Excretory organs of Earthworms are –
A) Coelom
B) Flame cells
C) Nephridia
D) Gizzard

Hint: Earthworm, also known as Pheretima, features a well- established excretory system. Excretory system helps in removing waste substances from the body.

Complete Answer:
Excretion is defined as the process of removal of metabolic waste products such as nitrogenous materials e.g. uric acid, urea, ammonia, amino acid, etc from the body. The excretory system of the earthworms being well-developed, consists largely of minute, glandular, and coiled segments of excretory tubules known as nephridia. The excretory cells present within the freshwater invertebrates are known as the flame cells.

Option A: Coelom forms serves as the excretory organs in Mollusca. Here, the coelom features a pericardial coelom around the heart of the organism; whereas paired coelom ducts along with gonadal coelom are commonly referred to as excretory organs. Thus, this is an incorrect answer for the given question.
Option B: Flame cells are defined as the specialised excretory organs of the representatives of the genera of freshwater invertebrates such as rotifers. Earthworms are not freshwater invertebrates. Thus, this is an incorrect answer for the given question.
Option C: Nephridia are well-developed excretory systems of the annelids. Earthworm is a representative of the group of Annelids. Thus, this is the correct answer for the given question.
Option D: Gizzard forms the part of the insects' alimentary canal which serves as a mediator for crushing down the food particles. Thus, this is an incorrect option for the given question.

Thus, the correct option is C) nephridia.

Note: Nephridia exists in two basic categories –
- Protonephridia - It is seen in simple freshwater organisms, rotifers, etc.
- Metanephridia - It is commonly seen in flatworms.