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Jaw Worms

Gnathostomulida

Brief Summary

    Gnathostomulid: Brief Summary
    provided by wikipedia

    Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956.

    Gnathostomulida: Brief Summary ( Italian )
    provided by wikipedia Italiano

    Il phylum Gnathostomulida (dal greco: gnathos = mascella; stoma = bocca) è costituito da circa 80 specie di animali vermiformi marini, di piccole dimensioni (0,5 – 3 mm), viventi negli spazi tra le particelle di sabbia e di limo delle spiagge fangose anaerobiche. Gli gnatostomulidi si nutrono di funghi e microrganismi che raschiano dai granelli di sabbia tramite mascelle ben sviluppate di cui è dotata la bocca, la quale è posta nella zona anteriore-ventrale.

    Gnathostomulida: Brief Summary ( Spanish; Castilian )
    provided by wikipedia Español

    Los gnatostomúlidos (Gnathostomulida, del griego gnathos, "mandíbula" y stomula, "diminutivo de boca") son un filo de animales vermiformes, bilaterales, acelomados o pseudocelomados dependiendo de autores, marinos, de pequeño tamaño (0,5 - 3 mm), que viven entre las partículas de la arena y los limos (formando parte de la meiofauna), en ambientes principalmente anaerobios, (lugares en los que se encuentran las mayores densidades de población). Se nutren de hongos y microorganismos que se hallan en los granos de arena con las características mandíbulas de que está dotada su boca, situada en la zona anteroventral. Se conocen casi 100 especies.​

    No existe registro fósil y han pasado inadvertidos mucho tiempo por sus dimensiones mínimas y su fragilidad y transparencia, por lo que hoy hay una gran controversia en lo que respecta a su historia evolutiva y su taxonomía.

    Gnathostomulida: Brief Summary ( French )
    provided by wikipedia Français
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    Les Gnathostomulida sont un embranchement de vers marins interstitiels. Une centaine d'espèces sont connues. Ils sont inclus dans le super-embranchement des Gnathifera avec les Syndermata (Rotifera et Acanthocephala) et les Micrognathozoa, dû à la structure de leurs pièces buccales,,.
    Kiefermündchen: Brief Summary ( German )
    provided by wikipedia Deutsch

    Die Kiefermündchen (Gnathostomulida) sind kleine, ein bis vier Millimeter lange marine Würmer, die zur Meiofauna gezählt werden. Die 91 Arten leben vor allem in Sanden mit hohem Anteil von Sulfiden und organischen Stoffen. Alle Arten sind Zwitter. Die ersten Exemplare wurden 1928 von Adolf Remane entdeckt.

    Namensgebend ist das Kieferpaar am vorderen Ende der Tiere. Das Ektoderm besteht aus monociliären Zellen, d. h. dass jede einzelne Zelle jeweils nur eine Cilie besitzt. Diese monciliären Zellen traten schon bei der "Unterabteilung" der Bilateria auf und sind bei den Gnathostomulida im Gegensatz zu den Plattwürmern (Plathelminthes) noch erhalten geblieben. Mit dem Schlag der Cilien bewegen sie sich sowohl vorwärts wie rückwärts.

    Abgeändert sind die Protonephridien: Hier reihen sich im Körper mehrere Organe. Bei jedem einzelnen Organ besitzt nur noch die Terminalzelle ein Cilium.

    Kiefermündchen sind fossil nicht belegt. Wegen des ähnlichen Kieferapparates und der Protonephridien nimmt man eine Verwandtschaft mit den Rädertierchen (Rotatoria) und den Bauchhärlingen (Gastrotricha) an.

    Гнатостомулиды: Brief Summary ( Russian )
    provided by wikipedia русскую Википедию

    Гнатостомули́ды (лат. Gnathostomulida) — тип беспозвоночных из группы Platyzoa. Обладают микроскопическими размерами (0,5—1 мм, некоторые до 4 мм в длину). Гнатостомулиды живут в заиленном песчаном грунте морских мелководий (обычно до 25 метров, реже до 400 м). Способны переносить дефицит кислорода, а также сероводородное и органическое загрязнение. Описано порядка 100 современных видов. В России — 1 вид. Ископаемые останки гнатостомулид не описаны.

    顎口動物: Brief Summary ( Japanese )
    provided by wikipedia 日本語

    顎口動物(がくこうどうぶつ)は、顎口動物門に属する動物の総称である。体長0.2-3.5mm、円筒状の体は頭部と胴部に区分される。頭部にある口にはクチクラ性の固い顎を持つことが特徴である。この顎で砂の表面の細菌藻類をこそげ落として摂食する。海洋や汽水域の砂中に生息する。非常に生息密度が高い場合も多く、1リットルの砂から6000匹以上が見つかることもある。

    顎口動物は1956年に新しく発見された。当初は扁形動物に属すると考えられていたが、その後の研究結果により、独立した動物門として分類されるようになった。

    他の動物との類縁関係は長い間謎とされており、未だに決定的な見解は得られていない。形態の比較から扁形動物の類縁関係を指摘する説がある一方、器官の類似から輪形動物鉤頭動物と類縁関係にあるという説もある。分子生物学的な研究では線形動物毛顎動物と密接な関係がある示唆されている。

    颚胃动物门: Brief Summary ( Chinese )
    provided by wikipedia 中文维基百科
    악구동물: Brief Summary ( Korean )
    provided by wikipedia 한국어 위키백과

    악구동물(顎口動物, Gnathostomulid, jaw worm)은 악구동물문(Gnathostomulida)에 속하는 무척추 동물이다. 아주 작은 해양성 동물 문(門)으로 몸은 좌우대칭이다. 대부분 0.5 에서 1 mm 정도이다. 편충동물처럼 이들은 섬모성 표피를 지니고 있으나, 독특하게도 세포당 하나의 섬모만을 지니고 있다. 이들은 체강이 없으며, 순환계 또는 호흡기관이 없다. 각각의 악구동물은 자웅동체이며, 하나의 난소(ovary)와 저장낭(testis)을 지니고 있다. 입 속에 단단한 턱(악구)을 지니고 있고, 산소가 필요없는 해저 바닥에서 모래에 붙어있는 작은 생물들을 긁어 먹는 분류학상의 특징을 가지고 있다. 복잡한 형태의 각피성 입 부분을 가진 좌우대칭적인 인두는 이들이 윤형동물과 밀접한 관련이 있음을 보여주고 있으며, 다른 동물문과 함께 유악동물군을 형성한다. 약 100여 종이 발견되고 있으며, 아직 상당수 종이 미기록되어 있을 것으로 추측된다. 알려진 종들은 2개의 목으로 분류되고 있다. 필리스페르모이데아목(Filospermoidea) 동물은 매우 길고, 주둥이 모양의 돌기가 길게 늘어나는 특징이 있다. 부르소바기노이데아목(Bursovaginoidea) 동물은 한쌍의 감각 기관이 있고, 하나의 수 생식기를 지닌 특징을 보여주며, bursa라고 불리는 정충(sperm)을 저장하는 기관을 가지고 있다.

    악구동물 중에서 화석은 발견되고 있지 않다.

Comprehensive Description

Distribution

    Distribution
    provided by EOL staff

    Gnathostomulids are found worldwide.

Morphology

    Morphology
    provided by EOL staff

    The elongate body of a gnathostomulid, which is typically less than 2 mm long (range 0.3 to 3.5 mm), usually has distinct head, trunk, and tail regions. Outer epithelial cells each have single cilia which collectively help the animal glide between sand grains. The ventral mouth leads to a blind gut (i.e., the gut has just a single opening, rather than a separate mouth and anus), but undigested solid waste may leave not only through the mouth but also via a temporary anus or temporary dorsal connection to the epidermis.

    (Brusca and Brusca 2003; Sørensen and Sterrer 2009 and references therein; Margulis and Chapman 2010)

Habitat

    Habitat
    provided by EOL staff

    Gnathostomulids are found mainly in medium or fine-grained sand mixed with detritus and are often very common in sand from seagrass beds. They may occur at high densities in anoxic, sulfide-rich conditions (population densities of more than 6000 individuals per liter of sediment have been reported). They occur from the intertidal zone to depths of hundreds of meters.

    (Brusca and Brusca 2003; Sørensen and Sterrer 2009 and references therein; Margulis and Chapman 2010)

Reproduction

    Reproduction
    provided by EOL staff

    Gnathostomulids are hermaphrodites, either simultaneously functioning as male and female or as male first. One egg matures at a time and fertilization is apparently internal; in at least some species, sperm are apparently injected by an individual beneath the skin of its mate. Fertilized eggs are believed to be deposited singly. Development is direct, with no larval stage.

    (Brusca and Brusca 2003; Sørensen and Sterrer 2009 and references therein; Margulis and Chapman 2010)

Evolution

    Systematics and Taxonomy
    provided by EOL staff

    There are close to 100 described gnathostomulid species, but many more times that number likely await discovery. Gnathostomulids were first described, in 1956, as turbellarian Platyhelminthes (free-living flatworms), but were given phylum rank in 1969. Recent work has supported the recognition of a monophyletic clade Gnathifera consisting of the clade Syndermata (Rotifera + Acanthocephala) plus the Gnathostomulida (Witek et al. 2009 and references therein). Sørensen et al. (2006) investigated relationships within the Gnathostomulida.

    (Brusca and Brusca 2003; Sørensen and Sterrer 2009 and references therein; Margulis and Chapman 2010)