In the reading passage, the author states three theories to tell us agnostids may have lived. However, the professor in the lecture thinks these theories have weakness so that they should be ruled out.
 
First, the writer claims that the agnostids may be free-swimming predators to catch smaller creatures. There were many smaller animals in the ancient ocean for them to hunt. On the contrary, the professor says free-swimming predators usually have big developed eyes and they can attract preys. If they were blind, they would not hunt animals in the sea. Chasing animals in the ocean should have good sense organs, but there are no evidence in the fossil record show that.

Second, the writer thinks that the agnostids may have lived on the bottom of sea. However, the professor holds an opposite view about this theory. She says they moved slowly because they did not have ability to move fast and far. 

Third, the author states that the agnostids lived as parasites on larger animals. However, the professor does not thin