Spectrum Biology - September 2016

 The detached vacuole undergoes acidic and alkaline digestion and the waste

vacuole moves to the cytophage (anus) for excretion.

Diversity in Digestive Systems of Some Invertebrates

Coelenterates Cnidarian (Hydra) has a

gastrovascular cavity. It has

a single opening, (mouth), which serves as the

entry and exist point for food and waste.

Extracellular digestion occurs in the

gastrovascular cavity, while intracellular

digestion occurs inside the food vacuoles.

Food vacuoles are formed when phagocytic

cells engulf food particles.

Platyhelmithes The gastrovascular cavity

in platyhelmithes (Planaria) branches

extensively. It is also an incomplete digestive

tract with only one opening. When a

planarian feeds, it sticks its muscular

pharynx out of its mouth and sucks in food.

Nematode A nematode (Ascaris) has a

complete digestive tract but less

differentiated with a mouth, pharynx and

anus.

Annelida The alimentary canal of Annelids

(Pheretima) is complete and well

differentiated. It runs from the anterior most

segment of the body till the posterior most

segment of the body right from mouth to

anus. The canal is differentiated into six

parts namely buccal chamber, pharynx,

oesophagus, gizzard, stomach and intestine.

Arthropods (Insects)

Here we will discuss about

grasshopper as a representative

insect, who has a complete

digestive tract and shows

extracellular digestion. During

the entire feeding process the

nervous system and the presence of

food exert considerable control over

enzyme production at various points

in the digestive tract.

Lips about mouth

Pharynx

Cut body wall

Lateral cord

Intestine

Rectum

Ascaris

Planaria

Eye

Anterior branch

of intestine

Intestinal

diverticula

Muscular

pharynx

Pharyngeal

sheath

Opening of

pharynx

Mouth

Lateral posterior

branches of intestine

Mouth

Food

Wastes

Tentacles

with nematocysts

Gland cell

Pseudopodia

Food particle

Food vacuole

Cnidarian (Hydra)

Gastrovascular

cavity

Food

Buccal cavity

Cytostome

1 Food vacuole forming at cytopharynx

2 Excess water leaves food vacuole

3 Lysosomes delivering enzymes to food vacuole

4 Food particles undergoing digestion in vacuole

5 Residual vacuole

Cytophage

6 Waste from vacuole

pH acid

pH alkaline

pH alkaline

Intracellular digestion in

a ciliated protozoan

Mouth Earthwarm (Pheretima)

Setae

Ganglion

Nerve cord

Seminal receptacle

Seminal vesicle

Ovary

Sperm duct Nephridium

Coelom

Muscle payer

Septum

Blood vessels

Gizzard Intestine

CesophagusCrop

Hearts

Pharnyx

Brain

Mastication of food by

mandibles and maxillae

Salivary

glands

Mouth

Oesophagus

Carbohydrases, lipases,

proteases by midgut

Crop

Return to

Stomach

Small food particles

Gastric caeca

(extracellular digestion)

Intestine

(absorption)

Rectum

(H O and ion reabsorption) 2

Anus

(solid faecal pellets)

Amylase

(carbohydrate

digestion)

Saliva

Large food particles

Oesophagus

Mandible

Maxilla

Palp

Labium

The adult grasshopper, showing the mouthparts

Position

of labrum

The food processing organs of the grasshoppe

Oesophagus Gizzard Midgut Hindgut

Salivary

glands

Crop Gastric

caeca

Excretory

tubule

Rectum