Braun C B
Department of Neurosciences, University of California at San Diego, La Jolla 92093-0201, USA.
Brain Behav Evol. 1996;48(5):262-76. doi: 10.1159/000113205.
Despite the ancient origins and aberrant appearance of living jawless fishes, none of their features may be assumed to be primitive without comparisons among hagfishes, lampreys, and gnathostomes, and with the nearest relatives of all craniates, the cephalochordates. In this review, the sensory capabilities of lampreys and hagfishes will be compared, and the major features of early craniate sensory evolution will be infered using cladistic methodology and an accepted phylogeny of the hagfishes, lampreys and gnathostomes. Lampreys have well developed olfactory, visual and octavolateralis systems, each of which is known to play a role in lamprey life and behavior. Hagfishes have poorly developed visual and octavolateralis systems, but elaborate olfactory and chemosensory systems. Unfortunately, the natural behavior and lifestyle of hagfishes are poorly known, limiting our understanding of hagfish sensory biology. Both groups of living jawless fishes show mixtures of primitive and secondarily derived sensory features and have few shared derived sensory features that would indicate close relations between the two groups.
尽管现存的无颌鱼类起源古老且外形怪异，但如果不将盲鳗、七鳃鳗和有颌类动物进行比较，不与所有有头动物最近的亲属头索动物进行比较，就不能认为它们的任何特征是原始的。在这篇综述中，将比较七鳃鳗和盲鳗的感官能力，并使用分支系统学方法和已被接受的盲鳗、七鳃鳗和有颌类动物的系统发育关系来推断早期有头动物感官进化的主要特征。七鳃鳗拥有发育良好的嗅觉、视觉和八侧线系统，已知每个系统在七鳃鳗的生活和行为中都发挥着作用。盲鳗的视觉和八侧线系统发育不良，但嗅觉和化学感应系统却很精细。不幸的是，人们对盲鳗的自然行为和生活方式了解甚少，这限制了我们对盲鳗感官生物学的理解。这两类现存的无颌鱼类都表现出原始和次生衍生感官特征的混合，几乎没有共同的衍生感官特征表明这两类动物之间存在密切关系。
