepo (mfumo usio kamili wa utumbo).

    Cuticle ya Nematodes ina matajiri katika collagen na polymer ya kabohydrate-protini inayoitwa chitin, na hufanya “mifupa” ya nje nje ya epidermis. Cuticle pia inaweka viungo vingi ndani, ikiwa ni pamoja na pharynx na rectum. Epidermis inaweza kuwa safu moja ya seli au syncytium, ambayo ni kiini cha multinucleated kilichoundwa kutoka kwa fusion ya seli zisizo na uninucleated.

    Morphology ya jumla ya minyoo hizi ni cylindrical, kama inavyoonekana katika Kielelezo\(\PageIndex{1}\). Kichwa ni radially symmetrical. Ufunguzi wa kinywa unapo kwenye mwisho wa anterior na midomo mitatu au sita pamoja na meno katika aina fulani kwa namna ya upanuzi wa cuticle. Baadhi ya nematodes zinaweza kuwasilisha marekebisho mengine ya nje kama pete, ngao za kichwa, au vidonge. Rings, hata hivyo, wala kutafakari kweli ndani ya mwili segmentation. Kinywa husababisha pharynx ya misuli na tumbo, ambayo inaongoza kwa ufunguzi wa rectum na anal katika mwisho wa nyuma. Misuli ya nematodes inatofautiana na yale ya wanyama wengi: Wana safu ya longitudinal tu, ambayo inashughulikia mwendo wa kuchapwa kama harakati zao.

    Picha a inaonyesha nematode yenye umbo la minyoo karibu na yai ya nematode yenye umbo la capsule. Mfano katika sehemu b unaonyesha sehemu ya msalaba wa nematode, ambayo ina kinywa upande mmoja na anus kwa upande mwingine. Kinywa huunganisha na pharynx, kisha kwa tumbo. Mishipa ya dorsal inaendesha juu ya mnyama na hujiunga na kichwa cha pete kama ganglia kwenye mwisho wa mbele. Majaribio yanaendesha kando ya tumbo kuelekea nyuma ya mnyama.
    Kielelezo\(\PageIndex{1}\): Kuchunguza micrograph ya elektroni inaonyesha (a) nematode ya soya ya cyst (Heterodera glycines) na yai ya nematode. (b) Uwakilishi wa schematic unaonyesha anatomy ya nematode ya kawaida. (mikopo a: muundo wa kazi na USDA ARS; data wadogo bar kutoka Matt Russell)

    Mfumo wa Excretory

    Katika nematodes, mifumo maalumu ya excretory haijaendelezwa vizuri. Taka za nitrojeni zinaweza kupotea kwa kutenganishwa kwa njia ya mwili mzima au kwenye pseudocoelom (cavity ya mwili), ambapo huondolewa na seli maalumu. Udhibiti wa maudhui ya maji na chumvi ya mwili hupatikana kwa tezi za renette, zilizopo chini ya pharynx katika nematodes za baharini.

    Mfumo wa neva

    Nematodes nyingi zina kamba nne za ujasiri za muda mrefu ambazo zinaendesha pamoja na urefu wa mwili katika nafasi za dorsal, ventral, na za nyuma. Kamba ya ujasiri ya mishipa ni bora zaidi kuliko kamba za dorsal au za nyuma. All nyuzi ujasiri fyuzi katika mwisho anterior, karibu koo, kuunda ganglia kichwa au “ubongo” wa minyoo (ambayo kuchukua fomu ya pete karibu koo) na pia katika mwisho posterior kuunda ganglia mkia. Katika C. elegans, mfumo wa neva akaunti kwa karibu theluthi moja ya jumla ya idadi ya seli katika wanyama.

    Uzazi

    Nematodes hutumia mikakati mbalimbali ya uzazi ambayo huanzia monoecious hadi dioecious hadi parthenogenic, kulingana na aina zinazozingatiwa. C. elegans ni spishi ya monoecious na inaonyesha maendeleo ya ova zilizomo katika uterasi pamoja na mbegu zilizomo katika spermatheca. Uterasi una ufunguzi wa nje unaojulikana kama vulva. Pore ya uzazi wa kike iko karibu katikati ya mwili, wakati kiume ni ncha. Miundo maalumu kwenye mkia wa dume humlinda mahali huku anaweka mbegu za kiume na spicules copulatory. Mbolea ni ya ndani, na maendeleo ya embryonic huanza hivi karibuni baada ya mbolea. Mtoto hutolewa kutoka kwenye vulva wakati wa hatua ya gastrulation. Hatua ya maendeleo ya kiinitete hudumu kwa masaa 14; maendeleo kisha inaendelea kupitia hatua nne za mfululizo wa mabuu na ecdysis kati ya kila hatua-L1, L2, L3, na L4—hatimaye kusababisha maendeleo ya mdudu mdogo wa kiume au wa kike mzima. Hali mbaya ya mazingira kama msongamano na ukosefu wa chakula inaweza kusababisha kuundwa kwa hatua ya kati ya mabuu inayojulikana kama lava ya dauer.

    Uunganisho wa kila siku: C. elegans: Mfumo wa Mfano wa Kuunganisha Mafunzo ya Maendeleo na Gen

    Kama wanabiolojia alitaka utafiti jinsi utegemezi nikotini yanaendelea katika mwili, jinsi lipids ni umewekwa, au kuchunguza kuvutia au repellant mali ya harufu fulani, wangeweza wazi haja ya kubuni majaribio matatu tofauti sana. Hata hivyo, wanaweza tu haja kitu kimoja cha utafiti: C. elegans. Caenorhabditis elegans ya nematode ililetwa katika lengo la utafiti mkuu wa kibiolojia na Dr. Sydney Brenner. Tangu 1963, Dk Brenner na wanasayansi duniani kote wametumia mnyama huyu kama mfumo wa mfano wa kujifunza taratibu mbalimbali za kisaikolojia na za maendeleo.

    C. elegans ni viumbe hai bure kupatikana katika udongo. Ni rahisi kulisha kiumbe hiki kwenye sahani za agar (minyoo 10,0/sahani), hula Escherichia coli (mwingine wa muda mrefu wa maabara ya kibiolojia duniani kote), na kwa hiyo, inaweza kukua kwa urahisi na kuhifadhiwa katika maabara. Mali kubwa ya nematode hii ni uwazi wake, ambayo husaidia watafiti kuchunguza na kufuatilia mabadiliko ndani ya mnyama kwa urahisi. Pia ni kiumbe rahisi chenye seli chache zaidi ya 1,000 na jenomu ya jeni 20,000. Inaonyesha shirika la chromosomal la DNA katika jozi tano za autosomes pamoja na jozi ya chromosomes za ngono, na kuifanya kuwa mgombea bora wa kujifunza maumbile. Kwa kuwa kila kiini kinaweza kutazamwa na kutambuliwa, kiumbe hiki ni muhimu kwa kusoma matukio ya seli kama mwingiliano wa kiini, uamuzi wa hatima ya seli, mgawanyiko wa seli, apoptosis, na usafiri wa ndani ya seli.

    Mali nyingine kubwa ni mzunguko mfupi wa maisha ya mdudu huu (Kielelezo\(\PageIndex{2}\)). Inachukua siku 3 tu kufikia “yai kwa watu wazima kwa yai ya binti;” Kwa hiyo, kufuatilia mabadiliko ya maumbile ni rahisi kwa mnyama huyu. Jumla ya maisha ya C. elegans ni wiki 2 hadi 3; hivyo, matukio yanayohusiana na umri ni rahisi kuchunguza. Kipengele kingine kinachofanya C. elegans mfumo bora wa majaribio ya mfano ni kwamba nafasi na idadi ya seli 959 zilizopo katika hermaphrodites ya watu wazima wa kiumbe hiki ni mara kwa mara. Kipengele hiki ni muhimu sana wakati wa kusoma upambanuzi wa seli, mawasiliano ya kiini-kiini, na apoptosis. Mwishowe, C. elegans pia ni amenable kwa manipulations maumbile kwa kutumia mbinu Masi, kuzungusha mbali manufaa yake kama mfumo mfano.

    Wanabiolojia duniani kote wameunda mabenki ya habari na makundi yaliyojitolea kwa utafiti kwa kutumia C. elegans. Matokeo yao yamesababisha, kwa mfano, kwa uelewa bora wa mawasiliano ya seli wakati wa maendeleo, ishara ya neuronal na ufahamu katika udhibiti wa lipid (ambayo ni muhimu katika kushughulikia masuala ya afya kama maendeleo ya fetma na ugonjwa wa kisukari). Katika miaka ya hivi karibuni, tafiti zimewaangazia jamii ya matibabu na ufahamu bora wa ugonjwa wa figo wa polycystic. Kiumbe hiki rahisi kimepelekea wanabiolojia kwa matokeo magumu na muhimu, kukua uwanja wa sayansi kwa njia zinazogusa ulimwengu wa kila siku.

    Picha inaonyesha mdudu wa uwazi kuhusu millimeter kwa urefu. Mchoro B unaonyesha mzunguko wa maisha ya C. elegans, ambayo huanza wakati yai inapokwisha, ikitoa vijana wa L1. Baada ya masaa 12 vijana wa L1 hubadilika kuwa vijana wa L2. Baada ya masaa 7 vijana wa L2 hubadilika kuwa vijana wa L3. Baada ya masaa mengine 7 vijana wa L3 hubadilika kuwa vijana wa L4. Baada ya masaa 14 vijana wa L4 hubadilika kuwa mtu mzima. Hermaphroditic watu wazima wenzi na mtu mwingine mzima kuzalisha mayai mbolea ambayo hatch, kukamilisha mzunguko.
    Kielelezo\(\PageIndex{2}\): (a) Micrograph hii ya mwanga inaonyesha Caenorhabditis elegans. Hatua yake ya watu wazima ya uwazi ina seli 959 hasa. (b) Mzunguko wa maisha ya C. elegans ina hatua nne za vijana (L1 hadi L4) na hatua ya watu wazima. Chini ya hali nzuri, nematode hutumia muda uliowekwa katika kila hatua ya vijana, lakini chini ya hali ya shida, inaweza kuingia hali ya dauer ambayo haina umri. Mdudu ni hermaphroditic katika hali ya watu wazima, na kuunganisha minyoo miwili hutoa yai ya mbolea. (mikopo a: mabadiliko ya kazi na “snickclunk” /Flickr: mikopo b: mabadiliko ya kazi na NIDDK, NIH; data ya kiwango cha bar kutoka Matt Russell)

    Idadi ya nematodes ya kawaida ya vimelea hutumika kama mifano kuu ya parasitism. Wanyama hawa huonyesha maisha magumu ambayo yanahusisha majeshi mengi, na wanaweza kuwa na athari muhimu za matibabu na mifugo. Binadamu wanaweza kuambukizwa na Dracunculus medinensis, inayojulikana kama minyoo ya Guinea, wanaponywa maji yasiyochujwa yaliyo na copepods (Kielelezo\(\PageIndex{3}\)). Vidonge, kama vile Ancyclostoma na Necator, huambukiza matumbo na kulisha damu ya mamalia, hasa katika mbwa, paka, na wanadamu. Vidudu vya Trichina (Trichinella) ni kiumbe cha causal cha trichinosis kwa wanadamu, mara nyingi husababishwa na matumizi ya nyama ya nguruwe isiyopikwa; Trichinella inaweza kuambukiza majeshi mengine ya mamalia pia. Ascaris, mviringo mkubwa wa intestinal, huiba lishe kutoka kwa mwenyeji wake wa binadamu na inaweza kuunda uzuiaji wa kimwili wa matumbo. Vidudu vya filarial, kama vile Dirofilaria na Wuchereria, huwa vectored na mbu, ambazo hupita mawakala wa kuambukiza kati ya wanyama kupitia shughuli zao za kunyonya damu. Dirofilaria immitis, vimelea vya damu, ni aina mbaya ya moyo wa mbwa. Wuchereria bancrofti huathiri lymph nodes ya binadamu, na kusababisha hali isiyo ya lethal lakini deforming iitwayo elephantiasis, ambapo sehemu za mwili kuwa kuvimba kwa idadi kubwa kutokana na kizuizi cha mifereji ya lymphatic na kuvimba kwa tishu za lymphatic.

    Sehemu ya A inaonyesha mguu na mdudu wa Guinea unaoenea kutoka kwenye malengelenge. Mwisho wa mdudu umefungwa karibu na fimbo. Sehemu ya B inaonyesha mzunguko wa maisha ya mdudu wa Guinea, ambayo huanza wakati mtu hunywa maji yasiyochujwa yaliyo na copepods iliyoambukizwa na mabuu ya minyoo ya Guinea. Mabuu, ambayo hutolewa wakati copepods kufa, kupenya ukuta wa tumbo na tumbo. Minyoo hukomaa na kuzaa. Wanawake wenye mbolea huhamia kwenye uso wa ngozi, ambapo hutoa mabuu ndani ya maji. Copepods hutumia mabuu. Copepods hutumiwa na wanadamu, kukamilisha mzunguko. Karibu mwaka baada ya kuambukizwa, mdudu wa kike hutoka kwenye ngozi.
    Kielelezo\(\PageIndex{3}\): Minyoo ya Guinea Dracunculus medinensis huathiri watu milioni 3.5 kila mwaka, hasa Afrika. (a) Hapa, mdudu umefungwa karibu na fimbo ili uweze kuondolewa. (b) Maambukizi hutokea wakati watu hutumia maji yaliyotokana na copepods zilizoambukizwa, lakini hii inaweza kuzuiwa kwa urahisi na mifumo rahisi ya filtration. (mikopo: mabadiliko ya kazi na CDC)

    Phylum Arthropoda

    Jina “arthropoda” linamaanisha “miguu iliyounganishwa” (kwa Kigiriki, “arthros” inamaanisha “pamoja” na “podos” inamaanisha “mguu”); inaelezea kwa usahihi idadi kubwa ya uti wa mgongo uliojumuishwa katika phylum hii. Arthropoda inatawala ufalme wa wanyama ikiwa na wastani wa asilimia 85 ya spishi zinazojulikana zilizojumuishwa katika fylamu hii na arthropodi nyingi bado hazina kumbukumbu. Tabia kuu za wanyama wote katika phylum hii ni sehemu ya kazi ya mwili na uwepo wa appendages zilizounganishwa. Arthropods pia huonyesha kuwepo kwa exoskeleton iliyofanywa hasa ya chitini, ambayo ni polysaccharide isiyo na maji, ngumu. Phylum Arthropoda ni phylum kubwa katika ulimwengu wa wanyama, na wadudu huunda tabaka moja kubwa ndani ya phylum hii. Arthropods ni eucoelomate, viumbe vya protostomic.

    Phylum Arthropoda inajumuisha wanyama ambao wamefanikiwa katika kutawala makazi ya duniani, majini, na angani. Phylum hii inaainishwa zaidi katika subphyla tano: Trilobitomorpha (trilobites, yote haipo), Hexapoda (wadudu na jamaa), Myriapoda (millipedes, centipedes, na jamaa), Wakrustaceans (kaa, lobsters, crayfish, isopods, barnacles, na baadhi ya zooplankton), na Chelicerata (kaa ya farasi, arachnids, nge, na baba longlegs). Trilobiti ni kundi la kutoweka la arthropodi linalopatikana hasa katika zama za kabla ya Kambrian ambazo pengine zinahusiana kwa karibu zaidi na Wakelicerata. Hizi zinatambuliwa kulingana na rekodi za mafuta (Kielelezo\(\PageIndex{4}\)).

    Trilobite ya fossilized inafanana na mguu, na mwisho wa mviringo wa mbele na matuta yanayotembea kote mwili.
    Kielelezo\(\PageIndex{4}\): Trilobites, kama moja katika mafuta haya, ni kundi la mwisho la arthropods. (mikopo: Kevin Walsh)

    Morpholojia

    Kipengele cha pekee cha wanyama katika phylum ya arthropod ni uwepo wa mwili uliogawanyika na fusion ya seti ya makundi ambayo hutoa mikoa ya mwili ya kazi inayoitwa tagma. Tagma inaweza kuwa katika mfumo wa kichwa, thorax, na tumbo, au cephalothorax na tumbo, au kichwa na shina. Cavity ya kati, inayoitwa hemocoel (au cavity ya damu), iko, na mfumo wa mzunguko wa wazi umewekwa na moyo wa tubular au moja-chambered. Mifumo ya upumuaji inatofautiana kulingana na kundi la arthropod: wadudu na myriapodi hutumia mfululizo wa zilizopo (tracheae) ambazo zina tawi kupitia mwili, wazi kwa nje kupitia fursa zinazoitwa spiracles, na hufanya kubadilishana gesi moja kwa moja kati ya seli na hewa katika tracheae, ilhali crustaceans ya majini hutumia gills, chelicerates duniani kuajiri mapafu kitabu, na chelicerates majini kutumia kitabu gills (Kielelezo\(\PageIndex{5}\)). Kitabu cha mapafu ya arachnids (scorpions, buibui, kupe na vimelea) vina stack ya wima ya tishu za ukuta wa hemocoel ambazo zinafanana na kurasa za kitabu. Kati ya kila “kurasa” za tishu ni nafasi ya hewa. Hii inaruhusu pande zote mbili za tishu kuwasiliana na hewa wakati wote, na kuongeza ufanisi wa kubadilishana gesi. Gills ya crustaceans ni miundo filamentous ambayo kubadilishana gesi na maji ya jirani. Vikundi vya arthropods pia hutofautiana katika viungo vinavyotumika kwa excretion, huku crustaceans wanao tezi za kijani na wadudu wanaotumia mirija ya Malpighian, ambayo hufanya kazi kwa kushirikiana na hindgut ili kurejesha maji huku wakiondoa mwili wa taka za nitrojeni. Cuticle ni kifuniko cha arthropod. Inajumuisha tabaka mbili: epicuticle, ambayo ni safu nyembamba, isiyo na sugu ya maji isiyo na chitin, na safu chini yake, procuticle ya chitinous. Chitin ni polysaccharide ngumu, rahisi. Ili kukua, arthropod inapaswa kumwaga exoskeleton wakati wa mchakato unaoitwa ecdysis (“kuondokana”); hii ni njia mbaya ya ukuaji, na wakati huu, mnyama ana hatari ya predation. Morphology ya tabia ya wanyama mwakilishi kutoka kila subphylum ni ilivyoelezwa hapo chini.

    Sehemu A ni mchoro wa buibui unaoonyesha muhtasari wa mwili, na moyo na mapafu ndani. Kitabu cha mapafu kinaonekana kama kitabu kilicho na kurasa nyingi na iko tu anterior kwa spiracle katika tumbo la tumbo. Moyo ni tube ndefu iko katika sehemu ya dorsal ya tumbo. Sehemu ya B ni picha ya chini ya kaa ya farasi. Gills ya kitabu ni jozi 5 za sahani karibu na mkia.
    Kielelezo\(\PageIndex{5}\): Mapafu ya kitabu cha (a) arachnids yanajumuisha mifuko ya hewa na tishu za hemocoel zilizoumbwa kama stack ya vitabu. Kitabu gills ya (b) crustaceans ni sawa na kitabu mapafu lakini ni nje ili kubadilishana gesi kunaweza kutokea kwa maji ya jirani. (mikopo a: mabadiliko ya kazi na Ryan Wilson kulingana na kazi ya awali na John Henry Comstock; mikopo b: mabadiliko ya kazi na Angel Schatz)

    Subphylum Hexapoda

    Jina Hexapoda linaashiria kuwepo kwa miguu sita (jozi tatu) katika wanyama hawa kama kutofautishwa na idadi ya jozi zilizopo katika arthropodi nyingine. Hexapods ni sifa ya kuwepo kwa kichwa, thorax, na tumbo, ikiwa ni tagma tatu. Thorax huzaa mabawa pamoja na miguu sita katika jozi tatu. Wengi wa wadudu wa kawaida tunaokutana kila siku—ikiwa ni pamoja na mchwa, mende, vipepeo, na nzi-ni mifano ya Hexapoda.

    Miongoni mwa hexapods, wadudu (Kielelezo\(\PageIndex{6}\)) ni darasa kubwa katika suala la aina tofauti kama vile majani katika makazi ya duniani. Kwa kawaida, kichwa huzaa jozi moja ya antenna za hisia, mandibles kama mouthparts, jozi ya macho ya kiwanja, na baadhi ya ocelli (macho rahisi) pamoja na nywele nyingi za hisia. Thorax huzaa jozi tatu za miguu (jozi moja kwa sehemu) na jozi mbili za mbawa, na jozi moja kila mmoja kwenye makundi ya pili na ya tatu ya thoracic. Kwa kawaida tumbo ina makundi kumi na moja na huzaa apertures ya uzazi. Hexapoda inajumuisha wadudu ambao wana mabawa (kama nzi za matunda) na wasio na mabawa (kama fleas).

    Mfano unaonyesha anatomy ya nyuki. Mfumo wa utumbo una kinywa, pharynx, tumbo, tumbo, na anus. Mfumo wa upumuaji una spiracles, au fursa, upande wa mwili wa nyuki zinazoungana na zilizopo zinazoendesha juu na kujiunga na tube kubwa ya uti wa mgongo inayounganisha spiracles zote pamoja. Mfumo wa mzunguko una chombo cha damu cha dorsal ambacho kina mioyo mingi kwa urefu wake. Mfumo wa neva una ganglia ya ubongo katika kichwa kinachounganisha kwenye kamba ya ujasiri wa tumbo.
    Kielelezo\(\PageIndex{6}\): Katika anatomy hii ya msingi ya wadudu wa hexapod, kumbuka kuwa wadudu wana mfumo wa utumbo (njano), mfumo wa kupumua (bluu), mfumo wa mzunguko (nyekundu), na mfumo wa neva (nyekundu).

    Zoezi\(\PageIndex{1}\)

    Ni ipi kati ya taarifa zifuatazo kuhusu wadudu ni uongo?

    1. Vidudu vina mishipa ya damu ya dorsal na ya mviringo.
    2. Vidudu vina spiracles, fursa zinazowezesha hewa kuingia.
    3. Trachea ni sehemu ya mfumo wa utumbo.
    4. Vidudu vina mfumo wa utumbo ulioendelea na mdomo, mazao, na tumbo.
    Jibu

    c

    Subphylum Myriapoda

    Subphylum Myriapoda inajumuisha arthropods yenye miguu mingi. Ingawa jina ni hyperbolic katika kupendekeza kwamba miguu elfu kumi iko katika uti wa mgongo hizi, idadi ya miguu inaweza kutofautiana kutoka 10 hadi 750. Subphylamu hii inajumuisha spishi 13,000; mifano inayopatikana kwa kawaida ni millipedes na centipedes. Myriapods wote ni wanyama duniani na wanapendelea mazingira ya baridi.

    Myriapods kawaida hupatikana katika udongo unyevu, kuoza nyenzo za kibiolojia, na takataka ya majani. Subphylum Myriapoda imegawanyika katika madarasa manne: Chilopoda, Symphyla, Diplopoda, na Pauropoda. Centipedes kama Scutigera coleoptrata (Kielelezo 28.4.7) huainishwa kama chilopods. Wanyama hawa hubeba jozi moja ya miguu kwa kila sehemu, mandibles kama mouthparts, na ni kiasi fulani dorsoventrally flattened. Miguu katika sehemu ya kwanza imebadilishwa kuunda forcipules (makucha ya sumu) ambayo hutoa sumu kwa mawindo kama buibui na mende, kwani wanyama hawa wote wanakula. Millipedes kubeba jozi mbili za miguu kwa diplosegment, kipengele kwamba matokeo ya fusion embryonic ya jozi karibu ya makundi ya mwili, ni kawaida rounder katika sehemu nzima, na ni herbivores au detritivores. Millipedes ina idadi kubwa ya miguu ikilinganishwa na centipedes, ingawa hawana kubeba miguu elfu (Kielelezo\(\PageIndex{7}\)).

    Picha inaonyesha centipede na miguu mingi, ndefu sana.Picha inaonyesha millipede yenye rangi ya kijani na kahawia iliyopigwa karibu yenyewe. Ina miguu mingi kidogo.
    Kielelezo\(\PageIndex{7}\): (a) The Scutigera coleoptrata centipede has up to 15 pairs of legs. (b) This North American millipede (Narceus americanus) bears many legs, although not a thousand, as its name might suggest. (credit a: modification of work by Bruce Marlin; credit b: modification of work by Cory Zanker)

    Subphylum Crustacea

    Crustaceans are the most dominant aquatic arthropods, since the total number of marine crustacean species stands at 67,000, but there are also freshwater and terrestrial crustacean species. Krill, shrimp, lobsters, crabs, and crayfish are examples of crustaceans (Figure \(\PageIndex{8}\)). Terrestrial species like the wood lice (Armadillidium spp.) (also called pill bugs, rolly pollies, potato bugs, or isopods) are also crustaceans, although the number of non-aquatic species in this subphylum is relatively low.

    Photo a shows a crab on land, and photo b shows a bright red shrimp in the water.
    Figure \(\PageIndex{8}\): The (a) crab and (b) shrimp krill are both crustaceans. (credit a: modification of work by William Warby; credit b: modification of work by Jon Sullivan)

    Crustaceans possess two pairs of antennae, mandibles as mouthparts, and biramous (“two branched”) appendages, which means that their legs are formed in two parts, as distinct from the uniramous (“one branched”) myriapods and hexapods (Figure \(\PageIndex{9}\)).

    Illustration A shows the biramous, or two-branched leg of a crayfish. Illustration B shows the uniramous, or one-branched leg of an insect.
    Figure \(\PageIndex{9}\): Arthropods may have (a) biramous (two-branched) appendages or (b) uniramous (one-branched) appendages. (credit b: modification of work by Nicholas W. Beeson)

    Unlike that of the Hexapoda, the head and thorax of most crustaceans is fused to form a cephalothorax (Figure \(\PageIndex{10}\)), which is covered by a plate called the carapace, thus producing a body structure of two tagma. Crustaceans have a chitinous exoskeleton that is shed by molting whenever the animal increases in size. The exoskeletons of many species are also infused with calcium carbonate, which makes them even stronger than in other arthropods. Crustaceans have an open circulatory system where blood is pumped into the hemocoel by the dorsally located heart. Hemocyanin and hemoglobin are the respiratory pigments present in these animals.

    An illustration of a midsagittal cross section of a crayfish shows the carapace around the cephalothorax, and the heart in the dorsal thorax area.
    Figure \(\PageIndex{10}\): The crayfish is an example of a crustacean. It has a carapace around the cephalothorax and the heart in the dorsal thorax area. (credit: Jane Whitney)

    Most crustaceans are dioecious, which means that the sexes are separate. Some species like barnacles may be hermaphrodites. Serial hermaphroditism, where the gonad can switch from producing sperm to ova, may also be seen in some species. Fertilized eggs may be held within the female of the species or may be released in the water. Terrestrial crustaceans seek out damp spaces in their habitats to lay eggs.

    Larval stages—nauplius and zoea—are seen in the early development of crustaceans. A cypris larva is also seen in the early development of barnacles (Figure \(\PageIndex{11}\)).

    Micrograph a shows a shrimp nauplius larva, which has a teardrop-shaped body with tentacles and long, frilly arms at the wide end. Micrograph b shows a barnacle cypris larva, which is similar in shape to a clam. Micrograph c shows green crab zoea larva, which resembles a shrimp.
    Figure \(\PageIndex{11}\): All crustaceans go through different larval stages. Shown are (a) the nauplius larval stage of a tadpole shrimp, (b) the cypris larval stage of a barnacle, and (c) the zoea larval stage of a green crab. (credit a: modification of work by USGS; credit b: modification of work by Mª. C. Mingorance Rodríguez; credit c: modification of work by B. Kimmel based on original work by Ernst Haeckel)

    Crustaceans possess a tripartite brain and two compound eyes. Most crustaceans are carnivorous, but herbivorous and detritivorous species are also known. Crustaceans may also be cannibalistic when extremely high populations of these organisms are present.

    Subphylum Chelicerata

    This subphylum includes animals such as spiders, scorpions, horseshoe crabs, and sea spiders. This subphylum is predominantly terrestrial, although some marine species also exist. An estimated 77,000 species are included in subphylum Chelicerata. Chelicerates are found in almost all habitats.

    The body of chelicerates may be divided into two parts: prosoma and opisthosoma, which are basically the equivalents of cephalothorax (usually smaller) and abdomen (usually larger). A “head” tagmum is not usually discernible. The phylum derives its name from the first pair of appendages: the chelicerae (Figure \(\PageIndex{12}\)), which are specialized, claw-like or fang-like mouthparts. These animals do not possess antennae. The second pair of appendages is known as pedipalps. In some species, like sea spiders, an additional pair of appendages, called ovigers, is present between the chelicerae and pedipalps.

    The photo shows a black, shiny scorpion with very large chelicerae, or pincers.
    Figure \(\PageIndex{12}\): The chelicerae (first set of appendages) are well developed in the scorpion. (credit: Kevin Walsh)

    Chelicerae are mostly used for feeding, but in spiders, these are often modified into fangs that inject venom into their prey before feeding (Figure \(\PageIndex{13}\)). Members of this subphylum have an open circulatory system with a heart that pumps blood into the hemocoel. Aquatic species have gills, whereas terrestrial species have either trachea or book lungs for gaseous exchange.

    The photo shows a spider with a thick, hairy body and eight long legs.
    Figure \(\PageIndex{13}\): The trapdoor spider, like all spiders, is a member of the subphylum Chelicerata. (credit: Marshal Hedin)

    Most chelicerates ingest food using a preoral cavity formed by the chelicerae and pedipalps. Some chelicerates may secrete digestive enzymes to pre-digest food before ingesting it. Parasitic chelicerates like ticks and mites have evolved blood-sucking apparatuses.

    The nervous system in chelicerates consists of a brain and two ventral nerve cords. These animals use external fertilization as well as internal fertilization strategies for reproduction, depending upon the species and its habitat. Parental care for the young ranges from absolutely none to relatively prolonged care.

    Summary

    Nematodes are pseudocoelomate animals akin to flatworms, yet display more advanced neuronal development, a complete digestive system, and a body cavity. This phylum includes free-living as well as parasitic organisms like Caenorhabditis elegans and Ascaris spp., respectively. They include dioeceous as well as hermaphroditic species. Nematodes also possess an excretory system that is not quite well developed. Embryonic development is external and proceeds via three larval stages. A peculiar feature of nematodes is the secretion of a collagenous/chitinous cuticle outside the body.

    Arthropods represent the most successful phylum of animal on Earth, in terms of the number of species as well as the number of individuals. These animals are characterized by a segmented body as well as the presence of jointed appendages. In the basic body plan, a pair of appendages is present per body segment. Within the phylum, traditional classification is based on mouthparts, number of appendages, and modifications of appendages present. Arthropods bear a chitinous exoskeleton. Gills, trachea, and book lungs facilitate respiration. Sexual dimorphism is seen in this phylum, and embryonic development includes multiple larval stages.

    Footnotes

    1. 1 Stoll, N. R., “This wormy world. 1947,” Journal of Parasitology 85(3) (1999): 392-396.

    Glossary

    Arthropoda
    phylum of animals with jointed appendages
    biramous
    referring to two branches per appendage
    cephalothorax
    fused head and thorax in some species
    chelicera
    modified first pair of appendages in subphylum Chelicerata
    cuticle (animal)
    the tough, external layer possessed by members of the invertebrate class Ecdysozoa that is periodically molted and replaced
    cypris
    larval stage in the early development of crustaceans
    hemocoel
    internal body cavity seen in arthropods
    hermaphrodite
    referring to an animal where both male and female gonads are present in the same individual
    nauplius
    larval stage in the early development of crustaceans
    Nematoda
    phylum of worm-like animals that are triploblastic, pseudocoelomates that can be free-living or parasitic
    oviger
    additional pair of appendages present on some arthropods between the chelicerae and pedipalps
    pedipalp
    second pair of appendages in Chelicerata
    uniramous
    referring to one branch per appendage
    zoea
    larval stage in the early development of crustaceans