Final answer:
Annelids, such as earthworms and leeches, have a complete digestive tract with a separate mouth and anus, and they exhibit internal and external segmentation. They possess a true coelom, circulatory and nervous systems, and specialized body structures like chaetae for movement.
Step-by-step explanation:
The statement 'Annelids __________' is A. have a mouth that is separate from the anus. Annelids, such as earthworms and leeches, have a complete digestive tract with a separate mouth and anus. Choices B and E are incorrect because flatworms are not annelids and annelids do have internal segmentation. Choice C is incorrect because Annelids do not have pseudocoeloms; they have a true coelom that they use as a hydrostatic skeleton.
The phylum Annelida includes various species like earthworms, leeches, and polychaete worms. These organisms exhibit a segmented body plan featuring external and internal partitions called metameres. Metamerism provides the evolutionary advantage of allowing for different segments to develop specialized functions. Annelids are bilaterally symmetrical vermiform creatures with complex systems such as a closed circulatory system, a well-developed nervous system, and a complete digestive system featuring a mouth, pharynx, esophagus, crop, gizzard, and intestine that ends in an anus.
Moreover, they have chaetae, which are hair-like structures that aid in locomotion, and in the case of polychaetes, parapodia that can act in both movement and gas exchange. While they lack a highly developed respiratory system, annelids perform gas exchange through their moist body surface, facilitated by their circulatory system. Excretion is carried out with metanephridia, essentially serving as the kidney for these organisms.