海參綱分為楯手目(Aspidochirotida)和平足目(Elasipodida)。
楯手目楯形(xing)觸手10—30個,多為(wei)20個;體(ti)(ti)呈圓筒狀,腹(fu)面(mian)常(chang)呈足底(di)狀,背面(mian)和(he)腹(fu)面(mian)常(chang)明顯(xian)有區別,特別是疣足明顯(xian)的種類(lei);無翻頸部和(he)收(shou)縮肌;縱肌5對;生殖腺(xian)一(yi)束(shu)或兩束(shu),位于腸系(xi)膜的--側(ce)或兩側(ce);有呼吸樹;常(chang)有居(ju)維(wei)氏器(qi);骨片常(chang)為(wei)桌形(xing)體(ti)(ti)、扣(kou)狀體(ti)(ti)或花紋樣(yang)體(ti)(ti)等。
平(ping)足目(mu)體(ti)形常明顯兩側對稱,有(you)(you)(you)的具(ju)大(da)錐形疣足,有(you)(you)(you)的身(shen)體(ti)周圍有(you)(you)(you)邊緣,有(you)(you)(you)的具(ju)尾部。觸手楯形或葉狀,數(shu)目(mu)10—20個(ge);有(you)(you)(you)管足,但數(shu)目(mu)不多。無收(shou)縮肌和呼吸樹。后腸的腸系膜附著在右(you)背間步帶,常靠近右(you)背縱肌附近。
蛇尾綱分為真蛇尾目(mu)(OPHIURIDA)和蜍(chu)蛇尾目(mu)(PHRYNOPHIURIDA)。蛇尾綱(Ophiuroidea),體盤(pan)與各(ge)(ge)腕(wan)區分極為明顯。腕(wan)細長,可(ke)彎曲。無步帶溝,管足二列,不具(ju)吸盤(pan)及要(yao)。各(ge)(ge)腕(wan)由(you)四列骨板包(bao)圍(wei),腕(wan)內還(huan)有一列腕(wan)骨。肌肉發達,活(huo)動自如(ru)。篩板位于口面。
消化道退化,食(shi)道短,后連盲囊(nang)狀的胃。無腸,無肛門(men)。雌雄異體,幼(you)蟲稱蛇尾幼(you)蟲。如陽遂(sui)足、刺蛇尾等。
海星綱( Asteroidea),體(ti)扁平(ping),多為五輻射對稱,體(ti)盤和腕(wan)分界不明(ming)顯。生活時(shi)口面(mian)(mian)向下,反(fan)口面(mian)(mian)向上。腕(wan)的(de)口面(mian)(mian)中(zhong)央具(ju)(ju)步帶溝,溝內有管足。內骨(gu)骼的(de)骨(gu)板以結締組織相連,柔(rou)韌可彎曲。體(ti)表具(ju)(ju)棘和叉棘,為骨(gu)骼的(de)突起。具(ju)(ju)皮鰓,水管系發達。個體(ti)發育中(zhong)經羽腕(wan)幼蟲(chong)和短腕(wan)幼蟲(chong)。
海(hai)膽綱(gang)( Echinoidea)體呈(cheng)球形,盤形或心臟形。口(kou)面向(xiang)下,口(kou)位(wei)于(yu)中(zhong)央(yang);反口(kou)面中(zhong)央(yang)為(wei)(wei)肛(gang)門(men)。口(kou)與反口(kou)面之(zhi)間相間排列著(zhu)骨(gu)板(ban)(ban)(ban)組(zu)成的5個具管足(zu)的步帶(dai)區(qu)和(he)5個無管足(zu)的間步帶(dai)區(qu),各骨(gu)板(ban)(ban)(ban)上(shang)均有疣突和(he)可(ke)動的長棘。圍(wei)(wei)肛(gang)部周圍(wei)(wei)由5個生(sheng)殖(zhi)板(ban)(ban)(ban)( gential plate)和(he)5個眼(yan)板(ban)(ban)(ban)( ocular plate)組(zu)成。生(sheng)殖(zhi)板(ban)(ban)(ban)上(shang)各有一(yi)生(sheng)殖(zhi)孔(kong),有一(yi)塊生(sheng)殖(zhi)板(ban)(ban)(ban)多孔(kong),形狀特(te)異(yi),兼有篩(shai)板(ban)(ban)(ban)的作用(yong)。眼(yan)板(ban)(ban)(ban)上(shang)各有一(yi)眼(yan)孔(kong),輻水管末端自孔(kong)伸出,為(wei)(wei)感覺器。
口位于口面圍(wei)中央,口腔內由骨(gu)板(ban)、齒及(ji)肌肉(rou)骨(gu)板(ban)組成(cheng)結(jie)構(gou)復雜的咀嚼器,稱亞里斯多德(de)提燈(deng)( Aristotle lantern)。
海百合(he)綱(gang)( Crinoidea) (代表動物(wu):海百合(he))現存棘(ji)皮(pi)動物(wu)中(zhong)最為古老的一綱(gang)。暫時或終身營(ying)固著生活。口(kou)與肛門都朝上,腕分枝(zhi)似羽,管足呈(cheng)觸手狀(zhuang)。幼體呈(cheng)桶狀(zhuang)。全世界約有(you)610種。體有(you)柄(海百合(he)類(lei))或成體無柄(海羊(yang)齒類(lei)),頗似植物(wu)。具(ju)有(you)分枝(zhi)的腕。步帶溝內生觸手,無運(yun)動功能,可捕食(shi)。雌雄異體,生殖腺位于生殖羽內。個(ge)體發育經過蛹形的樽形幼蟲(chong)階段(duan)。
棘皮動物外(wai)觀差別很(hen)大,有(you)星狀(zhuang)、球狀(zhuang)、圓筒狀(zhuang)和(he)(he)花狀(zhuang)。成(cheng)體五放(fang)輻射(she)(she)對(dui)(dui)稱,由(you)管(guan)(guan)足排(pai)列表(biao)現出來。根據管(guan)(guan)足的(de)(de)有(you)無,身體區分為有(you)管(guan)(guan)足的(de)(de)輻部或(huo)步帶和(he)(he)無管(guan)(guan)足的(de)(de)間(jian)輻部或(huo)間(jian)步帶。內部器官,包括水(shui)管(guan)(guan)系、神經(jing)系、血系和(he)(he)生殖系均為輻射(she)(she)對(dui)(dui)稱,只(zhi)有(you)消化道除外(wai)。由(you)于(yu)輻射(she)(she)對(dui)(dui)稱,身體有(you)口面和(he)(he)反口面之(zhi)分。
盡(jin)管(guan)本門各綱(gang)動物體形有很(hen)大差別,但其基本構造十分一致。海(hai)星和蛇尾類呈(cheng)星形,上下(xia)扁(bian)平,體軸(zhou)很(hen)短,口面(mian)(mian)朝下(xia),管(guan)足(zu)沿著腕(輻部)作放射狀排列。海(hai)膽和海(hai)參體軸(zhou)延長(chang),輻部和間輻部結(jie)合,體呈(cheng)球形或圓筒形,管(guan)足(zu)作子午線排列。海(hai)百(bai)合口面(mian)(mian)向(xiang)上,反(fan)口面(mian)(mian)具長(chang)柄或卷枝(zhi)供附著用(yong)。
棘皮(pi)動物骨骼很發(fa)達,由許多分(fen)開的(de)(de)碳酸鈣骨板構成(cheng),各板均(jun)由一單晶的(de)(de)方解石(shi)組成(cheng)。骨骼外(wai)包表皮(pi),皮(pi)上一般帶棘。海(hai)(hai)膽(dan)和海(hai)(hai)星有(you)不(bu)(bu)同的(de)(de)叉棘。海(hai)(hai)膽(dan)骨骼最為發(fa)達,骨板密切(qie)愈(yu)合(he)成(cheng)殼(ke)。海(hai)(hai)星、蛇尾和海(hai)(hai)百(bai)合(he)的(de)(de)腕骨板成(cheng)椎(zhui)骨狀(zhuang)。海(hai)(hai)參骨骼最不(bu)(bu)發(fa)達,變為微小的(de)(de)分(fen)散骨針或(huo)骨片。
大多底棲,少數海參營浮游生活(huo);自由(you)生活(huo)的種類能夠緩慢(man)移動。攝(she)食(shi)方式為吞食(shi)性(xing)、濾食(shi)性(xing)和肉食(shi)性(xing)。
棘皮動物(wu)多(duo)為雌雄(xiong)異體(ti),生(sheng)殖細胞釋放(fang)到(dao)海水(shui)中受精,幼體(ti)在初發生(sheng)時形狀相(xiang)同,以后(hou)則隨綱(gang)而異,少數(shu)種(zhong)類(lei)可行無性裂體(ti)繁殖。對水(shui)質污染很敏感,再(zai)生(sheng)力一般很強。
有(you)些(xie)棘皮動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)是(shi)(shi)珍貴(gui)食(shi)品,如海(hai)(hai)參、海(hai)(hai)膽(dan)卵。在海(hai)(hai)洋生態系統(tong)內,棘皮動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)在某(mou)(mou)(mou)些(xie)底(di)棲(qi)動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)群落中,常為(wei)優(you)勢種(zhong)(zhong)。在深淵(yuan)海(hai)(hai)底(di)的(de)(de)底(di)棲(qi)動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)生物(wu)(wu)(wu)量中,棘皮動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)最高可(ke)(ke)占90%。在研(yan)究(jiu)海(hai)(hai)洋動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)地(di)理學上(shang),棘皮動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)常是(shi)(shi)很好(hao)的(de)(de)指標種(zhong)(zhong)。某(mou)(mou)(mou)些(xie)吞食(shi)性(xing)種(zhong)(zhong)類(lei)能(neng)夠(gou)大(da)量搬運腐(fu)敗物(wu)(wu)(wu)質(zhi),能(neng)減少海(hai)(hai)底(di)微生物(wu)(wu)(wu)的(de)(de)活(huo)動(dong)(dong)(dong)(dong)。某(mou)(mou)(mou)些(xie)鉆(zhan)石的(de)(de)種(zhong)(zhong)類(lei)對海(hai)(hai)岸線造成破壞。某(mou)(mou)(mou)些(xie)蛇尾(wei)類(lei)常是(shi)(shi)底(di)棲(qi)魚類(lei)的(de)(de)餌料(liao)。海(hai)(hai)星喜吃(chi)貝類(lei),在貝類(lei)養殖上(shang)常是(shi)(shi)敵害。棘皮動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)化石種(zhong)(zhong)類(lei)甚多,在地(di)質(zhi)學上(shang)占有(you)一定地(di)位。有(you)的(de)(de)石灰石地(di)層全部由(you)分解了的(de)(de)海(hai)(hai)百(bai)合骨骼構(gou)成。在實(shi)驗胚胎學等基礎理論(lun)研(yan)究(jiu)方面(mian),海(hai)(hai)膽(dan)卵是(shi)(shi)很好(hao)的(de)(de)實(shi)驗材料(liao)之一。某(mou)(mou)(mou)些(xie)棘皮動(dong)(dong)(dong)(dong)物(wu)(wu)(wu)具有(you)毒腺或毒液,有(you)可(ke)(ke)能(neng)通過研(yan)究(jiu)發展成藥(yao)物(wu)(wu)(wu)。從幾種(zhong)(zhong)海(hai)(hai)參分離(li)出(chu)的(de)(de)海(hai)(hai)參素和粘多糖具有(you)抗癌(ai)活(huo)性(xing)。