PHYLUM PORIFERA
The phylum Porifera (“to bear pores”) includes the sponges, a group of animals
believed in the past to be plants because of their sedentary nature. Structurally, the
sponge body is perforated by pores through which water is “pumped” by the action of
special flagellated collar cells known as choanocytes. Because sponges lack tissues and
organs, they are considered an early offshoot of animal evolution and are not closely
related to the other animal phyla.
Morphologically sponges exhibit a series of increasingly complex internal canal
systems. Three canal systems are recognized as follows: asconoid, syconoid and
leuconoid. Your textbook illustrates and describes these canal systems.
Class Calcarea
The calcareous sponges possess a skeleton consisting of many small, crystal-like
calcium carbonate (CaCO3) spicules embedded in a jelly-like matrix. Two common
calcareous sponges are Leucosolenia, a colonial freshwater sponge with an asconoid
body plan, and Grantia ( formerly Sycon or Scypha), also a freshwater species, displays
a more complex syconoid canal system.
Figure 1. Draw from a prepared slide a Leucosolenia sponge 7 centimeters (cm)
long. Label all structures.
Figure 2. Draw a Grantia sponge 7 cm long and label all structures.
Figure 3. Draw either a longitudinal section or a cross-section (X-S or C-S) of a
Grantia sponge 7 cm long. Label all structures.
Class Hexactinellida
These are the glass sponges. Spicules in this class are made of silicon dioxide (SiO2) or
glass and are tri-axon (3-pointed) or hex-axon (6-pointed). The spicules are fused into an
intricate, white skeleton of exquisite beauty. Glass sponges are usually deep-water,
tropical forms, common in eastern Pacific waters between 450 and 900 meters (m).
Some occur at depths of over 3 miles.
Figure 4. Draw a 5 cm by 5 cm portion of the skeleton of Euplectella (the Venus
Flower Basket sponge) showing the intricate network of spicules.
Class Demospongia
This groups contains the greatest number of sponge species and includes the majority of
sponges found in North America. Most species are marine. The spicules are composed
of silicon and / or spongin, a protein. Members of this group include bath sponges,
boring sponges and large urn-shaped sponges, sometimes measuring a meter across. All
demospongia are leuconoid.
Due to the tremendous amount of shape variation in living sponges, spicules are used
for identification. Chlorox can dissolve away sponge tissue revealing spicules composed
of silicon dioxide, these can be studied with the light microscope.
Figure 5. Draw three different types of spicules each 3 cm long. Obtain the
spicules from prepared slides.
Study Questions
1.
2.
3.
4.
How many layers of cells are present in sponges?
What advantages do sponges have over the Protists studied in lab?
What disadvantages do sponges have when compared to Protists?
From what group of Protista do scientists think sponges evolve from?
Why?
5. What structures keep the water moving through the wall of a sponge?
6. How do sponges reproduce?
7. How do sponges get oxygen to their cells?
8. How do sponges get rid of their wastes?
9. Why are the larger sponges a maze of passageways instead of being
hollow like a simple asconoid sponge?
10. How does a sponge get food to its cells?
Figures