Anatomy of finfish and shellfish

Unit 13 - Mollusca

13.2.13.Excretory System
Excretion is taken care of by—(l) a pair of kidneys or organ of Bojanus, and (2) a pericardial gland or Keber's organ.
Kidneys or organs of Bojanus
The two kidneys o nephridia are often termed as the organs of Bojanus, after the name of their discoverer. They are situated beneath the floor of the paricardial cavity, one on each side of the vena cava. They are derived from the true coelom (urocoels).
Each kidney is a long, dark, glandular tube open at both ends. It is bent upon itself like a broad U-shaped tube, with the loop posterior, the two ends anterior and the two I lying parallel and one above the other. The lower arm is bi spongy, glandular and thick-walled, forming the kidney proper, which opens anteriorly into the fluid filled pericardial c by a small ciliated reno-pericardial aperture. The dorsal a small, non-gandutar, lined by ciliated epithelium and walled, known as the ureter or urinary bladder, which anteriorly into the supra-branchial chamber by a small aperture, between the inner gill lamina and the visceral The bladders of both the kidneys intercommunicate by an aperture.

Fig 18. Unio. Excretory organs (left view)

Physiology of excretion
The ventral glandular portion the kidney extracts guanin and other nitrogenous waste products of metabolism from the coelomic pericardial fluid as v the blood supplied to the kidneys. The walls of the pericardial sinus are also glandular, and supposed to secrete waste mal from the blood into the coelomic cavity.
The ciliated epithelial lining of the bladder produces outgoing current, thus carrying excretory fluid iron glandular part to the supra-branchial chamber, which ie the excurrent siphon. There is reabsorption of salts in. th kidneys, which also serve in maintaining the blood concent by removing excessive water from it.
Keber's organ
The Keber's organ or the pericardial gland is a large reddish-brown glandular mass situated in front of the pericardium. It probably helps in excretion, discharging into the pericardium.