Phylum Porifera: Definition, Characteristics & Examples

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  • 0:01 Porifera Defined
  • 1:35 Body Structure
  • 2:40 Choanocytes and Spicules
  • 4:02 Filtration
  • 4:39 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
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. 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 spicules

Choanocytes, 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.

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