鲤科鱼类前方椎体的形成及其在系统发育上的意义

本文对九种鲤科鱼类与中国胭脂鱼幼体的前方椎体的发育进行了比较。观察结果表明这两个科鱼类的前方椎体发育是近似的,它们的魏氏小骨有共同的来源;魏氏复合骨由前方椎体上方的第二骨化中心形成,这个骨化中心与第三和第四上神经骨相当。另一方面,胭脂鱼幼体的第二椎体副突已与第四椎体的胸肋相接;魏氏复合骨的扩展是骨化中心背脊部均匀地发生的,这些与鲤科有着明显的不同。鲤科幼体的魏氏复合骨发育具有共同的特点,第二骨化中心的前方有一棘状物在早期出现,它代表了第三上神经骨伸出部份。但随后的发育可以区分为两种不同方式:一种为雅罗系鱼类所具有,即第二骨化中心以棘状物的扩展为主,前、后棘存在并有缝合线相连;另一种为鲃系鱼类所有,即第二骨化中心的发育以其背中部伸出的实心嵴突为主,仅有不发达的前棘,此系属于派生性结构。与魏氏复合骨相关的是2—3椎体间的关系也有相应的差别:雅罗系鱼类的幼体其2—3椎体间分离(仅鳑(鱼皮)亚科鱼类例外),而鲃系鱼类的幼体其2—3椎体愈合。由于幼体魏氏复合骨与椎体的特征比成体表现更为明显,它们在系统发育上能提供更为清楚的信息。

DEVELOPMENT OF THE ANTERIOR VERTEBRAE IN THE CYPRINIDAE AND THEIR SIGNIFICANCE IN THE PHYLOGENSIS

The anterior vertebrae of nine species cyprinid juveniles,including Carassius cuvier,Cir- rhinus molitorella,Coreius sp.,Erythrcoulter sp.,Labeo lohita,Magalobrama terminalis,Pseu- dorasbora parva,Puntius gonionotus,Rhodeus sp.,and one species catostomid juveniles Myxo- cyprinus asiaticus have been studied.They are similar in structure to those in the juvenile of the characin,Brycon,but exhibit two ossification centers above the anterior vertebrae.The ante- rior center,which represents the second supraneural,forms a plate-like bone and the second one,which may be in connection with the third and fourth supraneural,becomes the webrian complex. In the early juvenile stage of cyprinids,a bony spine appears on the upper anterior margin of the second ossification center.Two types of weberian complex growth can be reco- gnized based on different developmental patterns of the bony spine.In Tribe Leuciscini spe- cies,the front and posterior bony spine both exist in the juvenile and enlarge themselves into the main part of the weberian complex,but in Tribe Barbini species the bony spine are weakly developed and a dorsal ridge processes from the second ossification center expands in front and behind the bony spine,forming a thin plate structure,which is the main part of the weberian complex. In agreement with the weberian complex development,the second and third vertebrae are seperated in most juveniles of Tribe Leuciscini.On the other hand,the second and third ver- tebrae are invariably fused in all juveniles of Tribe Barbini,representing a more derived con- dition.These two features of juvenile cyprinids provide clearer information on phylogenesis than the features of the adults.