Filter Feeding

The feeding behavior of an organism is the process of obtaining and consuming food. Every organism has an established feeding method, which helps them intake the required amount of nutrition and minerals for its survival and growth. Some of the feeding methods are deposit-feeding, fluid feeding, bulk feeding, ram feeding, suction feeding, and filter-feeding. 

In this article, we shall be discussing in detail one of the feeding methods which is Filter Feeding. By the end of the article, students shall be knowing the following -  

Table of Contents - 

• Filter Feeding - An introduction

• What is filter-feeding?

• Example of Filter Feeding Animals

• Types of Filter Feeders 

1. Internal Filter Feeders

2. External Filter Feeders

• Key learnings from the article

• Frequently asked questions

What is Filter Feeding?

In zoology, filter-feeding is a method of obtaining food in which food particles or microscopic creatures are randomly filtered from the water. Filter feeding is mostly found in small to medium-sized invertebrates, although it can also be seen in a few large vertebrates (e.g., flamingos, baleen whales).

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The gills of bivalves like the clam, which are larger than required for breathing, also serve to strain suspended particles from the water. Cilia, which are hairlike filaments, create a water stream across the gills, and other cilia carry trapped food particles over the gill face and into food grooves. Many bristle worms, such as the Sabella fan worm, have ciliated tentacles near their mouths that catch passing food particles. Certain crustaceans, such as the brine shrimp Artemia, have hairlike setae on their limbs that filter microscopic creatures as they swim.

The blue whale's teeth are replaced by baleen or whalebone. The shrimp-like krill ingested by the whale in a mouthful of water is trapped by these narrow vertical plates, which dangle inside the mouth cavity and are fringed on the inner edges.

Filter Feeding Animals

Clams, krill, sponges, baleen whales, and a variety of fish are among the filter-feeding animals (including some sharks). Some birds, such as flamingos and certain duck species, are filter feeders as well. Filter feeders play a vital role in water clarification and are hence classified as ecosystem engineers.

Types of Filter Feeders 

There are Two Types of Filter Feeders:

Internal Filter Feeders - Internal filter feeders have a basket-like filter inside a body cavity with two siphons that open to the outside. Water is brought in by one hole (the incurrent siphon), pumped through the filter to remove minute food particles, and then discharged via another opening (the excurrent siphon). Food particles are moved from the filter to the animal's mouth via mechanisms.

External Filter Feeders - All barnacles, both acorn and goose, as well as various types of polychaete worms, adopt this method. Barnacles are crustaceans that have been considerably changed, standing on their heads and sifting with their legs. Instead of pushing water over the filter, these animals utilize a grabbing motion, extending their feet upwards into the water in a rhythmic manner and then quickly bringing them back within the shell, along with any collected food.

The tube-dwelling polychaete worms, sometimes known as feather dusters, use a similar external but retractable filter. Some dwell in mucus and sand tubes, while others dwell in a harder, calcified tube. When challenged by low tide or predation, they can retract and close a door (operculum).

Filter Feeding in Mollusca

Filter feeding in molluscs feeds by filtering suspended debris and food particles from water using their gills. The majority of bivalves are filter feeders, as evidenced by their clearing rates. Environmental stress has been shown to affect bivalve eating through modifying animals' energy budgets, according to research.

Filter Feeding in Polychaetes 

The phylum Annelida is divided into four main classes, one of which is the Polychaeta class. Filter feeders include several sedentary and tubicolous polychaetes (such as Sabella). Polychaetes have long bipinnate filaments or tentacles called radides on their heads, with a ciliated groove running along their oral surface. Filter feeding in nereis diversicolor is used to gather food particles that have sunk to the bottom of a container of water.

Filter Feeding in Echinoderms 

All echinoderm species are found in the sea. Filter feeders that collect food particles filtered from seawater, deposit feeders that sift through sediments at the ocean's bottom to acquire food particles, predators, and scavengers are all examples of echinoderm eating.

Filter Feeding Mechanisms in the Sponges 

Sponges are inanimate, yet they have a water current system composed of canals and chambers that allow them to pump in water, filter food, and consume a large amount of it. The sponge gets water through a pore called the ostra. The meal is subsequently captured by collar cells as it moves through the system. The water is ejected from the sponge through an orifice known as the oscula.

Do You Know?

What do filter-feeding whales use to catch prey?

Filter feeders include blue and humpback whales, as well as other baleen whales. They take in large gulps of krill-infested saltwater, squeezing the water through their baleen, and swallowing their catch.

Key Learnings from the Chapter 

• Organisms adapt to different feeding methods depending on the differences in their living conditions and environment.

• In filter-feeding organisms, specialized filtering organs help them strain suspended particles and digestible matter from the water. 

• Filter feeders are of two types where internal filter feeders consume water from one pipe and flush it out from the other. 

• External feeders do not push the water into the filter and make a rhythmic motion to pick only the food from the water.