Study on morphology, ecology, biogeography and systematics of primitive ostracod Platycopa

本研究以日本原生介形类扁形目的一个分类群--结果表明，在实验条件下，附着于双环木假根周围的沉积物中采集到的个体数量最多。为了更详细地了解其栖息地和行为，对一些活体标本进行了观察。结果表明：该虫仅利用触角、触角和叉进行活动，其栖息地不在地表，而在粗沙粒间。本文认为，扁形目其他种的基本体型与Keijcyoidea sp.相同，生活方式也基本相同。这些知识将支持对原始介形类扁形目进化的认识。1）它们的个体发育有9龄。2)雌雄交配器在A-3（6龄）时均为原基，在此期间及以后出现性二型。3)该分类群的诊断特征，例如有节树干、双枝触角出现在早期阶段。4)它们有无节幼体的眼睛。5)肛口位于腹侧而非背侧。6)在肛门段之后存在一个单位，它是一个尾节。7)尾支衍生出一对肢状器官“叉”，与Podocopina的“尾支”不同源。8)分叉继续发展，直到最后的换羽。9)雌雄的交配器官均起源于第4干节。

This research focused on Keijcyoidea sp. which is a taxon of primitive ostracod Platycopa from Japan.There is no report on the ecology and habitat of Platycopa at all. In the experience, the largest number of individuals were collected from the sediments which attached around the rhizoid of Eisenia bicyclis. In order to know the habitat and behavior in detail, some living specimens were observed. As a result, the following facts became clear : they use only antennule, antenna and furcae for moving ; their habitat in not surface but between coarse sand grains. It is suggested that other Platycopa species must have almost the same life style because the basic body plan of them is common to the Keijcyoidea spThe following points of ontogeny and comparative anatomy were made clear. These knowledge will support the understandings of evolution on the primitive ostracod Platycopa.1) They have 9 instars in ontogeny. 2) Copulatory organs of both sexes appear in A-3 (6th instar) as anlagen and the sexual dimorphism is observed in and after this stage. 3) Diagnostic characters of this taxon e.g. articulate trunk, bi-ramous antenna appear in the early stages. 4) They have nauplius eyes. 5) the anal opening are located at not dorsal side but ventral side. 6) An unit exists after the anal segment ; it is a telson. 7) The telson derives a pair of limb-like organ 'furcae' which is not homologous to 'caudal rami' in Podocopina. 8) furcae continue to develop until the final moult. 9) The copulatory organs of both sexes are derived from the 4th trunk segment.