Schultze Hans-Peter, Arratia Gloria
Museum of Natural History and Department of Systematics and Ecology, The University of Kansas, Lawrence, Kansas 66045-2454.
J Morphol. 1988 Mar;195(3):257-303. doi: 10.1002/jmor.1051950304.
The vertebral centra of Hiodon, Elops, and Albula are direct perichordal ossifications (autocentra) which enclose the arcocentra as in Amia. An inner ring of ovoid cells forms in late ontogeny from the intervertebral space inside the autocentrum. The chordacentrum is reduced or completely absent in centra of adult Elops, whereas it forms an important portion of the centra in adult Hiodon. The posterior portion of the compound ural centrum 3+4+5 is partially (Hiodon) or fully formed by the chordacentrum (Elops, Albula). The haemal arches and hypurals are fused medially by cartilage or bone trabecles of the arcocentrum with the centra, even though they appear autogenous in lateral view in Elops and Albula. The composition of the caudal skeleton of fossil teleosts and the ontogeny of that of Hiodon, Elops, and Albula corroborate a one-to-one relationship of ural centra with these dorsal and ventral elements. The first epural (epural 1) of Elops relates to ural centrum 1, whereas the first epural (epural 2) of Hiodon and Albula relates to ural centrum 2. In Albula, the first ural centrum is formed by ural centrum 2 only. With 4 uroneurals Hiodon has the highest number within recent teleosts. Juvenile specimens of Hiodon have eight, the highest number of hypurals within recent teleosts; this is the primitive condition by comparison with other teleosts and pholidophorids. Reduction of elements in the caudal skeleton is an advanced feature as seen within elopomorphs from Elops to Albula. Such reductions and fusions occur in osteoglossomorphs also, but the lack of epurals and uroneurals separates most osteoglossomorphs (except Hiodon) from all other teleosts.
海鲢、海鳗和北梭鱼的椎体中心是直接的围索骨化（自椎体），像弓鳍鱼一样包绕着弧椎体。在个体发育后期，自椎体内部的椎间隙会形成一圈卵形细胞。在成年海鳗的椎体中，脊椎体缩小或完全消失，而在成年海鲢的椎体中，它构成了椎体的重要部分。复合尾椎体3 + 4 + 5的后部部分（海鲢）或完全由脊椎体形成（海鳗、北梭鱼）。脉弓和尾下骨在中间通过弧椎体的软骨或骨小梁与椎体融合，尽管在海鳗和北梭鱼的侧视图中它们看起来是自生的。化石硬骨鱼的尾骨骼组成以及海鲢、海鳗和北梭鱼的尾骨骼个体发育证实了尾椎体与这些背侧和腹侧元素之间的一一对应关系。海鳗的第一上尾骨（上尾骨1）与尾椎体1相关，而海鲢和北梭鱼的第一上尾骨（上尾骨2）与尾椎体2相关。在北梭鱼中，第一尾椎体仅由尾椎体2形成。海鲢有4个尾神经骨，在现存硬骨鱼中数量最多。海鲢的幼体标本有8个尾下骨，在现存硬骨鱼中数量最多；与其他硬骨鱼和褶鳞鱼相比，这是原始状态。从海鳗到北梭鱼的海鲢形鱼类中，尾骨骼元素的减少是一个高级特征。这种减少和融合在骨舌鱼中也会发生，但大多数骨舌鱼（除海鲢外）没有上尾骨和尾神经骨，这使它们与所有其他硬骨鱼区分开来。
