Phylum annelida: Segmented worms and leeches!
A fun and potentially awkward fact: The Latin word "annellus" means "little ring." Members of this phylum are segmented into ringlets.
Pictured here is an earthworm: there's plenty more to them than you'd think. However, their lack of lungs forces them to absorb oxygen from the soil! The dorsal blood vessel absorbs the oxygen and it travels to the hearts-ten of them!- from the esophagus, before being taken into the ventral blood vessel, which then pumps the oxygen throughout the worm.
The cardiovascular system is quite similar among some annelids. Leeches are open-circulatory annelids, where blood flows at a slower pace due to lack of smooth internal muscles. The blood flows freely within the leech! Otherwise, however, they're very similar to worms.
However, polychaetes, a type of marine worm, don't have this system at all!
Pictured here is an earthworm: there's plenty more to them than you'd think. However, their lack of lungs forces them to absorb oxygen from the soil! The dorsal blood vessel absorbs the oxygen and it travels to the hearts-ten of them!- from the esophagus, before being taken into the ventral blood vessel, which then pumps the oxygen throughout the worm.
The cardiovascular system is quite similar among some annelids. Leeches are open-circulatory annelids, where blood flows at a slower pace due to lack of smooth internal muscles. The blood flows freely within the leech! Otherwise, however, they're very similar to worms.
However, polychaetes, a type of marine worm, don't have this system at all!