The filariform larva is a characteristic developmental stage of which phylum?

Pseudocoelomate animals are a characteristic of this phylum.

Which one of the following phyla is characterized by the absence of a true coelom?

While trying to find out the characteristics of a newly found animal,a researcher performed histology on the adult animal and observed a cavity with the presence of mesodermal tissue towards the body wall,but no mesodermal tissue was observed towards the alimentary canal. What could be the possible coelom of that animal?

In $Aschelminthes$,the excretory tube removes body wastes from the body cavity through:

In the given figure,what does the part labeled '$a$' represent?