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Segmentation and limb formation during naupliar development of Tigriopus californicus (Copepoda, Harpacticoida).
Arthropod Structure & Development ( IF 2 ) Pub Date : 2019-04-12 , DOI: 10.1016/j.asd.2019.04.001
Hendrikje Hein 1 , Sandra Smyth 1 , Ximena Altamirano 1 , Gerhard Scholtz 1
Affiliation  

Naupliar development in copepods includes the generation of usually five pairs of post-mandibular segments. Since copepod nauplii show no outer body articulation, the only indication of larval segmentation is the expression of limb buds. Yet, in copepods the timing and sequence of limb bud expression in larval development varies to a large degree. In harpacticoid nauplii for instance, the 1st maxillae are formed at an early naupliar stage. By contrast, the four remaining pairs of limb buds frequently appear simultaneously with the last naupliar stage. The complete process of larval segment formation takes place under the body surface and has never been described in detail. To broaden our knowledge of early segmentation in copepods, we here describe the segmentation of the harpacticoid nauplius Tigriopus californicus by analysing the expression of the segment marker Engrailed and uncover the sequential addition of seven post-mandibular segments. The stripe formation and arrangement of labelled cells corresponds largely to those of other crustaceans studied in this respect. Together with a morphological approach using histology, SEM, and 3D-reconstructions based on CLSM we solve the so far controversial identity of the external limb buds in the final naupliar stage. In contrast to previous studies, we can show that all limb pairs from the 1st maxillae to the 3rd thoracopods are formed. Yet, the anlage of the maxilliped (1st thoracopod) remains hidden underneath the cuticle being never externally expressed in the nauplius.

中文翻译:

加利福尼亚虎(Tipriopus californicus)(Copepoda,Harpacticoida)无节幼体发育过程中的节段和肢体形成。

co足类的幼稚发育包括通常产生五对下颌后节。由于co足类无节幼体没有显示出外体关节,因此幼虫节段的唯一迹象是肢芽的表达。然而,在足足动物中,幼虫发育中肢芽表达的时间和顺序有很大的不同。例如,在类类拟幼体无节幼体中,第一上颌骨形成于无节幼体的早期。相比之下,剩下的四对肢芽经常在最后的幼体阶段同时出现。幼虫节段形成的完整过程发生在体表下,至今没有详细描述。为了拓宽我们对co足类动物早期细分的知识,我们在这里通过分析分段标记Engrailed的表达并揭示下颌后七个分段的相继添加来描述类拟南浦无节幼体Tigriopus californicus的分段。标记细胞的条纹形成和排列在很大程度上与在此方面研究的其他甲壳类的条纹形成和排列相对应。结合使用基于CLSM的组织学,SEM和3D重建的形态学方法,我们解决了迄今为止在无节幼体阶段外肢芽的争议性身份。与以前的研究相比,我们可以显示从第一上颌到第三胸足的所有肢对都已形成。然而,最大的(第一个胸足类动物)的角膜仍然隐藏在角质层的下方,从未在无节幼体中外部表达。
更新日期:2019-11-01
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