gills

But its wormy shape gives it the ability to swim right into the gills of fish, where it drinks its fill of blood.

Their secret to success lies within: Symbiotic bacteria live inside their gills and help them meet their nutritional needs, forming such a close relationship that these clams couldn't survive without their little companions.

"Depending on the contaminant and its chemistry, if it is small enough to pass through the gills of the mussel, it has the potential to accumulate in their tissue or precipitate within the hard-shell structure."

Their faces are featureless except for a crown of frilly pink gills.

Second, its parapodia are covered in gills, while most ragworms absorb oxygen through their parapodia without the aid of true gills.