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In this lesson, we will explore the phylum Porifera and look at the organisms that make up the group. We will discuss their key features, body structure, their filtration mechanism, and why they are so important to the oceans.

Porifera Defined

Ok, so everyone probably knows who SpongeBob SquarePants is, right? Well, did you know that he could also be known as PoriferaBob SquarePants? Why, you ask? Well, the term Porifera is actually the scientific name given to the group of organisms known commonly as sponges. But, unlike SpongeBob, living sponges are neither square in shape nor in interest- they are actually a really important and diverse phylum within the animal kingdom. That’s right, sponges are actually living animals and we are going to learn a bit about them here.Porifera are exclusively aquatic animals.

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They are found in both fresh and salt water, and in shallow or deep water. Sponges come in all shapes, sizes, and colors. They can be cylindrical in shape, like the yellow tube sponge Aplysina fistularis, wide-mouthed and triangular, like the purple vase sponge Niphates digitalis, sheet-like and encrusting, like the red Spiratrella coccinea, or long and rope-like, like the grey species of Callyspongia.So, with all this diversity, what makes a sponge a sponge? Well, Porifera of all species have a skeleton composed of fine mesh of little needle-like structures, called spicules, that support the cells of the organism, as well as specialized filtering cells, called choanocytes. But, before we jump into these key features, lets take a moment to understand the body plan of Porifera.

Body Structure

A sponge, being a filter-feeding animal, has thousands of little pores and canals running through its body.

Water is drawn in and shunted throughout its tissue for filtration. In fact, the vast number of pores in a sponge’s body are actually where the phylum derives its name from; Porifera literally means ‘bearing pores.’The most abundant pores, called ostia, are used to draw water into the animal’s interior cavity, called the spongocoel. Other cells, such as the osculum are exit pores that expel filtered water out of the organism. Once water passes through the ostia, and into the organism, it usually enters a series of canals that connect little chambers within the tissue, called radial canals. The surface of these canals is lined with specialized cells, called choanocytes, whose sole purpose is to filter any organic particulate out of the water for feeding or, if the season is right, to filter eggs and sperm out of the water during reproductive spawning events.

Choanocytes ; Spicules

If you were to cut a cross section of a sponge and look under a high powered microscope, you would see many different types of cells that are equally important to the life cycle of the organism. However, here we will focus on the key features of Porifera: choanocytes and spiculesChoanocytes, also known as collar cells, derive their name from the collar-like base where the flagellum (or tail) protrudes. These tails wave back and forth not only to create a current, pushing water along so that it doesn’t stagnate, but also to collect particulate into the collar of the cell, which funnels it into the body of the collar cells, where it is drawn into the tissue for consumption.Sclerocytes are the cells responsible for forming the structural supports of the sponge, known as spicules. They come in a variety of shapes and the basis of their composition is what further divides the phylum into three classes of sponges. Demospongia is the largest class of sponge and has spicules composed of spongy protein called spongin and crystalline silica. Calcarea have rigid spicules composed of calcium carbonate.

Hexactinellida, a rare class found mostly at great depths, have completely salacious spicules and so are also known as ‘glass sponges.’


So why are sponges so important? Well, they compose over 90% of the benthic (meaning ground dwelling) organism in the ocean and some, like the barrel sponge, can get as big as six feet in diameter. So, with all of that sponge biomass, that means that there is a LOT of filtration going on.

In other words, sponges are one of the most efficient natural filtration systems for digesting, and thus ridding the oceans of bacteria and other organic debris. Some sponges are capable of filtering as much as 260 gallons of water per two pounds of tissue!

Lesson Summary

Let’s review! Porifera are ‘pore bearing’ organisms, commonly known as sponges, that come in all shapes, sizes, and colors. They are found in both fresh and salt-water environments, and in shallow or deep waters. The main features of their body include a skeleton composed of a fine mesh of needle-like spicules, which support the cells of the organism, and specialized filtering cells called choanocytes.Porifera are divided into three main classes based on the composition of their spicules. Demospongia, the largest class of sponge, have spicules of spongy protein.

Calcarea have rigid spicules composed of calcium carbonate. Hexactinellida, a rare class found at great depths, have completely salacious spicules and so are also known as ‘glass sponges’.

Note on Phylum Porifera

Sponges, or porifera, are aquatic invertebrates
*Porifera is the scientific name for sponges *Found at any depth of fresh and salt water *Includes three main classes: Demospongia, Calcarea, and Hexactinellida *Share two main features: skeleton composed of spicules and specialized filtering cells called choanocytes

Learning Outcomes

After you’ve reviewed this lesson, you should be able to:

  • Describe phylum Porifera
  • Identify the three main classes of Porifera
  • Describe the body structure of sponges
  • Recall the important role Porifera play in the environment

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