Phosphatocopina - ostracode-like sister group of Eucrustacea
Phosphatocopina - ostracode-like sister group of Eucrustacea
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DOI：
10.1007/s10750-004-4944-6
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发表时间：
2005-04-01
期刊：
影响因子：
2.6
通讯作者：
Waloszek, D
中科院分区：
文献类型：
--
作者：
Maas, A;Waloszek, D
Phosphatocopina长期以来被认为是最古老的寒武纪介形类甲壳动物。然而，我们对来自瑞典上寒武统“奥斯滕”的2,500多个标本的详细分析表明，磷盾亚目既不是介形类，也不是真甲壳纲。研究的phosphatocopines的天线和下颌骨包括一个突出的肢体干进行两段内足和多环外足。现在，该茎部分被认为是个体发育期间基节和担子的融合产物。磷盾亚目与真甲壳纲有共同的特徴，例如触角和下颚上的基节和基足，以及腹侧的身体结构，例如突出的口前唇和单一的口后头板，胸骨（在下颚胸骨部分有副颌）。作为一种近形，Phosphatocopina的个体发育开始于具有四对肢体的“头部幼虫”，这是真节肢动物和甲壳动物的地面模式中发现的幼虫类型。相比之下，真甲壳动物的个体发育开始于一个有三对肢的无节幼体，一个“短头幼虫”或orthonaplius。同样，后下颌肢的磷酸介类保留了类形肢设计的一个有刚毛的“近端endite”的腹足动物，而Eucrustacea，包括介形类，有他们的第一个后下颌肢分化成一个“口器”，上颌骨。Phosphatocopina的特征是触角小，末端刚毛少，具背间双瓣盾，触角和下颌骨上的基节和基足融合。因此，我们认为Phosphatocopina是Eucrustacea的姐妹群。瑞典南部的上寒武统的各自的phosphatocopine物种仅限于一个特定的时区，可能是有用的地层标志。
The Phosphatocopina were long considered as the oldest, Cambrian, record of ostracode Crustacea. However, our detailed analysis of more than 2,500 specimens from the Upper Cambrian 'Orsten' of Sweden reveals that Phosphatocopina are neither Ostracoda nor Eucrustacea. The antenna and mandible of the phosphatocopines investigated consist of a prominent limb stem which carries a two-segmented endopod and multi-annulated exopod. This stem portion is now recognised as the fusion product of the coxa and basipod during ontogeny. Phosphatocopina share features, such as the coxa and basipod on antennae and mandibles, as well as ventral body structures such as the prominent pre-oral labrum and a single post-oral cephalic plate, the sternum (with paragnaths on the mandibular sternal portion), exclusively with the Eucrustacea. As a plesiomorphy, the ontogeny of Phosphatocopina starts with a 'head larva' with four pairs of limbs, a larva type found in the ground pattern of the Euarthropoda as well as the Crustacea. In contrast, eucrustacean ontogeny begins with a nauplius with three pairs of limbs, a 'short-head larva' or orthonauplius. Again, the post-mandibular limbs of phosphatocopines retain the plesiomorphic limb design of a basipod with a setiferous 'proximal endite', whereas Eucrustacea, including the Ostracoda, have their first post-mandibular limb differentiated into a 'mouthpart', the maxillula. Autapomorphies of Phosphatocopina include the small antennula with few terminal setae, a bivalved shield with interdorsum, and the fused coxa and basipod on antenna and mandible. We therefore consider the Phosphatocopina to be the sister group of the Eucrustacea. The respective phosphatocopine species of the Upper Cambrian of southern Sweden are restricted to a particular time zone and may be useful as stratigraphic markers.