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Study on plesiomorph and phylogeny of "living fossil" Ostracoda (Crustacea)

“活化石”介形纲（甲壳纲）的拟形体及系统发育研究

基本信息

批准号：
14340267
负责人：
TSUKAGOSHI Akira
金额：
$ 9.41万
依托单位：
Shizuoka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14340267/
关键词：
Ostracoda Crustacea living fossil evolution body segment Taxonomy diversity relict species 祖先形質原始性分類

项目摘要

A new species of genus Keijcyoidea with some plesiomorphic characters such as simple hingement, biramous antenna, clear body segments of urosom, was described as Keijcyodea infralittoralis Tsukagoshi, Okada and Horne, 2006. And its ecological nature (habitat and behavior) was also showed. Furthermore, all appendages and carapaces of all instars through the ontogeny were completely illustrated and described in the first time in Platycopida. The seventh limb which is lacking in adult was observed in younger juvenile. Therefore the lacking of the seventh limb is an autapomorphic character and the existence in younger instar suggests that Platycopida and Podocopida share a common ancestor. Though the appendage additional pattern is largely different from the Podocopida, it is suggested that the difference comes from the habitat and behavior in coarse sand sediments rather than the phylogenetical reason.It is well known that common ostracods use the apical point of mandible for opening the both valves. But the platycopan ostracods including Keijcyodea infralittoralis do not so develop the point of mandible. After detail observations, the two new facts were regarded, i.e. : 1)the furcral point of inner carapace surface, which corresponds to the apical point, sifts to anterior side in platycopans ; 2)the anterior sifted furcral point corresponds to the humb-like process in the basal part of antenna in Platycopida. These facts mean that the platycopans do not use the mandible but the antenna for valve opening. The difference is also supported by the observation of muscle network system. The method for valve opening must come from the evolution of eating habit.

本文报道了一新种，命名为Keijcyodea infralittoralis Tsukagoshi，Okada and Horne，2006。同时也揭示了其生态学性质（生境和行为）。此外，首次在扁形目中完整地描述了各龄期的附肢和背甲。成年人缺乏的第七肢在年轻的少年中观察到。因此，第七肢的缺失是一种自形特征，且在低龄阶段的存在表明扁足目和足目具有共同的祖先。尽管附肢附加模式与足介类有很大差异，但这种差异可能是由于它们在粗砂沉积物中的生境和行为而非生物学原因造成的。但包括下滨凯氏介形类在内的扁形类介形类的下颌骨尖并不发达。通过详细的观察，提出了两个新的事实：1）扁形目内甲壳表面的叉点，即对应于顶端的叉点，向前方筛出; 2）前筛叉点对应于扁形目触角基部的驼峰状突起。这些事实意味着，鸭嘴兽不使用下颌骨，而是使用触角来打开瓣膜。这种差异也得到了肌肉网络系统观察的支持。阀门打开的方法必须来自饮食习惯的演变。