Phylum Arthropoda

Arthropoda Classification Phylum Arthropoda Subphylum Uniramia- (terrrestrial mandibulates) Class Chilopoda- centipedes Class Diplopoda- millipedes Class Insecta- insects Subphylum Crustacea- (aquatic mandibulates) lobsters, crabs, crayfish, shrimp, sow bugs (pill bugs), krill and barnacles Subphylum Chelicerata Class Arachnida- spiders, scorpions, ticks, and mites Class Merostomata- horshoe crab Class Pycnogonida- sea spiders Subphylum Trilobita- trilobites (extinct)

ARTHROPODS

The phylum Arthropoda includes lobsters, spiders, scorpions, millipedes, & insects; it encompasses over one million species. They are the most abundant of all the visible animals. Arthropods live virtually everywhere, and their influence on man & the environment is great.

Negative Influences 1. Can destroy crops 2. Compete with other animals for food 3. Transmit deadly diseases 4. Annoying pests Positive Influences 1.Produce valuable things such as wax, honey, drugs, & silk. 2.Help maintain plants & crops by assisting cross-fertilization 3.Help control the number of harmful arthropods 4. New & better machines have been designed after them 5. Food source for other organisms 6. Recycle nutrients by decomposing things Arthropoda Influence

Characteristics of Arthropods 1. Exoskeleton--non-living body covering secreted by the epidermis. Three layers of the exoskeleton: A. Outer layer--coating of proteins and lipids that repel water and prevent water loss (in land species) B. Middle layer--supporting layer; primarily protein & chitin Chitin--chemical component (polysaccharide) that gives the body covering toughness & flexibility. C. Inner layer--similar to middle layer but provides more flexibility at the joints. Mineral salts in the exoskeleton protect the animal from harsh chemicals in its environment and from the attacks of predators.

Important Polysaccharides Four Important Polysaccharides: Starch ~ used for energy storage for plants; major source of energy for animals. Glycogen ~ starches from plants are broken down and made into glycogen for temporary storage in animals Cellulose ~ chains of glucose molecules found in plant cell walls; structural; large molecules that most animals can’t digest. Chitin ~ strong, insoluble yet very flexible, similar to cellulose. One of the most abundant polysaccharides in nature, makes up the exoskeletons of arthropods (insects, crustaceans, spiders); structural

Figure 3.7 Starch granules in potato tuber cells Glycogen granules in muscle tissue Glycogen Glucose monomer Starch Cellulose Hydrogen bonds Cellulose molecules Cellulose microfibrils in a plant cell wall

Exoskeleton Pros 1. Provides more protection from predators and the environment Cons 1.The weight of the armored body covering limits the size of the animal 2.Poses an obstacle to growth Molting--to shed its covering in order to grow. To molt, the arthropod epidermis produces enzymes that eat away at the inside of the old exoskeleton while a new exoskeleton is produced beneath it. Once free from its former exoskeleton, an arthropod may go into seclusion until its new, expanded exoskeleton hardens.

2. Jointed Appendages--"arthropoda" means "joint-footed" and describes the appendages of this group. The muscles of the arthropod move the limbs from within the exoskeleton. Variety of form & function in arthropod appendages: A.Limbs, legs--ex. spider, grasshopper--for locomotion B.Fangs--ex. centipede--enable it to capture & chew its food. C.Claws--ex. lobster, crabs--means of defense. D.Antennae--ex. insects--sensory reception. E.Stinging tail--ex. scorpion--defense and predation. Characteristics of Arthropods

3. Body Segmentation--body of the typical arthropod is divided into 3 segments: A.head B.thorax C.abdomen the head and the thorax are often united into what is referred to as the cephalothorax these body segments are designed for specific functions. Characteristics of Arthropods

4. Open circulatory system w/ a dorsal heart--the dorsal heart pumps blood through short vessels that empty into cavities within its body and bathe its organs. Characteristics of Arthropods

5. A ventral nervous system--arthropod nervous system consists of a "brain" (a pair of ganglia) centered over the esophagus and joined by 2 major nerves to a ganglion below the esophagus, and a ventral nerve cord. Characteristics of Arthropods

VENTRAL NERVE CORD *Ventral location provides protection and places it in close proximity to the appendages which are the structures most often requiring nervous commands and coordination.

Nervous system organs: Antennae--appendages in the head region; provide taste, smell & touch sensation to most arthropods. Compound eyes--(in most insects & crustaceans) contain thousands of individual lenses set at slightly different angles providing a mosaic view. Simple eyes--(like in spiders) contain only one lens and have very limited view.

ANTENNAE COMPOUND EYES SIMPLE EYES