Feeding mechanism of Branchiostoma. (IFS 2021/8 Marks)

Introduction:

Branchiostoma, commonly known as lancelets or amphioxus, are small marine invertebrates that belong to the subphylum Cephalochordata. They are filter feeders, meaning they obtain their food by filtering particles from the water.

Feeding Mechanism of Branchiostoma (Amphioxus)

1. Water Intake

• Water enters the mouth of Branchiostoma through the oral hood.
• The oral hood is a large, ciliated structure that aids in directing the water towards the mouth.
• This process is passive, driven by the animal's swimming motion.

2. Ciliary Action

• Cilia lining the gill slits and the oral cavity play a crucial role in creating water currents.
• The cilia beat in a coordinated manner to push the water through the pharyngeal gill slits.

3. Filtration

• The pharyngeal gill slits are lined with mucous-producing cells that trap plankton, bacteria, and organic particles.
• As the water passes through the slits, the particles get stuck in the mucus, and clean water flows out through the atriopore.

4. Transport of Food

• The trapped food particles are then transported to the intestine via the ciliary action and mucus.
• The mucus helps in moving the food particles along the pharyngeal region towards the digestive tract.

5. Digestion and Absorption

• The ingested food particles are further processed in the digestive tract.
• Digestion occurs within the gut, and nutrients are absorbed by the cells lining the intestine for energy and growth.

6. Excretion of Waste

• The excess water and waste products that do not contain nutrients exit through the atriopore, maintaining the flow of water through the system.

Conclusion:

Branchiostoma have a unique feeding mechanism that allows them to efficiently filter feed and obtain nutrients from the water. Their ciliary feeding mechanism, mucus secretion, and pharyngeal slits all play a role in this process.