Kingdom Animalia

• Phylum Porifera

• Phylum Cnidaria
  • Class Hydrozoa
  • Class Anthozoa
  • Class Scyphozoa

Kingdom Animalia

Phylum Porifera
(Canadian Campbell 2nd Ed Concept 33.1)

Sponges are sedentary suspension feeders, which may be considered as simple multicellular animals. In general, water is drawn through pores into a central cavity called the spongocoel and then flows out a single, larger opening termed the osculum. The current is generated by the beating of flagella on specialized cells termed choanocytes, which line the spongocoel. These cells capture food particles suspended in the water that passes through their body. Most sponges are marine, however, a few freshwater forms do exist.

View the preserved sponges of the genus Grantia

Consider these questions:

• What is the body plan of a sponge?
• How does a sponge obtain nutrients?
• Is digestion in a sponge extracellular or intracellular?

Phylum Cnidaria
(Canadian Campbell 2nd ed Concept 33.2)

This Phylum consists of a large and diverse group of aquatic animals which are mostly marine in nature. Sea anemones, jelly fish, corals and the familiar fresh water Hydra all belong to this phylum. All cnidarians are basically radially symmetrical organisms bearing tentacles. There are two variations on the basic body plan of this phylum. One type is sessile and is known as a polyp. Polyps are cylindrical and adhere to the substratum via their aboral end, with their tentacles enxtended into the water column waiting for prey. The other type is the free-swimming medusa. This is the body form characteristic of sea jellies. In many cases the polyp form alternates with the medusa form in the course of the animal's life cycle.

Class Hydrozoa

Fresh water Hydra is commonly studied as a representative of this group.

• Examine a budding Hydra with a dissecting microscope
• Examine a slide showing Hydra in X.S.
• Examine a slide showing Hydra in L.S.

Take note that the basic form for Hydra is the polyp. Also notice that the cnidarian body wall is composed of two cellular layers with a layer of non-cellular material in between (note: the non-cellular layer is not equivalent to mesoderm). Sketch and label the cross section.

Consider the following questions:

• Name the three body layers.
• How does the Hydra feed?
• Is digestion extracellular or intracellular?
• What is the gastrovascular cavity?

Take note that Hydra is merely a representative of the class hydrozoa, and not all members of the group appear exactly the same. Prime examples of this variation are the colonial polyps of both Plumularia and Obelia, as well as the free-swimming Portuguese man-of-war (medusa).

Class Anthozoa

The class anthozoa includes the sea anemones and corals. For anthozoans, the dominant stage in the life cycle is the polyp.

Examine the preserved sea anemone and note the generalized form of a polyp. This is the stage characteristically seen attached to the substrate in marine environments.

Coral animals secrete hard exoskeletons of calcium carbonate, with each polyp generation building on the skeletal remains of their predecessors. It is these skeletons that we refer to as coral. Coral reefs are colonial forms which are high in species richness, due to their suitability as habitats for numerous invertebrates and fish.

Examine the preserved Deerhorn Coral from your lab

Class Scyphozoa

The class scyphozoa illustrates a group of cnidarians in which the medusa is the conspicious stage in the life cycle. Members of this class may have a polyp stage in their life cycle, but generally spend most of their lives feeding on plankton in the water column.

Examine the preserved jelly fish Aurelia