TPO43 Integrated

The author of the reading passage points out three theories that agnostids, which were primitive arthropods-relatives of modern-day insects, may have lived in the past. Nevertheless, these are all refuted by the lecturer in the listening section.
In the first place, it is argued in the reading passage that agnostids were free-swimming predators who prey on plenty of smaller organisms in the ancient ocean owing to other types of primitive arthropods that we have known were strong swimmers and active predators, which means that it is reasonable to make the analogy. However, the lecturer rejects the argument, suggesting that while those primitive arthropods that we have known had well-developed eyes, agnostids had pretty tiny eyes and some of them may be even blind, which ultimately rules out this hypothesis. Or, agnostids may have sensory systems to help them view the world, but none of fossils reveal this function.
Furthermore, the author believes that agnostids were seafloor dwellers, given that there are examples of other types of primitive arthropods living this way and the analogy makes sense. In contrast, the theory is considered unpersuasive in the listening section considering that seafloor dwellers are someone who prefer to stay in a limited area, but, as the fossil revealed, agnostids are found living in multiple areas, saying that they had the ability to move fast, which is highly unusual feature for seafloor dwellers.
Lastly, agnostids were parasites is another hypothesis because there are many species of modern-day arthropods living as parasites. On the contrary, the lecturer claims that parasites are creatures whose population are not very large so that they will not kill out their host. But, in reality, there are vast of agnostids' fossil discovered, which rules out this theory again.