透明薄皮蚤

**薄皮蚤屬**（學名：_Leptodora_）為薄皮蚤科動物唯一的一個屬。過往本屬只有透明薄皮蚤（學名：_Leptodora kindtii_）一個物種，直至 2009 年本屬的第二個物種被發現。這兩個物種在對比其他雙甲下綱物種來說比較大，近乎透明及透光，是一類捕食性物種。本屬物種最長可長至 21 mm（0.83 英寸），有兩枝可用，作游泳的觸角，以及一隻複眼。腿可用作捕捉碰巧路過的橈足亞綱物種。

透明薄皮蚤見於北半球溫帶的湖泊中，很可能是枝角目物種當中唯一曾被報章報導過的已描述生物；而 _L. richardi_ 現時只見於俄羅斯遠東地區的黑龍江流域，儘管日本認為在其國內分佈的物種亦是 _L. richardi_。
For most of the year, _Leptodora_ reproduces 單性生殖，with males only appearing late in the season, to produce winter eggs which hatch the following spring. _Leptodora_ is the only genus in its family, the **Leptodoridae**, and suborder, **Haplopoda**.

## 形態描述

薄皮蚤屬物種的成體是北美洲原生浮游枝角目物種當中體型最大的；至於到底有多大，各種報告間不盡相同，但雌性成體普遍可長至 12 mm（0.47 英寸）長，部分報告聲稱可長至 21 mm（0.83 英寸）長。這些動物的身體約有 98% 是透明的，以避免被魚類獵食。

Lilljeborg notes:  

> Das Weibchen ist in so hohem Grade durchsichtig, in wahrem Sinne »wasserhell», dass oft nur die Bewegungen ihr Dasein in dem Wasser verrathen. Bei auffallendem Sonnenlicht wird gewöhnlich der Schatten früher als das Thier selbst entdeckt.
> 
> 

> The female is transparent to such a high degree, literally "as clear as water", that her presence is often only given away by her movements. In bright sunlight, the shadow is normally seen before the animal itself.
> 
> 

The male is similarly transparent. The abdomen is elongated, but the carapace is small and only covers the brood pouch.

胸節的六對附肢形成一個「餵哺籃」，用以捕捉獵物。
The second 觸角 are used for swimming, while the first antennae are 痕跡器官 in females but elongated in males, where they are used in 有性生殖. There is a single large 複眼 which takes up much of the animal's head. It comprises around 500 facets, which are spherically arranged, and the whole eye is movable by up to 10° in any direction.

## 分佈

透明薄皮蚤廣泛分佈於北半球溫帶的湖泊中，見於北美洲、亞洲、歐洲及非洲。在北美洲，其分佈範圍南至德克薩斯州及俄克拉荷馬州；在中國大陸分佈於浙江、江蘇、安徽、江西、湖北、吉林、黑龍江、雲南、內蒙古等地，主要棲息於大中型湖泊的敞水區、也出現在沿岸以及小型湖泊與積水較深的池塘中。在歐洲、北非部分地區、阿拉伯半島北部及亞洲喜馬拉雅山脈以北地區亦有分佈。

## 生態及行為

透明薄皮蚤是一種貪婪的捕食者，能夠控制其偏愛獵物的數量，一般都是溞屬（_Daphnia_）、_Bosmina_, _Ceriodaphnia_, _Diaphanosoma_, _Diaptomus_, _Polyphemus_ 及劍水蚤屬（_Cyclops_）等各屬物種的幼體。 It seems to encounter its prey by chance, with contact initiating a 反射 (生理學), in which the 腹 is brought forward to close the feeding basket. In many cases, the prey escapes this haphazard response. Juvenile _Daphnia_ are slower than adults to respond to the predator's attack, and are therefore more likely to be caught.

The most important predators of _Leptodora_ are fishes, including 白鮭屬，perch, ziege and 歐白魚.

In 琵琶湖，日本， _L. kindtii_ is 寄生 by the 線蟲動物門 _Raphidascaris biwakoensis_, a parasite of 魚.

## 生命週期

雌性薄皮蚤屬動物能夠僅僅透過單性生殖就可以產卵，而且每隔 12 小時就又可以再下一窩卵子。這些卵子孵化後進入幼體階段，身長約 2 公釐（0.079 英寸）。之後牠們在長為成蟲之前，還要再經歷六個 instar，到了完全成長，體長增至 6 公釐（0.24 英寸）。而事實上，從孵化到成蟲階段，需時只要 3 到 6 天，視乎孵化時的環境溫度。在一年的絕大多數時候，薄皮蚤屬動物的繁殖都只靠單性生殖，所生產的卵皆為雌性，並沒有雄性的卵子 。到了秋季，透過單性生殖的雄性卵子開始出現；雄性與雌性進行有性生殖才變得可行。這些透過交配行為誕下的受精卵會在牠們越冬的所在地沉到最底，直到下一年才會孵化，成為 nauplius-like larvae.。

## Related taxa

_Leptodora_ is so distinct from other cladocerans that some authors have suggested grouping all other cladocerans into a 演化支 called "Eucladocera", with _Leptodora_ as its 姐妹群. It is now believed, however, that _Leptodora_ is sister to Onychopoda, being the only genus in the family **Leptodoridae** and the subclass **Haplopoda**. Features which separate it from other families include its large size, the lack of branchial appendages (鰓 s) on its legs, the reduction of the carapace, and the fact that the winter eggs hatch as nauplii.

## Taxonomic history

_Leptodora kindtii_ is "probably the only cladoceran ever described in a newspaper". The German microscopist Gustav Woldemar Focke organised a 學術研討會 in 不萊梅 in 1844 together with the pharmacist Georg Christian Kindt. He studied the fauna of the ditches surrounding the city (the _Bremer Stadtgraben_) and displayed live specimens at the meeting. During the meeting, he also published a description of the species in the _Weser-Zeitung_ on Sunday September 22, 1844, placing the species in the genus _Polyphemus_. However, this description was ignored by the scientific community, and Wilhelm Lilljeborg described the species in 1861 with the name _Leptodora hyalina_. The 異名 was not noticed until Simon Albrecht Poppe informed Lilljeborg of it in 1889, and Lilljeborg corrected the error in his 1900 專著.

2009 年，Korovchinsky 首度為本屬的第二個物種 _Leptodora richardii_ 作出描述：這個物種採樣自黑龍江盆地的湖泊，包括博隆湖。

### 異名

現時下列組合均被視為透明薄皮蚤（_Leptodora kindtii_）的異名：

* _Polyphemus kindti_ Focke, 1844
* _Hyalosoma dux_ Wagner, 1868
* _Leptodora angusta_ Sars, 1890
* _Leptodora hyalina_ Lilljeborg, 1861
* _Leptodora pellucida_ Joseph, 1882

### 語源

The name _Leptodora_ is from the 希臘語 words _leptos_ and _dora_, collectively meaning thin-skinned. The 種加詞 _kindtii_ is presumed to refer to G. C. Kindt, who worked closely with Focke. The alternative spelling _kindti_ is sometimes encountered, but is no longer considered correct under the 國際動物命名法規. The epithet _hyalina_, used by Lilljeborg, is from the Greek _ὕαλος_, and means glassy.

## 下屬物種

本屬包括以下物種：

* _Leptodora kindti_ (Focke, 1844)
* _Leptodora richardi_ Korovchinsky, 2009

## 參考文獻

## 外部連結

* _Leptodora kindtii_. Missouri State University. 2006-08 [2022-01-20]. （原始內容存檔於 2012-03-04） （英語）.
* Creature of the Month: _Leptodora kindtii_. Zooplankton-online.net. 2005-07 [2010-03-19]. （原始內容存檔於 2006-10-19） （英語）.
* _Leptodora kindtii_ swimming (QuickTime). University of New Hampshire. 2020-02 （英語）.
* _Leptodora kindtii_ swimming and bending. University of New Hampshire. [2010-03-19]. （原始內容 (QuickTime) 存檔於 2006-09-05） （英語）.