Arthropoda Lecture

8/8/2019 Arthropoda Lecture

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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 recentestimates 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 theocean and in the icy wilderness of

Antarctica. They can survive great

extremes of temperature, toxicity, acidity

and salinity.



Characteristics of Arthropoda



Metamerism

Metamerism- body is segmented.

Exoskeleton and metamerism causes

molting



Exoskeleton

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)

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 meanslegs, 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 becareful if traveling to South America



Class Chilopoda

Centipede Centi means hundred, pede means legs, so

"hundred legged creature"?

1 pair of legs per segment

Usually shiny, reddish brown, less than 3inches long

Move rapidly, often found under logs; some inhomes

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 thanspecies 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 inlength, 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 flyingLobster?!)



Class Insecta

3 pairs of legs, 1pair to each of the 3

thoracic segments.

Compound eyes, with facets (ommatidi).



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 avariety of shapes and sizes.

They hatch from the egg, and begin eating

Sooner or later they become too big for theirexoskeletons.

They Molt , or shed their skins. Molting is theshedding of old cuticle and expanding into a

new and larger one.

Changes in the insect may occur with eachmolt. This is called metamorphosismetamorphosis , or achange 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 witheach molt, and eventually into wings inthe adult.

Immature forms are called NYMPHS

Generally have the same food source asthe adult.





Complete Metamorphosis

Immature is called a larva , with larvaperhaps having separate food sourcefrom the adult.

Larva and adult may have radicallydifferent food sources,with verydifferent environments.

Example: Butterflies.Or, they may havesame 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 spenda 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 withoutmultiplication. Filaria in mosquitoes.

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Arthropoda Lecture