Identification of tardigrade species is still reliant mostly on morphological and morphometric traits. Given that the number of taxonomically significant traits available in the genus Milnesium is exceptionally low, ontogenetic variability may provide additional methods for species delineation. However, it is notoriously difficult to establish whether both immature and sexually mature instars are present in examined populations. Here, we developed a simple analytical morphometric method that helps in testing whether both immature and mature life stages are present in a given set of individuals. In order to achieve this, we analysed 21 populations representing 11 Milnesium species, with developmental tracking data available for four species. Using cluster analysis, individuals were assigned accurately to three groups of instars: hatchlings, juveniles and adults (third instar onwards). Our analyses revealed that the most useful character in life-stage classification is buccal tube length. The method of classification of instars presented herein could be used as a simple tool for identification of the number of life stages present in a population. Finally, using our algorithm, we analysed morphometric datasets underlying the descriptions and redescriptions of all known Milnesium species to date and concluded that the majority of them did not include all three life-stage groups.

中文翻译：

---

无法使用遗传跟踪时该怎么办：形态学方法来对米尔尼斯（Tardigrada）中的幼虫进行分类

缓坡物种的鉴定仍然主要依赖于形态和形态特征。鉴于Milnesium属中可用的具有分类学意义的重要性状数量极少，因此个体遗传变异性可能为物种划分提供其他方法。但是，要确定受检人群中是否同时存在未成熟和性成熟的幼虫是非常困难的。在这里，我们开发了一种简单的分析形态计量学方法，可帮助测试给定的一组个体中是否存在未成熟和成熟的生命阶段。为了实现这一目标，我们分析了代表11镁的21个种群物种，并提供四个物种的发育追踪数据。使用聚类分析，将个体准确地分为三龄幼虫：孵化，幼体和成年幼虫（第三龄以上）。我们的分析表明，生命阶段分类中最有用的特征是颊管长度。本文介绍的龄期分类方法可以用作鉴定种群中生命阶段数量的简单工具。最后，使用我们的算法，我们分析了迄今为止所有已知的米尔尼斯物种的描述和重新描述所基于的形态计量数据集，并得出结论，其中大多数不包括所有三个生命阶段组。