The Kingdom Animalia is a large group that consists of eukaryotic, multicellular organisms that are heterotrophic in nature. As such, they obtain their nutrition from external sources. Although they are unable to produce their own food, which is one of the main defining characteristics of plants, animal cells lack a cell wall that is present in plant cells.
Animal kingdom is divided into two:
Invertebrate & Vertebrata
These are animal without backbone and internal skeletons. It is also divided into:
The Porifera may be seen as an asymmetrical or radially symmetrical multicellular organism with a cellular grade of an organization without well- definite tissues and organs; exclusively aquatic; mostly marine, sedentary, solitary or conical animals with body perforated by pores, canals, and cambers through which water flows; with one or more internal cavities lined with choanocytes; and with a characteristic skeleton made of calcareous spicules, siliceous spicules or horny fibers of spongin.
CHARACTERISTICS OF PORIFERA:
- 1. They are simple aquatic invertebrates.
- 2. They do not move about but are attached to rocks or shells.
- 3. They live in colonies.
- 4. Their larval (young) stage is usually motile.
- 5. They are primitive multicellular animal.
An example of animal in this group is the sponges.
Coelenterate can be view as an aquatic invertebrate animal of a phylum that includes jellyfishes, corals, and sea anemones. They typically have a tube- or cup-shaped body with a single opening ringed with tentacles that bear stinging cells (nematocysts).
CHARACTERISTICS OF COELENTERATE:
- 1. They are multicellular organisms.
- 2. The body is made up of two layers.
- 3. They are mainly aquatic organisms.
- 4. Their bodies possess radial symmetry.
- 5. They reproduce asexually by Budding.
Example are: Jelly-fish, Hydra, Sea Anemones and Coral.
Phylum Nematoda is a phylum of an invertebrate animals. They are comprised of roundworms (or nematodes). They are identifiable by their smooth and tough outer covering and narrow cylindrical unsegmented body.
CHARACTERISTICS OF NEMATODA:
- 1. They have round body and cylindrical bodies.
- 2. They lack body cavity i.e. they have pseudo-coelom body cavity.
- 3. They are bilaterall y bisymmetrical.
- 4. Some are parasite s in animals while others are free living.
- 5. Some are hermaphrodite while others produce sexually.
Examples are: Roundworms, Hookworms, Guinea worms, Thread worms.
Annelids are defined as triploblastic, bilaterally symmetrical, metamerically segmented, a coelomate worm with a thin flexible cuticle around the body.
CHARACTERISTICS OF AN ANNELIDA:
- 1. They have internal and external segmented bodies.
- 2. The body is long and cylindrical.
- 3. They have a true body cavity or coelom.
- 4. Some are aquatic while others are terrestrial i.e. they live in the soil.
- 5. The alimentary canal has two opening the Mouth and Anus.
- 6. Annelids reproduce sexually and many are hermaphrodites.
Example are: Earthworm leeches and Tube worms.
Phylum Mollusca is the predominant phylum in marine environments. It is estimated that 23 percent of all known marine species are mollusks; there are over 75,000 described species, making them the second most diverse phylum of animals. The name “mollusca” signifies a soft body, since the earliest descriptions of mollusks came from observations of unshelled cuttlefish. Mollusks are predominantly a marine group of animals; however, they are known to inhabit freshwater as well as terrestrial habitats.
CHARACTERISTICS OF MOLLUSCA:
- 1. They have soft un-segmented bodies.
- 2. They possess muscular foot adapted for crawling, or burrowing.
- 3. The body is covered by a soft tissue called Mantle.
- 4. Some have calcerous shells e.g. Snails while others have no shells e.g. Octopus and Slug
- 5. Some are aquatic while others are terrestrial.
Example are: Squid, Mussel, Periwinkles, Snails, Oysters and Slug.
Arthropods are invertebrate animals having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes chelicerates, myriapods, and crustaceans. It is divided into the following classes:
CHARACTERISTICS OF ARTHROPODA:
- 1. They have segmented bodies.
- 2. They have hard, rigid exoskeleton made of chitin.
- 3. They have jointed appendages or jointed legs used for Feeding, Movement, and Reproduction or as Sensory Organs.
- 4. They are aquatic while others are terrestrial.
- 5. Their bodies are divided into two or three segments such as the Head,Thorax and Abdomen which may be fused in some members.
- 6. Their bodies are bilaterally symmetrical.
- 7. They are triploblastic i.e. they have three body layers.
- 8. They have various means of respiration e.g Gill, Trachea, Lung, Book or body surface.
Examples of Arthropoda are:
- Insecta: e.g Grasshopper, Cockroach, Housefly, Butterfly etc.
- Arachinda: e.g Spider, Scorpion, Mites, Ticks etc.
- Crustaceans: e.g Crab, Crayfish, Shrimps, Prawns, Lobsters etc.
- Myriapoda: e.g Centipedes and Millipedes.
STRUCTURAL DIFFERENCES BETWEEN CRUSTACEANS, INSECTS AND ARACHNIDS
|1.||Body Division||Two i.e. Cephalothorax and Abdomen||Three i.e. Head, Thorax and Abdomen||Two i.e. Prosoma and Opisthosoma|
|3.||Eye||A pair of Stalked Eyes||A pair of Compound Eyes||Eight simple Eyes|
|4.||Antenna||2 pairs||A pair||None|
|5.||Walking legs||5 pairs of Jointed-legs||3 pairs of Jointed-legs||4 pairs of Jointed-legs|
|6.||Respiratory Organ||Gills||Trachea||Lung Books|