Higashi Ryouichi, Tsukagoshi Akira
Department of Geosciences, Faculty of Science, Shizuoka University, Oya 836, Shizuoka City, 422-8529 Japan.
Zookeys. 2012(193):27-48. doi: 10.3897/zookeys.193.2842. Epub 2012 May 14.
Two new species of the interstitial ostracod genus Parvocythere, Parvocythere gottwaldisp. n. and Parvocythere gracilissp. n., are herein described. Although these two new species are clearly distinguishable by certain morphological differences in elements of the male copulatory organ, and the carapace, they share the following simplified characters of the appendages and male copulatory organ: antennular fourth podomere with no suture; reduced claws on the distal end of antenna; and asymmetric male copulatory organ. The morphological differences among known and new Parvocythere species suggest that the species of this genus can be classified into two groups by the presence/absence of the suture on the antennular fourth podomere. The "Group S" is characterised by the presence of the antennular suture, and all species of this group have a two-clawed antenna and symmetric male copulatory organ, characters which are generally seen in cytheroid ostracods. The species belonging to "Group N" are characterised by the absence of the suture, regarded as a pedomorphic character, show the following characters: two clawed or one clawed antenna, and symmetric or asymmetric male copulatory organ. The morphological variation within Group N includes reductive characters regarded as an adaptation to the narrow spaces of the interstitial environment of a sandy beach. These intrageneric morphological variations of the exclusively interstitial genus Parvocythere suggest the possibilities that Group N might be derived from Group S, and that some adaptive characters to an interstitial environment could have developed after the colonisation of these environments.
本文描述了介形虫属Parvocythere的两个新物种，即戈特瓦尔德小浪花介Parvocythere gottwaldisp. n.和纤细小浪花介Parvocythere gracilissp. n.。尽管这两个新物种在雄性交配器官和头胸甲的某些形态差异上明显可区分，但它们在附肢和雄性交配器官上具有以下简化特征：触角的第四小节没有缝线；触角末端的爪减少；雄性交配器官不对称。已知和新的Parvocythere物种之间的形态差异表明，该属的物种可以根据触角第四小节上是否有缝线分为两组。“有缝线组”的特征是触角有缝线，该组的所有物种都有双爪触角和对称的雄性交配器官，这些特征通常见于浪花介形虫。属于“无缝线组”的物种的特征是没有缝线，这被视为幼态延续特征，具有以下特征：双爪或单爪触角，以及对称或不对称的雄性交配器官。无缝线组内的形态变异包括被认为是对沙滩间隙环境狭窄空间的适应的简化特征。专门生活在间隙环境中的Parvocythere属内的这些形态变异表明，无缝线组可能源自于有缝线组，并且在这些环境定殖后可能已经形成了一些对间隙环境的适应性特征。
