関: nauplii

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/02/15 22:03:32」(JST)

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エビのノープリウス幼生

ノープリウス（Nauplius、ノープリウス幼生）は甲殻類に共通の最も初期の幼生の名である。ノウプリウス、あるいはナウプリウスと表記される場合もある。

概要

ノープリウスは、甲殻類の最も基本的な幼生の姿である。体はまだ頭部、胸部、腹部にわかれていない^[1]。多くの甲殻類はゾエア(広義)の時期に進む。

分類群によってその外見はやや異なるが、三対の機能的な頭部付属肢をもっている。体は楕円形や棍棒状等さまざまであるが、前方にまず枝分かれのない第一触角、その次に二枝型の第二触角、体中央より後ろの側面にもう一対の付属肢があり、これは大顎である。これより後方の付属肢は欠如しているか原基状である^[1]。また、はっきりした体節は見られない。この形は、甲殻類の成体で言えば頭部の前半分に当たる。成体の頭部では、この後ろに小顎が二対あり、それに続いて胸部の体節が並んでいる。

ノープリウス眼

体の前端中央(正中線上)に一個の単眼がある。側眼と対比して中央眼と呼ばれるもののひとつである。この眼をノープリウス眼(Naupliar eye)という。3個のレンズとX字型をした黒や赤などの色素をもち、簡単な明暗視器の構造をしている^[2]。また、多くの群では変態に際して退化消失し、側眼である一対の複眼を発達させるが、ケンミジンコ・カイミジンコなどは成体にまで残り、ノープリウス眼のみで一生を過ごす^[2]。

メタノープリウス

この姿から、発生が進むにしたがって次第に体節と付属肢を増加させる。ノープリウス幼生の体の後半に付属肢のもと（原基）が形成される、ノープリウスの後期に当る段階をメタノープリウス (Metanauplius) という。頭部に第一小顎と第二小顎が加わる。顎脚綱ヒゲエビ類、軟甲綱オキアミ類の一部はメタノープリウスの時期に孵化する。それ以降はそれぞれの分類群によって独特の経過を経て発生が進む。

卵ノープリウス

派生的である十脚目抱卵亜目では、ノープリウスより多くの付属肢を持つ状態の幼生が最初に現れる。それらの群は、より発生が進んだ状態(ゾエア期)に孵化するものと考えられる。つまり、ノープリウス幼生の時期を卵の中で過ごしてしまうのである。そのような群でも、卵内の発生を見れば、必ず二対の触角と大顎の原基だけが見られる時期があり、これを卵ノープリウス (egg nauplius) とよぶ^[3]。この卵は直径500μm以上の大型で多量の卵黄を含むため、ノープリウスは卵表面に浮き彫りに姿を現すのみである^[4]。

観察

ノープリウス幼生を見るための最も簡単な方法は、ブラインシュリンプ、あるいはシーモンキーを飼育することである。これらはいずれも甲殻綱鰓脚亜綱無甲目に属するアルテミア　Artemia のことであるが、飼育魚の餌用あるいは愛玩用として市販されている。乾燥状態の卵を適度な塩水に入れれば、一晩で孵化して赤っぽい色の幼生が多数遊泳するのが見られる。この幼生がノープリウスである。

幼生をよく見れば、小さな腕を動かして泳いでいることが分かる。顕微鏡で観察すれば、先端が幅広い体に二対の腕が伸びており、それらの真ん中に一つだけの眼があることが観察できる。二対の腕のうちの前方のものは第一触角で、単独の棒状、二番目が第二触角で、中途で二分している。また、体の中ほどにはもう一対の付属肢があるが、これは大顎である。

飼育を続ければ、幼生の体は次第に長くなり、大顎の後方に次第に新たな付属肢が形成されて行く。

出典

^ ^a ^b 『岩波生物学辞典』p.1068b「ノープリウス」
^ ^a ^b 『岩波生物学辞典』p.1068c「ノープリウス眼」
^ 岡田(1965)p.435
^ 『岩波生物学辞典』p.1149a「卵ノープリウス」

参考文献

岩槻邦男・馬渡峻輔監修；石川良輔編集、『節足動物の多様性と系統』,(2008),バイオディバーシティ・シリーズ7(裳華房)
岡田要、『新日本動物図鑑〔中〕』、(1965)、図鑑の北隆館
巌佐庸・倉谷滋・斎藤成也・塚谷裕一編『岩波生物学辞典』岩波書店、2013年、第5版。ISBN 4-00-080314-X。

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English Journal

A method for stable gene knock-down by RNA interference in larvae of the salmon louse (Lepeophtheirus salmonis).

Eichner C1, Nilsen F2, Grotmol S2, Dalvin ST3.Author information 1SLCR-Sea Lice Research Center, Department of Biology, University of Bergen, Thormøhlensgt. 55, 5008 Bergen, Norway. Electronic address: christiane.eichner@bio.uib.no.2SLCR-Sea Lice Research Center, Department of Biology, University of Bergen, Thormøhlensgt. 55, 5008 Bergen, Norway.3SLCR-Sea Lice Research Center, Institute of Marine Research, 5817 Bergen, Norway.AbstractThe salmon louse (Lepeophtheirus salmonis), an ectoparasitic copepod of salmonid fish, is a major threat to aquaculture in Norway, Ireland, Scotland and Canada. Due to rise in resistance against existing pesticides, development of novel drugs or vaccines is necessary. Posttranscriptional gene silencing by RNA interference (RNAi), when established in a high throughput system is a potential method for evaluation of molecular targets for new medical compounds or vaccine antigens. Successful use of RNAi has been reported in several stages of salmon lice. However, when we employed a previously described protocol for planktonic stages, no reproducible down-regulation of target genes was gained. In the present study, we describe a robust method for RNAi, where nauplius larvae are soaked in seawater added double stranded RNA (dsRNA). In order to test for when dsRNA may be introduced, and for the efficacy and duration of RNAi, we performed a series of experiments on accurately age determined larvae, ranging from the hatching egg to the copepodid with a salmon louse coatomer and a putative prostaglandin E synthase gene. Presumptive knock-down was monitored by real time PCR. Significant gene silencing was obtained only when nauplius I larvae were exposed to dsRNA during the period in which they molted to nauplius II. A knock down effect could be detected 2days after soaking, and it remained stable until the last measurement, on day 12. Soaking nauplius I larvae, knock-down was verified for six additional genes with a putative role in molting. For one chitinase, a loss-of-function phenotype with abnormal swimming was obtained. Hence, RNAi, induced in the nauplius, may facilitate studies of the molecular biology of the louse, such as the function of specific genes in developmental processes and physiology, host recognition, host-parasite interaction, and, in extension, the engineering of novel medicines.
Experimental parasitology.Exp Parasitol.2014 Mar 14. pii: S0014-4894(14)00048-4. doi: 10.1016/j.exppara.2014.03.014. [Epub ahead of print]
The salmon louse (Lepeophtheirus salmonis), an ectoparasitic copepod of salmonid fish, is a major threat to aquaculture in Norway, Ireland, Scotland and Canada. Due to rise in resistance against existing pesticides, development of novel drugs or vaccines is necessary. Posttranscriptional gene silenc
PMID 24632188

Larval vision contributes to gregarious settlement in barnacles: adult red fluorescence as a possible visual signal.

Matsumura K1, Qian PY.Author information 1KAUST Global Collaborative Research Program, Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong.AbstractGregarious settlement, an essential behavior for many barnacle species that can only reproduce by mating with a nearby barnacle, has long been thought to rely on larval ability to recognize chemical signals from conspecifics during settlement. However, the cyprid, the settlement stage larva in barnacles, has one pair of compound eyes that appear only at the late nauplius VI and cyprid stages, but the function(s) of these eyes remains unknown. Here we show that cyprids of the intertidal barnacle Balanus (=Amphibalanus) amphitrite can locate adult barnacles even in the absence of chemical cues, and prefer to settle around them probably via larval sense of vision. We also show that the cyprids can discriminate color and preferred to settle on red surfaces. Moreover, we found that shells of adult B. amphitrite emit red auto-fluorescence and the adult extracts with the fluorescence as a visual signal attracted cyprid larvae to settle around it. We propose that the perception of specific visual signals can be involved in behavior of zooplankton including marine invertebrate larvae, and that barnacle auto-fluorescence may be a specific signal involved in gregarious larval settlement.
The Journal of experimental biology.J Exp Biol.2014 Mar 1;217(Pt 5):743-50. doi: 10.1242/jeb.096990.
Gregarious settlement, an essential behavior for many barnacle species that can only reproduce by mating with a nearby barnacle, has long been thought to rely on larval ability to recognize chemical signals from conspecifics during settlement. However, the cyprid, the settlement stage larva in barna
PMID 24574388

Transcriptome analysis of the couch potato (CPO) protein reveals an expression pattern associated with early development in the salmon louse Caligus rogercresseyi.

Gallardo-Escárate C1, Valenzuela-Muñoz V2, Nuñez-Acuña G2, Chávez-Mardones J2, Maldonado-Aguayo W2.Author information 1Laboratory of Biotechnology and Aquatic Genomics, Interdisciplinary Center for Aquaculture Research (INCAR), University of Concepción, P. O. Box 160-C, Concepción, Chile. Electronic address: crisgallardo@udec.cl.2Laboratory of Biotechnology and Aquatic Genomics, Interdisciplinary Center for Aquaculture Research (INCAR), University of Concepción, P. O. Box 160-C, Concepción, Chile.AbstractThe couch potato (CPO) protein is a key biomolecule involved in regulating diapause through the RNA-binding process of the peripheral and central nervous systems in insects and also recently discovered in a few crustacean species. As such, ectoparasitic copepods are interesting model species that have no evidence of developmental arrest. The present study is the first to report on the cloning of a putative CPO gene from the salmon louse Caligus rogercresseyi (CrCPO), as identified by high-throughput transcriptome sequencing. In addition, the transcription expression in larvae and adults was evaluated using quantitative real-time PCR. The CrCPO cDNA sequence showed 3261 base pairs (bp), consisting of 713bp of 5' UTR, 1741bp of 3' UTR, and an open reading frame of 807bp encoding for 268 amino acids. The highly conserved RNA binding regions RNP2 (LFVSGL) and RNP1 (SPVGFVTF), as well the dimerization site (LEF), were also found. Furthermore, eight single nucleotide polymorphisms located in the untranslated regions and one located in the coding region were detected. Gene transcription analysis revealed that CrCPO has ubiquitous expression across larval stages and in adult individuals, with the highest expression from nauplius to copepodid stages. The present study suggests a putative biological function of CrCPO associated with the development of the nervous system in salmon lice and contributes molecular evidence for candidate genes related to host-parasite interactions.
Gene.Gene.2014 Feb 15;536(1):1-8. doi: 10.1016/j.gene.2013.11.100. Epub 2013 Dec 14.
The couch potato (CPO) protein is a key biomolecule involved in regulating diapause through the RNA-binding process of the peripheral and central nervous systems in insects and also recently discovered in a few crustacean species. As such, ectoparasitic copepods are interesting model species that ha
PMID 24342663