1. AEB121: INVERTEBRATE ZOOLOGY PHYLUM ARTHROPODABY
MRS OZEMOKA H.J.
AEB121: INVERTEBRATE ZOOLOGY PHYLUM ARTHROPODA by MRS OZEMOKA H.J. is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

2. PRE- TEST What are Arthropods? Give exmples of Arthropods you know.
State the classes of Arthropods.
Give some characteristics of Arthropods.
Why are they very successful on land.
Name the classes of Arthropods.
Give the economic importance of Arthropods.

3. INTENDED LEARNING OUTCOME
At the end of the class, the students should be able to know the following:
The meaning of Arthropods.
The characteristics of Arthropods.
The reasons for abundance and diversity of Arthropods.
The various classes of Arthropods.
The economic importance of Arthropods.

4. INTRODUCTION
Arthropoda is from a Greek word( Arthron, joint + pous podos foot). It is currently the most species diverse Phylum in the animal kingdom.It contains about 80% of animal kingdom. It includes spiders, scorpions, ticks, mites, crustaceans, millipedes, centipedes, insects and other less well known groups.

5. EXAMPLES OF ARTHROPODS

6. REASONS FOR DIVERSITY AND ABUNDANCE OF ARTHROPODS
The diversity and abundance of Arthropods are due to structural and physiological patterns which are as follows.
A VERSITLE EXOSKELETON: They possess an exoskeleton which is highly protective. The skeleton is the cuticle which often contains protein and lipids. The protein is stabilized and hardened by cross linking chemicals(sclerotization). This process of sclerotization increases the protective ability.
SEGMENTATION: The presence of segments as well as appendages, creates room for efficient locomotion. The segmentation however undergoes tagmation (fusing of segments) e.g spiders have two tagmas while insects have three tagmas

7. CONTINUATION OF REASONS FOR ABUNDANCE.
EFFICIENT RESPIRATORY MECHANISM: Terrestrial Arthropods have a highly efficient tracheal system whereby air is piped directly to the cells. The air tubes delivers oxygen directly to the tissues and cells and make a high metabolic rate possible during periods of intense activity. This system also tend to limit body size. Aquatic Arthropods respire mainly by means of external and internal gills.
HIGHLY DEVELOPED SENSORY ORGANS: They possess sensory organs which occurs in various forms from compound (mosaic) eyes to organ of touch,smell, hearing, balancing and chemical reception. Arthropods are keenly alert to what happens in their environment.

8. CONTINUATION OF REASONS FOR ABUNDANCE.
COMPLEX BEHAVIOURIAL PATTERNS: Arthropods exceed most other invertebrates in complexity and organization of their activities. Innate (unlearned) behavior unquestionably controls much of what they do but learning also play an important part in the lives of many species e.g. social behavoiur.
USE OF DIVERSE RESOURCES THROUGH METAMORPHOSIS: Many Arthropods pass through metamorphic changes including a larval form quite different from the adult in structure. The larval forms are adapted from eating food different from that of the adults.

9. CHARACTERISTICS OF ARTHROPODS
They possess jointed appendages. One pair on each segments and often modified for specialized functions.
They are cosmopolitan and many are capable of flight.
Some are free living while others are parasitic.
They possess triploblastic body.
They are bilaterally symmetrical with segmented body which is divided into functional groups called tagmata either cephalothorax(head and thorax) or head, thorax and abdomen.

10. CHARACTERISTICS OF ARTHROPODS CONTINUES
The adults have a reduced body cavity which is filled with blood (haemocoel).
They possess culticular exoskeleton.
They have a complete digestive system.
They possess a complete muscular system with exoskeleton for attachment, striated muscles for rapid actions and smooth muscles for visceral organs but no cilia.

11. ILLUSTRATION OF THE MUSCULAR SYSTEM
ATTACHMENT
MUSCULAR SYSTEM
RAPID ACTION
EXOSKELETON
STRAITED MUSCLES
SMOOTH MUSCLES
VISCERAL ORGANS

12. CHARACTERISTICS OF ARTHROPODS CONTINUES
Nervous system consist of dorsal brain connected by a ring around the gullet to a double nerve chain of ventral ganglia. In some species, there is fusion of ganglia.
They have well developed sensory organs, behavioural patterns much more comple than those of most invertebrates with wider occurrence of social organization.
Sexes are separated , fertilization is internal and associated with metamorphosis.
Parthenogenesis also occur in some taxa.

13. CHARACTERISTICS OF ARTHROPODS CONTINUES
Excretory organ is the malpighian tubules. They also have the paired excretory glands called the coxal, anntenal or maxillary glands.
Respiration is by body surface, gills, trachea(air tubes) or book lungs.
They have an open circulatory system with dorsal contractile heart and arteries and haemocoel (blood sinues).

14. CLASSIFICATION OF PHYLUM ARTHROPODA
Arthropods are typically classified into five subphyla, of which one is extinct.

15. CLASSIFICATION SUBPHYLA PHYLUM ARTHROPODA TRILOBITA CHELICERATA
MYRIAPODA
CRUSTACEANS
HEXAPODA

16. SUBPHYLUM TRILOBITA
It literally mean three lobes. They are however extinct, they were all marine and existed from Cambrian to carboniferous period. There bodies were divided into three longitudinal lobes. They possessed head, thorax and abdomen, one pair of antennae and biramous appendages. They crawled along substrates feeding on annelids, molluscs and decaying organic matter. They had the ability to roll into a ball to protect their ventral surface. The inner lobe was a walking leg while the outer lobe bore spikes or teeth which was either used in digging, swimming or as gills for gaseous exchange.

17. SUBPHYLUM CHELICERATA
It includes organisms like mites, ticks, spiders, horse shoe crabs and sea spiders, scorpions etc. They possess two body segments: prosoma or cephalothorax and opisthosoma (abdomen). The prosoma is a sensory, feeding and locomotor tagma. The prosoma bears the simple eyes but lacks antennae. Paired appendages attaches to the prosoma. The first pair is called chelicerae(pincerlike or chelate) used for feeding. The chelicerae may also be specialized as hollow fangs or used for various functions. The second pair is called pedipalps which are sensory in function but may also be used for feeding and locomotion. The opisthosoma contains the reproductive, digestive and excretory organs.

18. CHELICERATA
MEROSTOMATA
ARACHNIDA
PYCOGONIDA
The subphylum Chelicerata conist of three classes namely: Merostomata, Arachnida and Pycogonida

19. CLASS:MEROSTOMATA.
It includes the horse crab and water scorpions. They use book gills for gaseous exchange. They have open circulatory system. They are diecious. During reproductive period, the male mount the female grasping her with its pedipalps (first pair of walking legs).The female shed eggs in depressions in the sand, the male fertilizes the laid eggs. The fertilized eggs are covered with sand and develop unattended.

21. CLASS ARACHNIDA Examples includes spider, ticks, mites, scorpions etc.
Characteristics.
SPIDER

22. CLASS PYCOGONIDA
Example includes sea spider
Characteristics.

23. SUB PHYLUM MYRIAPODA
Many legged Arthropods called millipede and Centipede.