Phylum Mollusca

Leucosolenia

Leucosolenia (A word of warning don’t fall into the trap of thinking that Leucosolenia is a leuconoid sponge because of the similarity between the genus name and the architectural type!) is an example of the asconoid architecture, one of the simplest found in the phylum. This also means that they are also the least efficient at trapping food from the water passing through them. It also limits their size, why?

Click for larger picture Fig. 1. The sponge Leucosolenia is colonial and appears to be nothing more than a mat of tissue.
BIODIDAC

These small, white, delicate sponges live in colonies with new individuals budding from the base and branches of the colony. Each member of the colony is connected to the next by hollow branches, extensions of the spongocoel. Leucosolenia is commonly found just below low tide levels and is anchored to just about any substrate it can hold onto.

Preserved materials

The branching nature of the colony results in dense mats making it difficult to distinguish one individual from the next and the preserved material looks nothing like the usual illustration of a leuconoid sponge. If you want to see the characteristic asconoid body plan you’ll have to use a fine pair of scissors to cut off a piece of the colony. Place it in a small petri dish with some tap water, and shake it gently in the dish to try and spread the tissue out. You can also try gently teasing it apart using a probe or needle.

Click for larger picture Fig. 2. Leucosolenia is an example of the simple asconoid architecture.
BIODIDAC

Do this while watching under the dissecting scope and you’ll be less likely to tear the sponge.

It will be hard to tell the difference between a torn sponge with its central spongocoel exposed and an osculum, but one difference between the two is the presence of tissue damage disrupting what would be the circular opening of the osculum. Whether you see the osculum in your specimen or not, the spongocoel should be visible along with perhaps some new budding individuals. Look closely at the body wall of the sponge and you’ll be able to see the outline of the spicules embedded there.

Asconoid sponges differ from the other two types of sponges in how water enters the sponge. A single porocyte surrounds each incurrent pore. In other sponge architectures s a series of cells forms the opening more appropriately called an incurrent pore, dermal pore or ostium.

Prepared slides

If you weren’t able to find the osculum, or porocyte in the preserved specimens be sure to take a look at the microscope slides with whole mounts of Leucosolenia. The spicules will also be easier to see in these stained specimens.

The cross-sections and longitudinal sections are also available and may, at first, be difficult to interpret. Remember that these are thin-walled animals with sharp calcareous spicules embedded in their body walls. As the microtome makes the thin tissue slices on your slide, the spicules shatter and tear the specimen. You’re best bet is to work your way around the perimeter of the section as you make your observations of the different cell types. You’ll have to be sure that you light source is properly aligned, and oil immersion will be advantageous as well. As you look at these slides identify the location of the choanocytes and their flagella. Depending on the quality of the slide, and how well you’ve set up your microscope, you may also be able to see the collar of these unique sponge cells. Can you identify the spongocoel or see any other types of cells? Be ready to compare this cross-section with that of Grantia (Scypha) in the next part of the lab.


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