There are four methods of feeding: grazing, hunting, scavenging and filtering.

Graziers

Grazers are herbivores who eat plants like seaweed and algae. They don't eat any meat.

Limpets are grazers who lick the algae using their specially adapted tongues, called raspers.
The limpets tongue is very rough and leaves scars
on the rocks where they have been grazing.

Sea urchins have a circular mouth with five sharp teeth which they use to bite and chew the seaweed. This is called Aristotle's Lantern. Which is on the underside of the sea urchin, known as the test, (the sea urchins are a little mixed up compared to us humans as its mouth is underneath and its bottom is on top! picture

Hunting

Sea anemones, dog whelks and crabs are some of the top predators of the beach, but they all have adapted differently to prey on their next meal.
Anemones are not plants but preditory animals that can move if conditions become unfavourable, but normaly static. If any small fish, prawn or smaller organism passes closely and lightly brushes the tenticles, they are triggered and fire a coiled filament into the prey, poison is injected and the prey is paralised. The prey is then passed by the tenticles to the anemones mouth, which is in the centre of the column. Its swalled, digested and the waste products are expelled.
Many people are allergic to the stings, so take care!

Dog whelks eat other sea snails and barnacles. They secrete digestive juices which soften the shells so it can drill into it. More juices are injected , which turns its preys body to mush. The dog whelk then sucks this up!
The whole process can take 14 hours!

SCAVENGING

Scavengers ( detritivores ) feed on dead plants and animals (detritus ).
This is so important as they are the cleaners of the sea and without them all the waste will build up and up, poisoning the sea.
Prawns, shore crabs and brittle stars are all scavengers.

Prawns sense what is detritus
Brittle stars mostly eat organise detris on the sea floor. They have a very simple stomach and all the waste material is passed back out of the mouth picture

FILTERING

Filter feeders live off the plankton that is suspended in the sea.
Filter feeders include sea squirts, sponges, barnacles and hairy mitten crabs.

Sea squirts use two siphons one for the intake of water, containing the plankton, and one which is used to get rid of the waste. The bodies contain an intestine system which absorbs the plankton. They also have a different blood circulation system to other animals as the blood is pumped one way around the body, then the blood flow is reverse so it flows around the sea squirt in the opposite direction, both flows happen for the same amount of time, about a few seconds.