Porifera: Body Plan, Symmetry & Skeleton

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  • 0:01 Porifera
  • 0:45 Asconoid
  • 1:47 Syconoid
  • 2:41 Leuconoid
  • 3:26 Not a Bone in Their Body
  • 4:44 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
In this lesson we'll explore the varied types of body plans that porifera utilize and take a look at some of their more universal features, such as their body symmetry and their 'skeletal' support structure.

The Not-So-Square Pants of Porifera

If you watch a lot of cartoons, then you probably know about SpongeBob SquarePants, a square-shaped sponge who lives in a pineapple under the sea. He's not real, of course, but actual sponge organisms do exist in the animal kingdom. They are called porifera, and they live in marine environments (sadly, without any pants).

Now, you may be familiar with the fact that sponges come in a variety of colors and shapes and sizes, but did you know that, among that varied world of dazzling colors and wonky shapes, there is actually a great deal of uniformity in their body plan? Well, watch on, because we are about to explore what it means to have an asconoid, syconoid, or a leuconoid body plan.

Asconoid

The most simplistic body plan within the phylum porifera is the asconoid body plan. This is such a simplistic structure because the body plan has only one large internal chamber, called a spongocoel, that is lined with water-filtering choanocyte cells. Choanocytes are responsible for feeding the sponge by filtering organic materials out of the water. They also create the internal current that keeps water from becoming stagnant within their spongocoel.

Now, as a consequence of this body plan, the tissue of asconoid sponges is thinner than that of the syconoid or leuconoid, as their goal is to get the nutrient-carrying water to the filtering choanocytes as quickly as possible. Sponges of this body plan are smaller in size because their thin tissue is more breakable and can't readily support large structures. Some examples of this body plan are the yellow tube sponge and the purple vase sponge.

Ok, so now that we've looked at the most basic body plan, let's go on to explore how the asconoid shape is different than the syconoid shape.

Syconoid

The main difference between asconoid and syconoid body plans is that syconoid sponges have a row of tiny chambers, called radial canals, within their tissue that house their choanocytes. Now, this may seem like a minor difference, but it results in two major advantages: additional girth and increased surface area for feeding.

So, why are additional girth and increased surface area a big improvement? Well, increased girth means that their body walls are thicker and, as a result, have a greater capacity to support a larger overall body size than an asconoid. Furthermore, the additional surface area added by the many radial canals means that more of that water makes contact with those little filtering choanocytes. Thus, more nutrients are gathered to grow a larger body form.

Ok, so now that we've looked at the asconoid and syconoid body plans, let's look at the pièce de résistance of the leuconoid body plan.

Leuconoid

The leuconoid body plan belongs to the big boys of the porifera world. These sponges, like the syconoid, also have radial canals but, unlike syconoids, leuconoids have more than a single row of these canals. If you were to cut a cross-section of a leuconoid sponge you would see a dense network of radial canals, meaning that leuconoids are superior in their capacity to filter more nutrients and, in doing so, are able to grow to be the largest of the sponges, due to their structurally thick and supportive body walls. In fact, leuconoid sponges are referred to as the 'red-woods of the reef' because they're some of the oldest and largest sponges, with some growing to about 8 feet in diameter and estimated at over 2,000 years old.

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