1. For swallowing inactive food:
Burrowing animals such as Lumbricus and Arenicola, generally feed on the organic matters present in the mud.
Image Source: veomed.com
They use their eversible pharynx for swallowing mud whereas crustaceans such as Upogebia and Callianassa, on the other hand use their mouth appendages for swallowing mud. The organic matters of the mud are utilized and the residue is ejected as faeces.
2. For scraping and boring:
ADVERTISEMENTS:
Some animals possess structures for scraping and boring of the food stuffs. Examples are Aristotle’s lantern of echinoids, radular apparatus of some molluscs, boring valve of Teredo and heavy mouth parts of termites.
3. For seizing the prey:
Some animals possess specialized organs by which they are able to seize the prey.
Yonge, as these organs are sometimes masticatory and digestive in function, classified these specialized organs into three following heads:
(a) For seizing only:
ADVERTISEMENTS:
Impaling proboscis of Didinium, nema- tocysts of coelenterate tentacles, the turbellarian pharynx, jawed pharynx of many polychaetes, teeth and radulas of some gastropods are referred to be the best seizing organs of the animals.
(b) For seizing and masticating:
Toothed jaws of vertebrates, jaws and radulas of molluscs, the jaws and other mouth parts of crustaceans, insects, arachnids and myriapods are the organs which are used for seizing the prey and are also masticatory in function.
(c) For seizing followed by external digestion:
ADVERTISEMENTS:
This type of feeding mechanism is found in starfish which uses its tube feet to force open its shell and simultaneously its stomach is everted for digesting the muscular part of the prey.
Some carnivorous gastropods, cephalopods and spiders seize prey with the help of cephalic appendages and also carry out some external digestion.