掩喉類
| 掩喉綱 | ||||||||||||
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 From Kunstformen der Natur of Ernst Heckel | ||||||||||||
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掩喉類 (I do not obtain it ask Phylactolaemata) is a group of animals belonging to 外肛動物門 (Bryozoa). It is an animal of the small fixity having a feeler crown and I am common, but am different from other sea mosses at various points including the point that the line of the feeler is not circular, and is horseshoe-shaped by forming a colony. Therefore I summarize this in 掩喉綱 on the classification system and contrapose it against a nude throat rope including all other sea mosses. In addition, in 掩喉類, all is from fresh water whereas nude throats are almost all marine products.
Table of contents
Outside form
It is all a colony-related animal. It is thought that the arborization which branched off is basic in the colony. The branch is slightly flat; is tubular, and the zooid fits into the tip of the branch, and show the former half of the body from the tip when have begun to lengthen, and lose the eyesight of the whole body when shrink.
There is a feeler crown on the tip of the zooid. When the feeler crown becomes the mature form in a part, the thing that a feeler crown becomes approximately circular is known, but is a characteristic horseshoe shape. There is a branch extending to the ventral side parallel to right and left, and I do a U-shape, and feelers line up in the whole along the relationship. Such a form is similar to a broom insect (broom insect animal) than general sea mosses. There is the mouth between the feeler row of this U-shaped bottom, and there is the anus outside of a feeler line of the bottom where similarly is U-shaped. The ventral side by the mouth has the upheaval called the epiglottis, and, as for this, it is with the distinction point with nude throats. There is the viewpoint that this structure comes from the metamere before the mouth. In addition, there is the name of cover mouths because a mouth hides by this structure.
In addition, as for the number or the size of the feeler, categorical; is characterized, but is told that a change is really big by environment.
Form of the colony
The colony is thought to be arborization like the said article basically, but a thing of various form is really found. The thing which attracted zooids thickly without a branch lengthening too much becomes lump-formed or spongy. Such a difference depends on the difference in kind, but it is known that it is different appearance depending on a condition even if similar and makes identification difficult.
There is the kind to secrete quality of agar outside of a colony. It is the figure that the whole colony is carried on a lump of the quality of agar in the agar sea mosses, and it is into a lump form, and quality of agar itself floats in particular in the Oma Rico hairy caterpillars more.
Internal structure
There is large body cavity in the body, and this is related by that of all individuals of the colony. The digestive system beginning in the entrance draws a U-shape as a whole. It is a long bag-formed stomach cul-de-sac in the body, and the part continuing from a mouth continues to anus through the bowels straight briefly. The body wall has string-formed structure to be said to be a funiculus (いちょ funiculus) from a stomach cul-de-sac, but this is connected on the inside peritoneum of the body wall. The peritoneum covers up the backside of the body wall, and the peritoneum of all individuals in the colony is connected again because the partition between the zooid is incomplete. As for the ovary, the testis is prepared into the peritoneums such as a partition or the funiculus on the peritoneum under the surface of a body of the body first half. In addition, a rest bud is formed of a funiculus.
Reproduction and outbreak
The fertilization is carried out with the ovary in the body cavity under the body wall by the zoogamy, and the larva hatches in the state that outbreak advanced to in the body. I have cilia toward a surface of a body with an oval, and the larva which hatched colonizes on the substrate after having floated to some extent, but two bodies zooids more than it are formed in the body at the stage of the floating larva. Therefore I may assume that the outbreak of this animal advances in the body of the parent developing in the womb. After fusing, I increase zooids by budding, and a colony grows up.
Agamogenesis is really carried out well. As described above, the colony grows up by the budding of the zooid, but 断列 is to do it, and this colony often increases the numbers. It is the existence of the rest bud to be important one more.
Rest bud
This kind endures bad conditions such as drying or the chilliness in the form of the rest bud (きゅうが statoblast). This structure is an original thing for this friend. In addition, I am made much for the classifications of the kind in the form every kind because a difference is big and is stable as a form and essence. Therefore, I say when I collect rest buds floating in spring even if I know the kind composition of this kind that inhabited at the area of the sea in last year.
There is a husk of the chitin of two pieces of the right side and the wrong side with a flat thing of the form such as ovals from a circle, and cell group forming the nutritious food such as the egg yolk and a new individual in that is included in the rest bud. A zooid is formed in that when it becomes the suitable condition to begin dormancy once after having experienced drying or low temperature and comes to open the husk of two leaves and causes the new colony.
The rest bud has a floating-related thing and an adherent thing, and chambers containing the air line up around a husk with the floating-related thing and call this with a float. There is not a float with the thing of the adhesion family name, and the part equal to it constitutes a relationship film and thereby attaches to other things. There is the thing displaying ancyroid projections in the edge, and it is thought that I help adhesion among them. In addition, フレデリケラ is adherent, and ヒメテンコケムシ makes only a floating-related thing, but splash sea mosses make a bud on a double holiday. The rest bud is formed of the body of the zooid, the peritoneum of the funiculus, but, as for the floating-related thing, it is formed to the adherent thing in the area that a body wall is accompanied by at the middle.
This rest bud attaches to the feet of the waterfowl and seems to have possibilities to be carried in the distance. Therefore a thing with a wide distribution level is seen in this kind.
There is a thing forming winter bud (hibernacula) in a part with the sea mosses except this. After all this is like the durable resting bud, but both the outbreak and the structure are different from the rest bud. The winter bud occurs on the outside side of the zooid and does an oval. This is regarded as a thing by the transformation of a kind of zooid.
Life cycle
Many things spend winter at a rest bud and when it is spring, it germinates and forms a colony. This lives until autumn and perishes leaving a rest bud when it is winter. But there is the example which germinates like Hinako hairy caterpillar in autumn, and makes a colony in winter.
Activity
In sessile animals, I increase a feeler and have bait and only go down when stimulated. I give up a feeler and do not need to move it. However, a thing with locomotiveness is known to a part. Because locomotiveness is high, the Ayumi sea moss is known, and the name depends in particular on it, too. It is around 5cm a day, though. This kind of colony becomes the structure that the undersurface is easy to move with a string type.
In addition, the small colony of ヒメテンコケムシ and the agar sea moss moves as it, too. The organization does not understand this.
including the biotope
If it is fresh water, I am seen in various environment, and there is a thing seen from the mountain stream to the still water area that is eutrophy. There is the thing which is seen in the imminent water environment such as a rice field or the reservoir, but appears in the place that is not seen by recent environmental degradation. I appoint agar sea moss and ヒメテンコケムシ in Ayumi sea mosses in rare species (R) in endangered species (E) in Red Data Book, invertebrate (1991).
By the way, though I do not find a too special condition in this way, as for the breeding of this kind, it is not easy too much, and it seems to be difficult to breed it for a long time. This makes checking environmental variation difficult and seems to complicate the solution to categorical problems.
In addition, a freshwater sea moss does not belong to all this kind because the thing of nude throats including チャミドロコケムシ exists for freshwater sea mosses although being few. In addition, it is known that ブッデンブロッキア of the soft sporozoan is parasitic on this kind, and there is a report in Japan.
Distribution
I am known from all parts of the world. ヤハズハネコケムシ is common in Japan, but has global distribution. The Ayumi sea moss is from the Tohoku district and to the north mainly in Japan and is distributed over the northern part of North America and the chilly environment widely worldwide from Europe. On the other hand, the agar sea moss is from Kansai and to the south in Japan and is a kind of south distributed over Indonesia from Taiwan origin worldwide. In addition, there is the thing with Japan and narrow distribution level only in the Korean Peninsula like Hinako hairy caterpillar.
In addition, the kind of a southern system and the northern system mingles in this way in Japan, and globally this kind is a rich area.
Interest
There is not the thing useful directly. Because it was a person of cilia viscous liquid eating, it might be useful for quality of the water purification, but has not attracted attention of the work.
害をなすものとしては、ヒメテンコケムシが養魚場で害をなすことが知られる。この種の体腔液に毒成分が含まれるので、養魚場内を網でかき回した際に、この動物の群体が壊れ、その結果魚が死ぬことがある。同様の毒素はカンテンコケムシも持っているという。毒の性質等についてはよく分かっていないらしい。
また、カンテンコケムシの群体は大きくなるので、養魚場の網や工場の取水口に発生して水を詰まらせる場合もある。さらに帰化動物のオオマリコケムシは数十cmにもなる群体を作り、同様の被害を与えるほかに、見かけでも気味悪がられる。
系統の問題
この類は基本的な体制などにおいては他のコケムシ類との共通性が高いが、他方で馬蹄形の触手冠、個虫間で仕切られていない体腔など、かなり重要な違いと見られるものもある。そのため、これが他のコケムシ類とは別の系統であるとの説がある。それによると、体制の共通性はむしろ触手を持って群体で固着生活をすることによる収斂と見るべきだと言う。発生の様子もこの類が直接発生的なのに対して裸喉類がトロコフォア様の幼生を出す点も大いに異なるが、これは海産動物から派生した淡水産の種には往々に見られることである。触手冠の形態などからホウキムシ類との類縁を主張する説もあり、分子遺伝学からももこれを支持する結果が報告されているらしい。したがって、単系統をなさないにしても、それほど遠縁ではないのかもしれない。
分類
現生種は約50種で、すべてを単一の掩喉目にまとめ、その下に数科をおく。体系には若干の揺れがあるようである。日本からは15種ほどが知られる。主なものを下に示す。
暗喉目
- ハネコケムシ科：フレデリケラ Fredericella、ヒナコケムシ Stephanella、ハネコケムシ Plumatella、トウアンコケムシ Gelatinella、ヒアリネラ Hyalinella
- ヒメテンコケムシ科：ヒメテンコケムシ Lophopodella、カンテンコケムシ Asajirella
- アユミコケムシ科：アユミコケムシ Cristatella
参考文献
- 上野益三,『日本淡水生物学』,1973,図鑑の北隆館
- 岡田要,『新日本動物図鑑』,1976,図鑑の北隆館
- 白山義久編集；岩槻邦男・馬渡峻輔監修『無脊椎動物の多様性と系統』(2000)裳華房
This article is taken from the Japanese Wikipedia 掩喉類
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