Introduction to Arthropoda

The arthropods are by far the most successful phylum of animals, both in diversity of distribution and in numbers of species and individuals. They have adapted successfully to life in water, on land and in the air.

About 80% of all known animal species belong to the Arthropoda - about 800,000 species have been described, and recent estimates put the total number of species in the phylum at about 6 million.

Arthropods are found in a greater variety of habitats than any other animal group; on top of mountains, at great depths in the ocean and in the icy wilderness of Antarctica. They can survive great extremes of temperature, toxicity, acidity and salinity.

Evolution Probably evolved from a Peripatus( 栉蚕 ) - like ancestor, which in turn evolved from a segmented worm Probably evolved from a Peripatus( 栉蚕 ) - like ancestor, which in turn evolved from a segmented worm

Characteristics of Arthropoda

Metamerism( 体节性 ) Metamerism- body is segmented. Exoskeleton and metamerism causes molting

Exoskeleton( 外骨骼 ) Exoskeleton- body covered with a hard external skeleton Why an exoskeleton? Why not bones? Exoskeleton good for small things, protects body from damage (rainfall, falling, etc.). Bones better for large things

Bilateral Symmetry Bilateral Symmetry- body can be divided into two identical halves

Jointed Appendages Jointed Appendages- each segment may have one pair of appendages, such as: legs wings mouthparts

Open Circulatory System Open Circulatory System- blood washes over organs and is not entirely closed by blood vessels. Our system is a closed one

Ventral Nerve Cord Ventral Nerve Cord- one nerve cord, similar to our spinal column

Classes of Medical Importance

SUBPHYLUM Crustacea (Formerly a Class) 甲壳纲 Lobsters, crayfish, shrimp, and others Primarily aquatic Free-floating larval stage 26,000+ known species Branched appendages: gills on legs, for example, in a lobster

Class Diplopoda Millipedes milli means thousand, pede means legs, so ('thousand legged creature'?) Most feed on decaying matter Diplo means two, poda means feet, so two pair of legs per segment Generally harmless detritus feeders pests in nursing homes. Some species can eject cyanide (poison), so be careful if traveling to South America

Class Chilopoda Centipede 蜈蚣 Centi means hundred, pede means legs, so "hundred legged creature"? 1 pair of legs per segment Usually shiny, reddish brown, less than 3 inches long Move rapidly, often found under logs; some in homes Can bite have poison claws- modified 1st pair of legs supposedly feels like a bee sting

Class Arachnida Ticks, mites, and spiders No antennae Two body regions: cephalothorax and abdomen Feeding appendages are chelicerae Most are carnivorous They hold the prey with chelicerae, and pour enzyme-rich salivary juices over the victim Digestion is mostly external Most are terrestrial 57,000 known species

Class Insecta The insects are the most numerous and diverse of all the groups of arthropods. There are more species of insects than species in all the other classes of animals combined!!

Class Insecta Insects differ from other arthropods in having three pairs of legs. In size, insects range from less than 1 mm to 20 cm in length, the majority being less than 2.5 cm long.

characteristics 3 body segments- head, thorax (chest), abdomen (stomach area). Insect means in (into) sect (cut).

Class Insecta 1 pair of antennae

Class Insecta Tracheal Respiratory System- composed of tubes, with holes (spiracles) through the body that admit air. So, they do not have lungs at all.

Class Insecta Wings- usually two pairs of wings, although some have one pair of wings, or none. No other class of arthropods has wings. (Have you ever seen a flying Lobster?!)

Class Insecta 3 pair of legs, 1pair to each of the 3 thoracic segments. Compound eyes, with facets (ommatidia 小眼 ).

Insect mouthparts 1. chewing (beetles, cockroaches). 2. piercing-sucking (mosquitoes, bugs). 3. lapping and sponging (flies).

Insect Growth Basics Insects develop from egg. Eggs come in a variety of shapes and sizes. They hatch from the egg, and begin eating Sooner or later they become too big for their exoskeletons. They Molt, or shed their skins. Molting is the shedding of old cuticle and expanding into a new and larger one. metamorphosisChanges in the insect may occur with each molt. This is called metamorphosis, or a change in form.

Types of Metamorphosis Partial metamorphosis (gradual, incomplete) Complete metamorphosis *most advanced*

Incomplete Metamorphosis Gradual change in appearance. For example,wing pads grow longer with each molt, and eventually into wings in the adult. Immature forms are called NYMPHS Generally have the same food source as the adult.

Complete Metamorphosis Immature is called a larva, with larva perhaps having separate food source from the adult. Larva and adult may have radically different food sources,with very different environments. Example: Butterflies. Or, they may have same food source: bees.

Harmful effects of arthropods 1. Direct harm a. Annoyance-flies interfere with your work and rest. b. Venom-stings of scorpions and spiders may even cause death. c. Parasites-Fly larvae may cause myiasis, scabies and mange are caused by Sarcoptes scabiei.

Harmful effects of arthropods 2. Transmission of diseases: a. Mechanical transmission. b. Biological transmission. Pathogens spend a part of their life cycle in the arthropods. a) Propagative b) Cyclopropagative c) Cyclodevelopmental c. Transovarian.

b) Cyclopropagative-The pathogenic organisms undergo a developmental cycle in the arthropod with multiplication and change in form. Plasmodium sp. In anopheline mosquitoes. c) Cyclodevelopmental- The pathogenic organisms undergo a change in form without multiplication. Filaria in mosquitoes.