Excretion in Mollusca

• Excretion in Mollusca:-
Molluscan excretion takes place by the kidney (organ of Bojanus) & Keber’s organ. The kidney in bivalvian molluscs is known as organ of Bojanus.
Excretion in Unio sp. or Lamellidens sp. takes place by – 1. A pair of organ of Bojanus & 2. Keber’s organ or pericardial gland.
1. Organ of Bojanus:-
Kidneys of bivalves are called organ of Bojanus after the name of the discoverer.
Location:-
These are situated one on each side of the body below the pericardium.
Structure:-
Each kidney or organ of Bojanus is a long, dark tube, open at both ends. It consists of 2 parts -
1.  Brown, spongy, thick-walled, glandular part or kidney proper &
2.  Small, thin-walled, non-glandular, ciliated urinary bladder.
The glandular part of the kidney opens into the pericardium by renopericardial aperture.
The urinary bladder opens to the suprabranchial chamber of the mantle cavity,  by a minute opening, called renal aperture/ nephridiopore.
Physiology of excretion:-
Urine originates as an ultrafiltrate from the heart into the pericardium. 
The glandular part of the kidney extracts guanin & other nitrogenous waste products of metabolism from the coelomic pericardial fluid. Here resorption of the minerals & water takes place.
 The ciliated epithelial lining of the urinary bladder produces an outgoing current which takes away excretory product like NH3 & urea etc. to the outside through renal aperture, suprabranchial chamber & exhalant siphon respectively .
1. Keber’s organ:-
It is also known as pericardial gland. It is a large, reddish brown, glandular mass situated in front of the pericardium, & responsible for the excretion of nitrogenous waste products. The excretory products are discharged into the pericardium from where these are collected by the organ of Bojanus to be discharged to the outside.