Elopiformes is one of the most ancient orders of Teleostei fishes and includes the Megalopidae and Elopidae families. Although relevant to scientific research, cytogenetic and molecular data are lacking for both families. Here, we compared Elopiformes species from the perspective of genetic divergence and cytogenetics to elucidate the chromosomal diversification and evolutionary processes of Elopiformes. The cytogenetic results showed that Megalops atlanticus and Elops smithi are 2n = 50, with differences in their chromosomal formulas. The distributions of heterochromatin and repetitive DNA sequences revealed many characteristics shared between Elopiformes and other basal lineages of Teleostei fishes. In addition, the results suggested that different chromosomal rearrangements have occurred in the analysed Elopiformes species. The species tree indicated that Megalopidae and Elopidae were monophyletic groups, but the genetic divergence was higher for Megalops species than for Elops species. The small divergence and sympatric distribution of Elops species may not prevent hybridization. However, the karyotype differentiation may be an effective post-zygotic mechanism preventing continuous hybridization, and it could be the key factor in this speciation process. In conclusion, this is the first report of Elopiformes species that integrates molecular and cytogenetic data. Our results emphasize the importance of cytogenetic data for further defining Elopidae species.

蛇形目是Teleostei鱼类最古老的习性之一，其中包括巨嘴兽科和蛇形科。尽管与科学研究有关，但两个家族都缺乏细胞遗传学和分子数据。在这里，我们从遗传差异和细胞遗传学的角度比较了蛇形目物种，以阐明蛇形目的染色体多样性和进化过程。细胞遗传学结果显示大西洋巨Mega和史密斯巨E。是2n = 50，它们的染色体公式不同。异染色质和重复DNA序列的分布揭示了Elopiformes和Teleostei鱼的其他基础谱系之间共有的许多特征。此外，结果表明在分析的埃洛皮亚种中发生了不同的染色体重排。物种树表明，Megalopidae和Elopidae是单系种群，但是Megalops物种的遗传差异高于Elops物种。小分歧和同域分布Elops种可能无法阻止杂交。然而，核型分化可能是防止连续杂交的有效的合子后机制，并且可能是该物种形成过程中的关键因素。总而言之，这是首次整合分子和细胞遗传学数据的类钩虫物种报告。我们的结果强调了细胞遗传学数据对进一步定义蛇科的重要性。