Description of the postembryonic stages of Boeckella poopoensis (Crustacea, Copepoda, Centropagidae)

ABSTRACT Boeckella poopoensis Marsh, 1906 is one of the most common copepods in the saline lakes of South America, where generally is the species that greater contributes to the zooplankton community biomass. Despite of its wide geographic distribution and ecological importance, the characteristics of the postembryonic stages are unknown, which prevents a detailed understanding of the structure and dynamics of natural populations. The objective of this work was to describe the morphology of the postembryonic stages and to compare it with other species of Centropagidae. The specimens were obtained from a monospecific culture acclimatized in the laboratory. The lineage comes from El Carancho shallow lake (65°03’W, 37°27’S). The identification of the postembryonic stages was performed according to the characteristics established for copepod calanoids. Based in all developing stages, some characteristics that distinguish B. poopoensis from another species of the genus are: lobes of nauplii with the same number of setae of equal length; beginning of body segmentation from nauplii III; sexual dimorphism from copepodite IV (although only evident in the V leg); the endopod of the V leg of copepodites V males and females are biarticulate, but while females endopod add setae respect to the previous stage, males endopod lose them and remain glabrous as in the adults. Copepodites V do not present characteristics typical of adults, such as, the most developed thoracic left wing of females and in the geniculate right antenna of males. All stages of B. poopoensis are larger than those corresponding to other species of centropagids, and in the immature stages, the appendages show their own patterns of setae and have a slightly smaller number of setae than that of the other species of the family.

摘要：1906年由Marsh描述的布氏博克水蚤（Boeckella poopoensis Marsh, 1906）是南美盐湖中最常见的桡足类（copepods）之一，通常是对当地浮游动物群落生物量贡献最大的物种。尽管其地理分布广泛且生态重要性突出，但目前对其胚后发育阶段（postembryonic stages）的特征仍不明确，这阻碍了对其自然种群结构与动态的深入理解。本研究旨在描述该物种的胚后发育阶段形态，并与剑水蚤科（Centropagidae）其他物种进行比较。实验所用标本取自实验室驯化的单种培养种群，其起源于埃尔·卡兰乔浅湖（El Carancho，65°03’W，37°27’S）。胚后发育阶段的鉴定依据哲水蚤类（calanoids）桡足类的既定分类特征。基于所有发育阶段的观察结果，本研究发现了若干可区分布氏博克水蚤与该属其他物种的形态特征：无节幼体（nauplii）的叶状突起具有数量相等、长度一致的刚毛（setae）；自无节幼体III期起出现体节分化；从桡足幼体IV期（copepodite IV）开始出现雌雄二型性（sexual dimorphism，该特征仅在第V胸足上有所体现）；第V期桡足幼体（copepodite V）雌雄个体的第V胸足内肢均为双节结构，但雌性内肢相较于前一发育阶段新增了刚毛，而雄性内肢则丢失了刚毛，与成体一样光滑无毛。第V期桡足幼体尚不具备成体的典型特征，例如雌性最发达的左胸翼以及雄性的膝状右触角。布氏博克水蚤的所有发育阶段均大于剑水蚤科其他物种，且在未成熟阶段，其附肢的刚毛模式独具特色，刚毛数量略少于该科其他物种。