Question

) Mollusks use a variety of different feeding/digestive strategies depending on the class. For the classes gatropoda and bivalvia:

i) provide the path of food through each animal using a simple flow chart (x-> y -> z) containing all relevant structures or parts

ii) explain in one or two sentences why this difference in feeding strategies makes sense for the lifestyles of the two classes

iii) What are the primary differences between the digestion of mollusks and the digestion of arthropods?

iv) Compare the feeding behavior of the bivalves, cephalopods, gastropods, and chitons.

Answer 1

i)

GASTROPOD PATH OF FOOD

mouth( with radula, pharynx and salivary glands)------> esophagus------> stomach (called gastric pouch), with peristalsis (surrounded by digestive glands called hepatopancreas)-----> intestine -------> rectum--------> anal pore

BIVALVIA PATH OF FOOD

gills filter into body -------> esophagus-------> stomach with digestive glands------> intestine ---> rectum -----> anal pore

ii)

Gastropods include snails and slugs. They have got jaws to hold food in place while radula works on it. Salivary gland is well developed in predatory gastropod and help in digestion and lubrication. In herbivores stomach is developed into gizzard helping to grind food. Hepetopancreas secrete enzymes for digestion. Intestine helps to reabsorb water.

Bivalvia include marine and freshwater mollusk. So they are filter feeders. They filter water through body. This is adaptive for their sedentary lifestyle. Gills help in feeding and breathing.

iii)

DIGESTION IN MOLLUSK AND ARTHROPOD

a) arthropods have complete digestive system

b) mouth is well developed with appendages in arthropods

c) developed into fore gut, mid gut and hind gut in arthropods

d) foregut ends with crop and gizzard

iv)

Bivalvia are filter feeders. They filter water through gills and feed through mouth after proper selection of edible matter.

For feeding, gastropods has got radula, a hard plate with teeth. They have vivid feeding habits. They graze, browse, or scavenge.

Cephalopods catch prey with tentacles, draw into mouth and feed as bites. Most have radula.

Chitons feed by scraping food off rock with radula.