What is the function of Keber's Organ in Unio?

The correct answer is Excretory.
Key Points

• Unio is a genus of medium-sized freshwater mussels, aquatic bivalve mollusks (Phylum Mollusca) in the family Unionidae, the River mussels.
• Unio is the type genus of the family Unionidae.

Keber's organ

• It is the excretory organ in certain organisms like molluscs (which includes - Mussels, snail, octopus, clams etc.).
• It is otherwise also called as 'pericardial gland'.
• Keber's organ function is similar to that of the kidney and are present in addition to the kidneys (organ of Bojanus). 
• Structure:
  • ​It is a large, reddish-brown glandular mass.
• Location:
  • It may be over the auricle surface (articular glands), on the pericardium (pericardial glands), or in both positions. i.e., situated antero-lateral to the pericardium into which it discharges the waste material.
  • They are collected from that point by the kidney.
• Function:
  • The organ is responsible for the removal of nitrogenous wastes.
  • The wastes are excreted into pericardium from where these are collected by the 'organ of Bojanus' to be discharged outside the body. 

• Pericardial glands of bivalves have revealed that these consist of podocytes where the base of cytoplasmic extensions gives rise to numerous pedicels.

• These form a net with slits through which the fluid is filtered.

Additional Information

Unio: Organs and their function

• Excretory organ: The excretory system of Unio includes a pair of kidneys (organs of Bojanus), a pericardial gland (Keber's organ).
• Vascular: The blood vascular system is well developed and is of open type. It comprises the blood, heart, pericardium, arteries, sinuses, and veins.
• Digestive: The liver is the only digestive gland that surrounds the stomach. It secretes digestive enzymes and its cells are capable of ingesting food particles where intracellular digestion (i.e. digestion occurs in a cell) also occurs. 
• Reproductive: In Unio, the sexes are separate (dioecious) but there is no sexual dimorphism.

About Phylum Mollusca

• Mollusks are terrestrial or aquatic (marine or freshwater) animals having a calcareous shell.
• The body is covered by a calcareous shell and is un-segmented with a distinct head, muscular foot, and visceral hump.
• A soft and spongy layer of skin forms a mantle over the visceral hump.

Unio (Fresh-water Mussels)

• It belongs to bivalve molluscs.
• The animal is sedentary and eventually settles down on the bottom of the river or the lake through the mud or sand.