Aquatic organisms are incredibly diverse. The following information is designed to give you a brief overview of some of the major groups of organisms that you will find as you study various aquatic systems during this class. It is not inclusive and, for the most part, uses common names for these organisms.

All living things are divided into large groups called Kingdoms. You are probably familiar with the plant kingdom and animal kingdom, for example. Each kingdom is further divided into groups called phyla for animals (phylum is the singular) and divisions for plants. Phylum or division is further divided into class, order, family, genus and species.

The major kingdoms in most systems of classification are the following:

A. Monera. These are simple, single-celled or colonial forms that do not have a membrane-bounded nucleus (prokaryotic). Important organisms in this group are the bacteria and the blue green bacteria (formerly known as the blue green algae).

B. Protista. Organisms in this kingdom are also single-celled or colonial but they have a distinct nucleus (Eukaryotic). Some of the organisms in this kingdom are plant-like (they carry out photosynthesis). We call these organisms algae. Diatoms are an example of an alga that is important in aquatic systems. Other organisms in this kingdom are more animal-like. We call these organisms protozoans. Different types of protozoans have different forms of locomotion. Some protozoans (ciliates) have cilia (small hair-like structures); others (flagellates) move by pseudopods -- the whole cell flows in the direction of movement.

C. Fungi. Fungi are unique organisms that are parasites or saprophytes (feed on dead organic matter). They may be single-celled or colonial, but most are multicellular (composed of many cells which have become specialized to carry out different functions within the organism). Most aquatic fungi are small and look like a mass of threads. Mushrooms are a type of fungus with which you are familiar.

D. Plant. Almost all plants are photosynthetic autotrophs (they are able to make their own food).

Most plants are multicellular although a few algae are included within this group, some of which are single-celled or colonial. The green algae are important in both fresh water and marine systems. The red algae and brown algae are large algae that are almost exclusively marine. Other plants at are found in aquatic situations are small plants like mosses and flowering plants such as water lilies and cattails.

E. Animal. This kingdom consists of multi-cellular organisms that cannot make their own food and depend directly or indirectly on plants. Most animals have fairly complex structure with specialized systems for movement, digestion, et c. Most also have nervous systems to help coordinate the organisms activities. A nimals tend to be divided into two basic types--vertebrates (animals with backbo nes) and invertebrates. The vertebrates include fish, amphibians, reptiles, bird s and mammals. You should see representatives of all these groups on your field trips.

There are many phyla of invertebrates. Some of the more common anim als that you are likely to see include the following:

1. Sponges (Phylum porifera).

These are simple organism which consist of an outer layer of cells and an inner layer which surrounds a network of internal pores and canals. These organisms are sessile (are attached to the substrate an d do not move). Most are marine although there are reshwater sponges in our loc al area. These sponges don't look like typical animals--most appear as a mass of cells attached to sticks or other structures in the water.

2. Hydra, Jellyfish and Sea Anemones (Phylum cnidaria).

These are simple organisms that float in the water (jellyfish types) or move sl owing along a subs trate (hydras and sea anemones). Most capture small organisms with their tentacl es which surround their mouths. You will see hydras in the lab and possibly in t he field. Corals are also members of this group.

3. Planarians (Phylum platyhelminthes).

Planarians are flatworms. They are common in streams in our area. They are smal l, usually dark brown or black, arro w-shaped organisms that glide along the undersurface of rocks by means of cilia on their lower surfaces. They have an esophagus and mouth on the middle of their undersides. They capture and consume small aquatic

organisms.

4. Segmented Worms and Leeches (Phylum annelida).

You are familiar with earthworms. You may find earthworms near the edges of streams or ponds. There are also aquatic species, including many marine forms. They typically have a long worm-like body which is divided into segments (block-like sections). The marine forms often have broad paddle-like extensions on each segment to help them absorb oxygen. Leeches are annelids that are external parasites. They attach to fish or other organisms and bite through the outer layers of cells to absorb blood and fluids from the host organism.

5. Snails, Clams, Oysters (Phylum mollusca).

Many of the organisms of this group have distinctive hard calcareous shells which cover and protect them. So me are sessile; others move slowly along surfaces or burrow into the bottom subs trate. Some mollusks such as slugs, octopus and squid do not have external shells. Note the diffident kinds of shells on the mollusks you observe on the field trips.

6. Insects and Crustraceans (Phylum arthropoda).

Organisms in this group have jointed legs and other appendages and hard jointed other skeletons called exoskeletons. In freshwater systems, two of the most common arthropods are insect s and crustaceans. Insects typically have six legs although some of the larval forms don't have any legs. Think of the caterpillars (larvae of butterflies), for example. Many insects are aquatic in their juvenile stages (larvae or nymphs), but emerge to form winged adults that can fly. Some insects continue to live in water as adults. You should see many different kinds of insect larvae on your field trips. We have some keys to help you identify these organisms.