Question

The septal and pharyngeal nephridia open into the alimentary canal and are of enteronephric type. It is an adaptation for the
A. Conservation of water.
B. Conservation of heat.
C. Regulation of temperature.
D. Regulation of amino acids.

Answer 1

Nephridia are organs present in pairs in invertebrate animals and they resemble the vertebrate kidneys
in function. Nephridia are divided into three parts i.e., septal nephridia, pharyngeal nephridia, and
integumentary nephridia mostly in annelids and arthropods.

Complete answer:
Option (A) is correct. The septal and pharyngeal nephridia are of an enteronephric form and open into
the food canal. It is an adaptation for the conservation of water. The opening of these nephridia into the
an alimentary canal helps in the reabsorption of water, thereby conserving water.
Option (B) is incorrect. The main role of nephridia is to excrete out waster and perform the function of
osmoregulation that helps in maintaining the balance between the fluid and the electrolytes.
Options (C) is incorrect. The opening of septal and pharyngeal nephridia into the alimentary canal has
no role in regulating the temperature. This adaptation is meant for conserving water by reabsorbing
maximum water from the foodstuffs. During summers and winters, maximum reabsorption of water takes place making urine more hypertonic while during the rainy season the urine is more diluted as less reabsorption of water takes place during this season.
Option (D) is incorrect. The opening of the septal and pharyngeal nephridia into the alimentary canal
helps in osmoregulation but not the regulation of amino acids.

Hence, the correct option is (A).

Note:
Nephridia are meant for excreting out waste as well as helping in osmoregulation. These nephridia either open into the gut or the exterior through the nephridiopore. When the nephridia opens into the gut (septal and pharyngeal nephridia), it helps in the reabsorption of water thus serving as an organ for conserving water.