Lab Activity 4.1
Simple Invertebrates


Study the instructional material below. Be sure to click on each of the photographs for an enlarged view in a separate window. The larger version is necessary to complete the assignment. It opens in a separate window which can be resized by grabbing the bottom right corner and dragging it. It can also be moved by grabbing the top heading bar and dragging it. Be sure to close the extra window by using the X in IBM, or the close box in MAC when you are finished using them.


Marine invertebrates are animals without backbones that live in the sea. Over 97 percent of all animal species are invertebrates and the majority of these are marine. Thses species are divided into 33 phyla of which four phyla the Porifera (pore bearing animals), Cnidaria (stinging cell animals), Platyhelminthes (flatworms), and Nematoda (roundworms) will be featured in this lab activity. These phyla are considered simple invertebrates because they lack complex organ systems and specialized body cavities.

Top  Instruction

Examine the photographs of the invertebrates depicted below. Study the descriptions that go with each photograph and learn the stated information about the biology of each one.

Be sure to write about what you are learning in the lab section of your notebook. You will be expected to answer questions about the lab activity during the lab self test and lab quiz. It helps to have your text and coloring books open beside you for support.

Supporting Information
Refer to the Assigned Readings Below:
Marine Biology Textbook Chapter 7, pages 118 to 125
Marine Biology Coloring Book Plates 22 to 25
Phylum Porifera (pore bearing animals): Sponges
1. Water flows through the body of a sponge entering through many small pores called ostia and exiting out a larger opening called the osculum.

2. Sponges have a skeleton made up of many tiny skeletal elements called spicules.

3. The shapes of sponges are highly variable. Some grow flat and are called encrusting, while others form barrel shapes and are called tubular.

Phylum Cnidaria (sting cell animals): Hydroids, Jellyfish, Sea Anemones, and Corals
1. A sea anemone has the polyp basic body form. It's attached to the bottom with its pedal disc and its mouth and tentacles face up.

2. Reef-building corals are colonial. Each individual in the colony secretes a skeletal cup of stony calcium carbonate.

3. Both corals and anemones have tentacles that are covered with specialized cells which discharge nematocysts. These stinging cells are used in capturing prey and for defense.

4. The polyps of marine hydroids generally occur as colonies forming branched structures.

5. Individual polyps of Obelia are specialized for feeding or reproduction.

6. Hydroid colonies are either attached to the bottom as in Obelia or floating as in Physalia.

7. A jellyfish has the medusa basic body form. It swims freely with its mouth and tentacles facing downward.

8. Jellyfish have an umbrella shape with a mouth bearing manubrium hanging from the center.

9. The moon jelly Aurelia has a set of four oral arms which surround the mouth and are used to scrape food from the edges of its body.

Phylum Platyhelminthes (flatworms): Turbellarians, Flukes, and Tapeworms
1. The great majority of flatworms are marine living in sand or under rocks.

2. Flatworms locomote with a gliding motion by means of rippling muscles and beating cilia on their undersides.

3. Some flatworms, such as flukes and tapeworms, are parasitic living inside other animals.


Phylum Nematoda (roundworms): Roundworms
1. The typical nematode body is elongate, cylindrical, and tapered at both ends.

2. Tiny roundworms are present in prodigious numbers in marine muds where they feed mostly on bacteria and organic matter.


3. Many roundworm species are predators of marine plants and animals.

Lesson 4