If so many sea animals evolve to “craboforms” because it is so evolutionarily advantageous, what about fish-forms?

Question

Fish are so abundant in the ocean (even given how humans overfish, and them often being prey), I kind of wonder

1. Why don’t marine animals converge to a more fish like form? (Aside from say land mammals like whales and dolphines who decided they want to go to the sea)

2. What benefits are there in having a fish-like form in the ocean? It must be evolutionarily advantageous for some reason.

3. Did the first non microscopic multicellular beings have fish-form?

In: Biology

Answer 1

I think part of the issue is the craboform isn’t only a sea thing.  Multiple different branches ended in craboform.  Like public lice.