Fisheries

Until fairly recently, myxinoids and lampreys were regarded as being sepa-rately derived from fossil agnathan groups, but some workers provided mor-phological evidence for their closer relationship (e.g. Yalden, 1985), and the advent of molecular taxonomy has supported this, so they now lie together for most ichthyologists as a sister group …

In all fish, the body is built around an axial notochord, still present in adult agnathans, sturgeons, and Latimeria, but more or less reduced in most adult fish by the development of vertebral elements around it. This provides the incompressible strut flexed by the serial myotomal muscle blocks, and pro-tects …

The ancient fish ancestors were presumably small and fusiform, looking somewhat like amphioxus (Branchiostoma), and many modern fish have retained this streamlined kind of shape, built around an axial notochord, more or less reduced in most by the development of vertebral elements around it. But every other kind of body …