Digestive System Of Balanoglossus

Balanoglossus is a marine, worm-like organism belonging to the phylum Hemichordata. It is commonly known as an acorn worm and is considered an evolutionary link between invertebrates and chordates due to its possession of some primitive chordate characteristics. Balanoglossus is a burrowing animal found in shallow coastal waters, inhabiting U-shaped burrows in sandy or muddy substrates.

1.0Classification 

• Kingdom: Animalia
• Phylum: Hemichordata
• Class: Enteropneusta
• Order: Enteropneusta incertae sedis
• Genus: Balanoglossus

2.0Habit and Habitat

• It is marine and cosmopolitan.  
• It is tubicolous, living in U-shaped burrows excavated in the sandy bottom.  

3.0External Morphology 

• The body of Balanoglossus is soft, elongated, and cylindrical, with a rich ciliation across its surface and a mucus coating.
• Its length ranges from 2 cm to 2.5 meters,

4.0Body Division 

• 1. Proboscis or Protostome
• 2. Collar or Mesosome 
• 3. Trunk or Metastome

1. Proboscis:- 

• Anterior, muscular, and ciliated
• Helps in food collection and burrowing
• Contains a proboscis coelom that opens via a proboscis pore

2. Collar:-  

• Short, cylindrical region behind the proboscis
• Contains the mouth on its ventral side
• Assists in locomotion and burrowing

3. Trunk:-  

Longest part of the body

Divided into three regions:

• Branchiogenital region: with gill slits and genital folds
  Hepatic region: with hepatic caeca
  Post-hepatic region: ends in a terminal anus

5.0Digestive System

The digestive system of Balanoglossus is straight, complete, and functionally specialized for filter feeding.

1. Mouth

Located ventrally between the collar and proboscis

Always open, leads to the buccal cavity

2. Buccal Cavity

Found within the collar region

Lined with cilia that transport food toward the pharynx

3. Pharynx

Located in the anterior trunk

Divided into:
Dorsal branchial portion: Contains multiple gill slits (filter feeding)
Ventral digestive portion: Forms the oesophagus

4. Oesophagus

A narrow continuation from the pharynx to the intestine

Conducts food posteriorly

5. Hepatic Caeca

Paired, sac-like outgrowths in the hepatic region of the trunk

Secret digestive enzymes

Aid in digestion and absorption

6. Intestine and Anus

Intestine runs posteriorly and ends in the terminal anus

• Site of digestion and absorption
• Waste is expelled through the anus

6.0Feeding Mechanism

Balanoglossus is a ciliary feeder:

• Cilia on the proboscis and gill slits create a water current
• Food particles stick to the mucus secreted by the proboscis
• The food-mucus mass is moved backward to the collar and then enters the buccal cavity
• Amylase and other digestive enzymes begin digestion
• Further digestion and absorption take place in the hepatic caeca and intestine

Mode of Digestion

• Digestion is extracellular, aided by enzymes like amylase
• Enzymes are secreted by proboscis, oesophagus, and hepatic caeca
• Absorption occurs in the intestinal wall
• Undigested waste is eliminated through the anus