Species of the genus Euphausia dominate the euphausiid biomass of the Southern Ocean, the three largest being Euphausia superba, E. triacantha and E. crystallorophias. We measured a number of morphological features to identify differences between, and within, these species to obtain ecological insights. Interspecifically, the greatest difference was carapace size, with that of E. superba being by far the largest and most variable. This likely reflects its prolific spawning capacity compared with other euphausiid species. E. triacantha exhibited an extended sixth abdominal segment that could facilitate greater levels of thrust in the tail flip escape response. The pleopods, which provide propulsion in forward swimming, were more than 50% larger in E. superba, indicating a greater capacity for directional movement at high velocities. E. crystallorophias had eyes that were almost double the size of those in E. superba and E. triacantha, which may help retain visual resolution within its under-ice habitat. Intraspecifically, we found the above morphological features differed little between sexes and developmental stages in E. crystallorophias and E. triacantha, but differed significantly in E. superba. Compared to females and juveniles, male E. superba had significantly larger eyes and pleopods, whilst the carapace in males became shorter as a proportion of body length during growth. These features indicate a greater capacity for searching and swimming in males, which, we hypothesise, increases their ability to locate and fertilise females. This morphological specialisation in male E. superba is indicative of comparatively greater inter-male competition resulting from its tendency to form large, dense swarms.

中文翻译：

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南大洋磷虾属物种的比较形态学：两性二态特征的生态学意义

磷虾属的物种在南大洋的磷虾生物量中占主导地位，其中三个最大的是 Euphausia superba、E. triacantha 和 E.crystallorophias。我们测量了许多形态特征，以确定这些物种之间和内部的差异，以获得生态见解。种间差异最大的是甲壳尺寸，E. superba 的甲壳尺寸是迄今为止最大和变化最大的。这可能反映了其与其他磷虾类物种相比的多产产卵能力。E. triacantha 表现出延长的第六个腹部节，这可以促进尾部翻转逃逸反应中更大程度的推力。在向前游泳时提供推进力的腹足在 E. superba 中大 50% 以上，表明在高速下定向运动的能力更大。E. Crystallorophias 的眼睛几乎是 E. superba 和 E. triacantha 眼睛的两倍，这可能有助于在其冰下栖息地内保持视觉分辨率。在种内，我们发现上述形态特征在 E. crystallorophias 和 E. triacantha 中在性别和发育阶段之间差异不大，但在 E. superba 中差异显着。与雌性和幼体相比，雄性 E. superba 的眼睛和腹足明显更大，而雄性的甲壳在生长过程中随着体长的比例变得更短。这些特征表明雄性具有更大的搜索和游泳能力，我们假设，这增加了它们定位雌性并使雌性受精的能力。这种雄性 E 的形态特化。