**Why is a liquid skeleton present in earthworms?**

Earthworms, belonging to the phylum Annelida, possess a unique feature called a liquid skeleton. This liquid skeleton serves as a substitute for a rigid skeletal system found in many other organisms. Let's delve into the details to understand the purpose and functioning of the liquid skeleton in earthworms.

**1. Structure of Earthworms:**
Earthworms have a long, cylindrical body with distinct segments called annuli. Each segment contains circular and longitudinal muscles, which aid in the worm's movement. The liquid skeleton plays a crucial role in facilitating these movements.

**2. Function of the Liquid Skeleton:**
The liquid skeleton in earthworms serves multiple functions that are vital for their survival and locomotion. These functions include:

- **Hydrostatic Support:** Unlike humans and other animals with a solid skeleton, earthworms rely on a hydrostatic skeleton for support. The liquid-filled coelom acts as a hydraulic system, providing support and maintaining the body's shape. The coelomic fluid, also known as the liquid skeleton, fills the body cavity and exerts pressure on the body wall, offering structural support.

- **Movement:** Earthworms exhibit peristaltic movement, which involves the contraction and relaxation of circular and longitudinal muscles along the body. The liquid skeleton enables this type of movement by transmitting the force generated by muscle contractions throughout the body.

**3. Peristaltic Movement:**
Peristaltic movement is crucial for an earthworm's locomotion. It involves a wave-like contraction and relaxation of muscles along the body. Here's how it works:

- Circular muscles contract in one segment, narrowing its diameter.
- Longitudinal muscles contract, shortening the segment's length.
- As a result, the anterior end is pushed forward, while the posterior end anchors itself using setae (bristles).
- The circular muscles relax in the next segment, allowing it to expand.
- The longitudinal muscles contract in the same segment, pulling the body forward.
- This process repeats, causing the worm to move in a wave-like manner.

**In conclusion, the presence of a liquid skeleton in earthworms is essential for their survival and locomotion. It provides hydrostatic support, maintaining the body's shape, and enables peristaltic movement. This unique adaptation allows earthworms to navigate through soil and contribute to the decomposition process, making them vital organisms in the ecosystem.

This liquid skeleton serves as a substitute for a rigid skeletal system found in many other organism.