This chapter is our introduction to the Animal Kingdom. In order to look at the characteristics of large animals we must first understand the origin of the smaller and most simple animal organisms. This chapter will allow us to look at how sexual reproduction has allowed animals to change over our long existance on the planet and yet we can see how simple some of these invertebrates are and why asexual reproduction is still possible. This study will include the sponges in the phylum Porifera, the jellyfish in the phylum Cnidaria and the flatworms in the phylum Platyhelminthes and the roundworms in the phylum Nematoda.
 
 

    Sponges belong to the phylum Porifera ( pore bearing) or which means they are made up of many pores. There are many small openings called pores on the sidewall of the sponge, which allows for these organism to take in water and filter the nutrient material out of the water. Sponges are called sessile ( stationary or in one spot) filter feeders due to the fact they stay in one spot all their lives and filter the water for nutrients as it passes through their body.

    A sponge has the basic structure of a bag, a large internal cavity with an opening at the top.There are several different types of cells and structures that make up the sponge. The structures that you should be familiar with are described below.

    Osculum- this is an opening at the top of the sponge which helps control the flow of water through the sponge cavity. If the  osculum is open the flow of water will come through the sponge. If it is closed no water will flow through the sponge.

    Choanocytes- Commonly called collar cells are have a spherical shape with a collar at one end, and has a flagella sticking out ot the collar. As the flagella moves, this helps draw water into the sponge through the pores in the sidewalls and traps food material out of the water.

    Amebocytes- These are irregular shaped cells which function to carry nutrient material from the choanocytes to all cells within the sponge, these cells also carry away waste meterials.

    Mesenchyme- a jellylike middle layer of the sponge body

    Spongin- is a resiliant, flexible protein fiber material which produces the internal framework for the sponge.

    Spicules- are little spike like structurs often resembling the jacks used in childrens games.These structures give the sponge a more brittle support framework. These spicules are made of either two materials, calcium carbondate or silica and are often embedded into the spongin. Taxonimist classify sponges according to the materials that make them up into three classes.

    Asexual - There are a couple different forms of asexual reproduction that occur within various types of sponges. Remember that asexual reproduction produces exact copies unless a mutation of the genetic code would occur.

                          Regeneration- By taking a sponge and breaking it into peices, one could cause each peice of the sponge to develop into an adult sponge just like the parent, this is regeneration.
                          Gemmules- are clusters of amoebocytes, and other cells  making up the adult sponge and  encasing these cells and ample food in a protective covering, to allow them to with-stand cold waters or dry environments. When conditions become favorable again the gemmule will develop into a nedw sponge.

    Sexual Reproduction- Sponges are hermaphrodites, which means they have the ability to produce both egg and sperm. To ensure that self fertiliztion does not occur, they release sperm at different times than they would produce their own eggs.

Calcareous Sponges- have spicules composed of calcium carbonate.

Hexatinellida- "the glass" sponge has spicules of silica

Demospongia- Have skeletons made of silica, spongin or both. 80% of all sponges belong to the class demospongia.
 

    Whatever their shape or size, all sponges have two things in common; they have a body wall penetrated by many pores, and they are all sessile (attatched to one spot or don't move).

Introduction to the Porifera

Sponge Systematics

Sponges

Introduction to the Cnidaria

     All Cnidarians are more complex than the sponges or phylum porifera. All Cnidarians have a gollow gut with a single opening and flexible, fingerlike tentacles. On the tentacles are stinging cells called cnidocytes, which contain a harpoon-like nematocyst.
    Cnidarians are found in two very different types of body forms.
        Polyps- which are vase shaped bodies.
        Medusa- which is a umbrella shape to its body plan.
    Classification on the cnidarians occurs due to there life cycle and what type of body plan they express. Presently we will be looking at 3 classes of cnidarians; the Hydrozoas, Scyphozoa and Anthozoa organisms.

Class Hydrozoa- These organisms spend part of their life as medusae and part as polyps during their life cycle. Most are colonial marine organisms with both polyp and medusae stages to their life cycle. The one freshwater hydrozoan we are familiar with is the Hydra. This freshwater organism is unique to this  class because they have no medusa state and only exist as a polyp.
    Basal Disk- this is a region of the hydra or other polyp forms which secretes a sticky substance that allows it to attatch to rock and other materials where it live.
    Movement- Hydras can glide around by decreasing the stickiness of the secreation, or they can form a bubble filled with gas at the basal disk area in which they float in the water to new locations. They also have a form of movement which resembles tumbling which is illistrated on pg. 643 of the text.
    Portuguese man of war- is a marine organism found in this class, some tentacles may get as long as 50 ft.
    Reproduction- Normally the polyp forms reproduce asexually by forming small buds, this process is called budding. They may also reproduce sexually in the medusa stage. Males will secrete sperm in the water and the females will secrete eggs. Apon fertiliztion the eggs will develop into a Planulae, which is a free-swimming larval form that may take the cnidarians to a new, richer environment.

Scyhphozoans- These may be the best know cnidarians due to the fact that this class contains the jellyfish. Scypha means cup and zoans referrs to animals. These organsism spend most of their time as medusae forms. They do go through a small unnoticed polyp phase during their life cycel.
 

Phylum Cnidaria
Cnidarians and Ctenophores
The JellyFish Page

The class Anthozoans is the largest class of cnidarians. Anthos means flower which comes from the crown of tentacles that occur on the superior portion of their body. They typically have a stalklike body topped by a crown of tentacles that occur in groups of six. No medusa stage occurs in this class. Two representative examples are the sea anemones and the corals.

Sea Anemones- are soft-bodied polyps found all over the world.They feed on fish and other marine life. They are highly muscular and relatively complex with internal cavities.

Corals- Most live in colonies. Each polyp secretes a tough stone-like outer skeleton made of calcium rich material. When a poly dies its skeleton remains which develops the coral reefs we know of today.  A coral reef provides shelter and food for an enormous amount of marine life. There are basically 3 types of coral reefs we have discussed.

    Fringing Reefs- Fringing reefs form close to the shore line or beach. These reefs usuallly have a symbiotic relationship with photosynthetic organism.

    Barrier Reefs- form in much deeper waters. The Great Barrier Reef, off the coast of eastern Australia, is the largest in the world and can be viewed from outer space.

    Atolls- form even farther out from land masses. These reefs form in a ring shape with a lagoon in the center. Darwin said these reefs formed around mountains or volcanoes which were sinking into the ocean at the same rate the reef was growing upward, this kept the corals living zone near the surface of the water.
 

    The remaining phyla of simple invertebrates have tubular bodies. Most are what we call worms. These organisms are a lot more complex than the sponges and cnidarians. The 4 phylas are listed and described below.
 

Phylum Platyhelminthes- The flatworms, are bilaterally symmetrical, with simple bodies that lack respiratory and circulatory systems. A flatworms body is solid and has no body cavity, so they are called Acoelomates.There are 3 major classes of flatworms.

    Turbellaria- This group of flatworms are mostly marine, freeliving organisms. The exception to this group is the planarian Dugesia. The planarians rear is tapered while its front end is round like a shovel.

Tremetoda- The Flukes- This is the largest flatworm class. Some flukes are endoparasites ( live inside the host) , others are ectoparasites ( live outside the host). Endoparasites have a special outer covering called a tegument, which protects them from being digested by the host. Most flukes have a complex life cycle.

    Life Cycle of the fluke which involves the human and snail is described on pg 649, you should be familair with this cycle.

    Cestoda- The Tapeworms.Tapeworms have a special head called a scolex which has suckers and hooks to remain attatched to the intestinal wall of the host. Tapeworms may grow up to 12m  long- 40 ft. We gain access to tapeworm by eating undercooked beef. The larvae is in the meat, if we properly cook or freeze the meat we will kill the parasite.

Phylum Rhynchocoela- Commonly called the ribbon worms, are much larger than the platyhelminthes group. They usually grow from 1m in length to 30m in length, and they are also a marine group. This group also has an acoelomate body plan.
    Proboscis- is a special muscular tube that they quickly thrust out to capture prey with.

Phylum Nematoda- These are the roundworms and are characterized by the presence of a pseudocoelom body plan. The false body cavity is formed in between the endoderm and mesoderm germ layer.
    Ascaris  is one of the more common roundworms that affect humans and animals. The life cycle is on page 652, which you should be familiar with.
    Necator- This group of worms are small enough to bore holes in the bottom of your feet and the larvae are found in the soil in warm tropical soiled climates. These worms consume blood cells, causing anemia.
    Trichinella- This is a worm which is found in pork. We have basically eliminated the disease Trichinosis due to properly cooking and freezing pork and raising the hogs in more hygenic conditions.

Nematoda Worksheet

Ringworms, Roundworms and hookworms

Prevention of Roundworm and Hookworms

Phylum Rotifera- This phylum is characterized by having cilia line the mouth cavity. As the cilia move, they take on the appearance of a rotating wheel. This process moves food into the mouth area. These organisms consume bacteria and protist organism. They have a pseudocoelom and a one way gut.
 
 

Chapter 28 Review Sheet