Answer:
X: Roundworms
Y: Flatworms
Step-by-step explanation:
The complexity of bilaterally symmetrical species is determined by the presence of a body cavity called a coelom. From simple acoelamates to complex coelomates, worms are animals capable of living freely, or in parasitic relationships with their hosts. They are often adapted for survival in specific environments.
These each belong to specific phyla:
- Segmented worms- Annelida. true coelom, complex systems of organs like a digestive and a circulatory system. e.g. earthworm
- Roundworms- Nematoda. show bilateral symmetry; sexually divergent (male, female), have an incomplete psuedocoelom; e.g. the giant roundworm- Ascaris
- Flatworms- Platyhelminthes. no coelom, or complex systems of organs. e.g. flukes