TAXONOMY AND HABITAT OF QUATERNARY LIMNOCYTHERE (OSTRACODA) FROM THE QAIDAM BASIN AND THE QINGHAIHU LAKE,QINGHAI
TAXONOMY AND HABITAT OF QUATERNARY LIMNOCYTHERE (OSTRACODA) FROM THE QAIDAM BASIN AND THE QINGHAIHU LAKE,QINGHAI
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作者：
Yangbo Fan
湖泊介形类是柴达木盆地和青海湖第四纪介形类动物群中数量最多、分布最广的成员之一，但其分类至今仍存在争议，许多学者将湖泊介形类划分为三个属，即L.sancti-patricii，L.binoda和L.inopinata，而其他作者将该属的大多数成员归为一个种--.inopinata.Re--。通过对研究区第四系和现代沉积物中大量分布的湖珊瑚化石的鉴定，发现该区没有发现具有L.dubiosa（背侧可见：雌性在壳中部前有深的横向凹陷;雄壳双侧近平行，右瓣较左瓣宽），上述文献报道的形态和描述均与青藏高原第四纪湖花介属（Limnocythere）无关联，在已鉴定的L.sancti-patricii中也未见标本，因为它巨大的体型在柴达木盆地和青海湖，甚至可能在中国所有的半干旱和干旱地区，已鉴定的物种为L.（非L. sancti-patricii）和L.（non L.sancti-patricii布雷迪et Robertson）分别为无节和单节的两种类型，因此瓣上的节是一种表型，因此，L.binoda是L.inopinata的次异名，L.inopinata在研究区的分布表明，该物种喜寡盐或中盐（特别是14‰的中盐），钙含量差，风平浪静（停滞的）沃茨，尽管它被认为是广盐性的，在低盐度的小苏干湖采集的5个样品中，（S=0.616‰-0.694‰），大部分样品中有大量的无节羊栖菜瓣，个别样品中有少量的有节羊栖菜（占物种总数的0.26%），而节头类则是青海湖的常见种在青海湖高盐度区（13.623‰ ~ 14.665 ‰），节瘤个体的平均含量为0.1%~ 9.1（平均1.7%），远高于小苏干湖样品，因此盐度的降低不是造成结瘤的直接原因（青海湖东南部的一个小湖，S=1.156‰），节状羊栖菜的含量有很大的增加，最高可达50%，这与该地区硅藻丰富、硅离子含量高相对应，因此，极高的SiO_2含量可能是导致L. inopinata结瘤的直接原因。
Limnocythere is one of the most abundant,widespread members in the Quaternary ostracod fauna from the Qaidam Basin and the Qinghaihu Lake,Qinghai Province,but its taxonomy in the study area,is controversial up to now.Limnocythere dubiosa,L.sancti-patricii,L.binoda and L.inopinata have been identified from the genus in the study area by many authors,and the other authors refer most members of the genus to one species —-.inopinata.Re-identification of a large number of Limnocythere distributed in Quaternary System and recent sediments from the study area shows that no valves which bear the species features of L.dubiosa(seen dorsally:female with deep transverse depressions before middle of the shell;male shell bilateral sub-parallel and right valve more extended than the left)have been found,and no above-mentioned figures and description for the Limnocythere species features reported in the literature are related to Quaternary Limnocythere from Qinghai-Xizang(Tibet)Plateau.In addition,the authors have not seen specimens in their identified L.sancti-patricii,for its distinguished large size(females 0.75 mm,males 0.80 mm),and have not seen the interrelated figures and descriptions with this size reported from the Quaternary System or recent sediment in the study area either.In the Qaidam Basin and the Qinghaihu Lake,even probably all the semi-arid and arid regions of China,the species identified L.dubiosa(non L.dubiosa Daday)and L.sancti-patricii(non L.sancti-patricii Brady et Robertson)are the individuals without node and with single node of L.inopinata,respectively.In consequence the nodes on the valves is a phenotypic nature,thus the name L.binoda is a junior synonym of L.inopinata.The distribution of L.inopinata in the study area indicates that the species prefers oligohaline or mesohaline(especially the mesohaline of 14‰),poor calcium content and calm(stagnant)waters,although it is regarded as a euryhaline,titanoeuryplastic and rheoeuryplastic species.In five samples collected from the oligohaline Xiaosuganhu Lake with lower salinity(S=0.616‰-0.694‰),there are a lot of valves of unnoded L.inopinata in most samples,and one sample has a few noded individuals(account for 0.26% of the species population),while the noded individuals occurs frequently in the Qinghaihu Lake(29 samples in 57 samples contain L.inopinata).In the Qinghaihu Lake,with the high salinity of 13.623‰-14.665‰,the noded individual is 0.1%-9.1%(average 1.7%)in L.inopinata populations,much higher than that from the samples of the Xiaosuganhu Lake mentioned before.Therefore,the decrease of the salinity is not the direct cause for nodation.In the Erhai Lake(a small lake to the southeast of the Qinghaihu Lake,S=1.156‰),a great increase in the noded L.inopinata content happens with a highest 50%,which corresponds with the abundant diatom and the high Silica ion in the region.Therefore,the extremly higher Silica is probably the direct reason for the nodation of L.inopinata.