Acoelomorpha
Sign in to saveAcoelomorpha is a subphylum of very simple and small soft-bodied animals with planula-like features that live in marine or brackish waters. They usually live between grains of sediment, swimming as plankton, or crawling on other organisms, such as algae and corals. Except for two acoel freshwater species, all known acoelomorphs are marine.
Species
acoelomorphs
Subphylum
- PhylumXenacoelomorpha
綱 無腸綱 Acoela 纽皮綱 Nemertodermatida 無腔動物門（學名：Acoelomorpha）是動物界下一個受爭議的門。它們擁有像浮浪幼體的特徵，以往被認為是屬於扁形動物門，但有學者將它們成立為兩側對稱動物下獨自的門[1]。經過miRNA分析結果，若按照親緣分支分類法應分類於後口動物之下[2]。 無腔動物門差不多完全是水生的，棲息在沉積物中，游泳像浮游生物或在藻類上爬行。它們有平衡囊，可以幫助它們平衡。柔軟的身體令學者很難將它們分類。[3] 解剖 無腔動物門非常細小，只長2毫米以下，沒有消化道。[4]消化是由合胞體產生的液泡來包圍吞下的食物。液泡是沒有上皮組織細胞圍堵，不過有時會在口部會有咽連接液泡。所以它們的身體是實心的。 無腔動物門在很多方面都很像扁形動物門，但其構造更為簡單。它們像扁形動物門物種那樣沒有循環系統、呼吸系統或排泄系統。它們沒有真正的腦部或神經節，只在表皮下簡單的神經網絡。這個網絡在前端略為密集。感官器官包括平衡囊，一些會有非常原始的單眼來感應光線。[5] 無腔動物門是雌雄同體的，但沒有性腺，也沒有雌性的繁殖系統。配偶子是由間葉細胞所生產，間葉細胞充滿了它們表皮及消化液泡之間的身體。[5] 參考 ^ Baguñà J, Riutort M. Molecular phylogeny of the Platyhelminthes. Can J Zool. 2004, 82: 168–93. （原始内容存档于2014年12月19日）. ^ Philippe, H. Acoelomorph flatworms are deuterostomes related to Xenoturbella. Nature. 2011, 470: 255–258. ^ Petrov A, Hooge M, Tyler S. Comparative morphology of the bursal nozzles in acoels (Acoela, Acoelomorpha). J. Morphol. May 2006, 267 (5): 634–48. PMID 16485278. doi:10.1002/jmor.10428. ^ The Platyhelminthes and the Acoela. [2009-03-21]. （原始内容存档于2008-05-09）. ^ 5.0 5.1 Barnes, Robert D. Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. 1982: 229. ISBN 0-03-056747-5. 外部連結 Phylogeny of Lower Worms of the Meiofauna Turbellarian t
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Acoelomorpha is a subphylum of very simple and small soft-bodied animals with planula-like features that live in marine or brackish waters. They usually live between grains of sediment, swimming as plankton, or crawling on other organisms, such as algae and corals. Except for two acoel freshwater species, all known acoelomorphs are marine.
== Systematics == === Etymology === The term "acoelomorph" derives from the Ancient Greek words (), the alpha privative, expressing negation or absence, (), meaning "cavity", and (), meaning "form". This refers to the fact that acoelomorphs have a structure lacking a fluid-filled body cavity.