other acoelomates
Phylum Gnathostomulida:
This phylum contains about 80 species of tiny marine worms. These worms are unique due to the presence of a pair of hard jaws. They live mainly along the coastal shorelines and use their hard jaws to scrape fungi and bacteria from the particles.
Gnathostomulids have no coelem or pseudocoelem , and there is only one opening from their digestive cavity.
Phylum Rhynchocoela:
Phylum Rhynchocoela includes about 650 species of acoelomate worms, commonly called ribbon
worms or nemertines. They are characterized by a proboscis; a long, retractile, slime-covered hollow
tube, which may be armed with a barb. They use the proboscis to capture prey. Some inject a paralyzing
poison into their prey.
Unlike the digestive cavity of cnidarians and flatworms, ribbon worms have a one-way digestive
track beginning with a mouth and ending with an anus. The two-opening tract is much more efficient than
the one opening arrangment because eating can be continuous and various segments of the tract can
become specialized for different stages of digestion.
For reproduction in ribbon worms, fertilization occurs externally. Also, asexual reproduction may
result by fragmentation of the body and regeneration of whole worms from the parts.
Gnathostomulida:
Rhynchocoela: