Final answer:
To argue that a new species is more closely related to nematodes rather than annelids, one should look for characteristic features like a pseudocoelom. The presence of a hemocoel would be such an indication, which aligns with the characteristic body cavity of nematodes, differentiating it from the true coelom of annelids. The correct answer is option a.
Step-by-step explanation:
If you find an animal that you believe is a new species and you want to argue that it is more closely related to a nematode than it is to an annelid, you would need to look for specific characteristics that are common in nematodes but not in annelids. Characteristics such as a distinct mouth and anus are typical of nematodes but not unique to them, as many other animals also have this feature. However, nematodes are known for their pseudocoelom, a type of body cavity, and have a complete digestive system with a separate mouth and anus which is not a characteristic seen in flatworms. Nematodes also have a collagenous/ chitinous cuticle that requires them to molt periodically during growth. These features are distinct from annelids, which are known for their segmented body and true coelom.
With that in mind, the characteristic that would best support the argument that the animal is more closely related to a nematode is a. it has a hemocoel, since this suggests the presence of a pseudocoelom, characteristic of nematodes, and not the true coelom found in annelids.