In some gastropods, the nephridium opens directly into the sinus, but more usually, there is a small duct, referred to as the "'renopericardial canal " '.
12.
To me the most recognizable feature of true segments or somites in animals is that each one has a single unit of excretory tissue-see nephridium and nephrostome, though in vertebrates the pronephros regresses.
13.
The most primitive gastropods retain two nephridia, but in the great majority of species, the right nephridium has been lost, leaving a single excretory organ, located in the anterior part of the visceral mass.
14.
In the lancelet "'Hatschek's pit "', not to be confused with "'Hatschek s nephridium "', is a deep ciliated dorsal midline of the buccal cavity ( the region of the gut behind the mouth ) Among other things, it secrets mucus which entraps food particles from the water.
15.
This tubule then leads to the main body fluid filtering organ, the nephridium or metanephridium, which removes metabolic waste from the digestive tract, which runs straight through from mouth to anus without coiling, and is flanked above and below by blood vessels ( the dorsal blood vessel and the ventral blood vessel as well as a subneutral blood vessel ) and the ventral nerve cord, and is surrounded in each segment by a pair of pallial blood vessels that connect the dorsal to the subneutral blood vessels.
