What is an Arthropods?

ARTHROPODS



Arthropods are known as one of the largest phylum of animals, there are 4 sub phyla (Crustacea, Chelicerata, Trilobita and Uniramia) with in this group, which have adapted to all environments. Arthropods are very diverse and abundant because of there long existence and are characterized by there hard exoskeleton and segmented body with joint appendages.


For more pictures of Arthropods please click on the image below to go to a new site:



Vocabulary: Click words in bold and underline for definition.
[UNDER CONSTRUCTION]
Word

link for Vocab http://arth12.blogspot.com/2007/04/digestion.html

General Characteristics and Anatomy

leg of a spider
The success of the arthropods has resulted from its body structure. There hard exoskeleton (made of chitin) is used for protection and prevent them from drying out. Though the down fall of the exoskeleton is that it won’t grow as the animal grows, therefore the arthropods will either molt or shed their exoskeleton. They have two to three main segments, a head, a thorax and an abdomen. Some have evolved into only having an abdomen and a cephalothorax. As body segments are lost so are appendages. All of the appendages in an arthropod have evolved into structures that benefit them in their environment; they include claws, antennae, wings, flippers, and etc. The appendages are used for feeding, defence, locomotion, and sensory reception.


trilobite fossil
Trilobita
-Have been extinct from earth about 250 million years ago
-The body of the first arthropods were believed to have similar structures.
-Have a thick tough exoskeleton with many segments, each segment was connected to a pair of appendages which was further divided to form to branches.


lobster
Crustacea (ex. Lobster, Barnacles, Krill)
-Are characterized by: a hard exoskeleton, two pairs of antennae, and mandibles(mouthparts).
-Three body parts (head, thorax, and abdomen)
-Appendages development

-1st pair -used for sensing surroundings (antennae)
- contain sensory hairs
-movement (water fleas, push through water)
-feeding (filter feeding)

-3rd pair -mandibles (mouth parts)
-many use them as short heavy structures used for
biting/ grinding
-some use them for feeding (filter feeding,
locating food or sucking blood from a host)


lady bug
Uniramia (ex. butterfly, millipede, flea)
-largest subpyla
-has 1 pair of antennae and appendages
-inhabit almost all terrestrial habitats on earth
-some live in aquatic conditions

Centipedes
-carnivores
-pair of poisonous claws located on the head
-15-170 pairs of legs
-1 pair of appendages per segment except 1st segment and last 3 segments

Millipedes
-2 pairs of appndages per segment
-live in damp places
-feed on dead and decaying plant material
-roll into a ball for defence
-some also defend thereself by producing unpleasent/toxic chemicals

Insects
-3 main segments (head, abdomen, and thorax)
-3 pairs of legs attached to thorax
-1 pair of antennae (on head)
-1 pair of compound eyes (on head)
-2 pairs of wings (on thorax)
-breath with tracheal tubes


spider
Chelicerata (ex. spider, scorpion, mite)
-don't have antennae (sensory "feelers"
-2 part body
-cephalothroax (anterior end, includes brain, eyes, mouth, mouthparts and esophagus, posterior end includes front part of digestive system and legs)
-abdomen (internal organs)
-2 pairs of appendages attached near mouth
-1st pair chelicerae
-2nd pair pedipalps

Habitat and Adaptations

grasshopper

Habitat
Arthropods have adapted to all habitats from aquatic to terrestrial.
Example of habitats would be the ocean, forest, desert, inside of the earth, etc.

Adaptations
In order for arthropods to survive where it lives it has to adapt to the conditions. Depending on location, what it eats, and living standards, etc.

Aquatic Arthropods have gills to breath with in water and sensory organs to detect prey and predetors all around their bodies, and mandibles. Some have claws to rip apart there prey like a lobster while others may be filter feeders.

Arthropods that live in colonies have to have special ways to communicate to each other, take the bee for instance it has diffrent dances by movin it self in certain directions ex. the round dance is used to tell other bees it has found food within 50m of the hive.

Some arthropods camouflage themselves for protection of surprise attacks on the prey for example if a stick grasshopper was on a pile of leaves many would think it was a branch instead of an animal.

These are only some examples, there are a wide range related to all parts of their body, size, amount of legs, etc.

Respriation

Arthropods don’t have lungs but they have other ways of getting oxygen through their bodies, by using spiracles, gills, book lungs or even a combination of more then one.

Aquatic arthropods use gills for breathing; as water flows into their bodies the gills draw oxygen out of the water. They also use a movement of the mouth parts and other appendages to keep water flowing into their gills.

Insects, centipedes and millipedes breath through tiny holes along the sides of their thoraxes or abdomens called spiracles. The spiracles then lead to tracheas which transport air though their bodies.

While some chelicerata take air through book lungs, which are a series of folds with in their exoskeleton. Air passes between folds and mixes with the blood and then circulates around the body. Arachnids with book lungs also have tracheas to transport air into their bodies.

Circulation/Internal Transport

Arthropods have a well developed heart that pumps blood through an open circulatory system. In the terrestrial arthropods they have a heart that is stretched along the abdomen, while in the aquatic arthropods their hearts are smaller and located in the center of their bodies. As the heart contracts, blood travels through the body and then leads back to a cavity around the heart and re-enters through openings.

A cool site for aquatic circulatory system (lobster) please click image below:

Feeding, Digestion and Excretion

Feeding
In the phyum Arthropoda has every mode of feeding is seen from carnivores (ex. spider, scorpion), herbivores (ex.ants, butterflies), parasites(ex. ticks, lice), filter feeders (ex. barnacles) and detritus feeders. Each type of preditors have had their appendages evolved in diffrent ways to suit their enviorment like mouth parts.

Digestion
Due to the fact that there are millions of arthropods that live in diffrent habbitats and feed on diffrent things the digestive tract varies for each animal. An example of a digestive tract would be the grasshopper, where food enters the mouth and then is leaded to esophagus, pharynx, crop (where food is stored), intestine, rectum and food is then excreted through the anus.

Excretion
-Solid undigested food is excreted through the anus

Terrestrial arthropods
-deposite nitrogen-containing waste(from cellular metabolism)
-removed by using a set of Malpighian tubules (located in the body sinuses)
-remove waste from blood, concentrates it, and is then mixed with the undigested therfore it is now solid and removed through the anus
-some have small excretory glands at bases of legs instead/in additon of malpighian tubules

Aquatic arthropods
-deposite nitrogen-containing wastes
-by a pair of green glands found by base of antennae it is then emptied through a pair of opening on the head

Response To Environment/Movement

wasp
pill bug
grasshopper

Response
Most arthropods have well-developed nervous systems. They use a pair of ganglia located in the head and two long nerves near the esophagus that connect to the brain. From the brain a nerve cord with several more gangila, is connected and runs along the ventral part of the body. The ganglia serve as the main controls which coordinate the movements. Each major part of the arthropod are controled by several ganglia.

Arthropods also use sense organs such as statocysts ,chemical receptors. Arthropods also have many other sophisticated sense organs like compound eyes that can detect things our eyes cant.

Crustaceans and insects also sense things using their taste receptors and sensory hairs. Taste receptors are located in the mouth and in other strange places like their antenae and legs. Many insects have eardrums to detect movement of preditors or prey.

Movement
Arthropods use a muscle system that is controled by their nervous system for movement. When the muscles contract it generates a force which is then transfered to the exoskeleton. At each body joint there are muscles that are functionized to either extend or contract. When the arthropods use these muscles to pull against their exoskeleton it allows them to beat their wings against the air or push of the ground and other movements.
Most arthropods are motile only a few like the barnacles are sensile.

Reproduction, Growth and Development

Reproduction


Spiders
dragon flies mating
scorpion with babies

Reproduction in an arthropod requires a male and a female of the same species to mate in order to form offspring. The males produce sperm while the females make eggs, they are then fertillized. Some arthropods lay their eggs while others carry them. An example of an arthropod that carries the eggs would be a scorpion, when the babies hatch they crawl out on to her back until they are ready to go on their own.
Arthropods eggs must stay moist so most lay them on or near the water; however, some keep their eggs moist in other ways. For example spiders create an egg sac that wraps around the eggs like a cocoon, which also protects them from predators.
There are also few arthropods that guard their eggs in special openings of their exoskeleton for example the crab or shrimp.
Arthropods that live in colonies will work together to watch over the eggs of all members, for example bees and ants.


Spider molting
Growth
In order for an arthropod to grow they must molt or shed their exoskeletons, during this process the arthropod is completely defenceless from predetors, therefore they hide. The process of molting can take from a few hours to a few days.

Development
Incomplete Metamorphosis v.s. Complete Metamorphosis

(click image to enlarge in a new window)
grasshopper undergoes incomplete metamorphosis VS butterfly undogoes complete metamorphosis

Incomplete Metamorphosis
-hatch from eggs
-look like adult form
-when young, they lack adult structures such as sex organs and wings
-keep molting until they reach adult stage during that period they acquire adult characteristics
(egg > nymph > adult)

Complete Metamorphosis
-eggs hatch to larvae(look nothing like the adult)
-larvae molts to get bigger but hardly changing in appearance
-then larvae sheds larval skin becoming a pupa
-pupa stage -insect body breaks down larval structures in order to supply raw
materials for adult structures
-when complete the "adult" emerges
-adult is compeltely different from befor(internal and external)
(egg > larvae > pupa > adult)
-Metamorphosis controlled by complicated interaction of hormones(including molting hormone)
-juvenile hormone helps keep it in the right stages depending of maturity
-the hormones are critical to the arthropods development

Vocabulary

Arachnid- chelicerata arthropod with four pairs of legs on its cephalothorax and no antennae

Arthropod- animal having a segmented body, an exoskeleton containing chitin, and a series of jointed appendages belonging to the phylum arthropoda

Appendages- extended body parts such as arms or legs

Chelicerate- arthropod characterized by a two-part body and mouthparts called chelicerate

Cephalothorax- fused head and upper body of some arthropods
Spiracles- a small paired aperture along the side of the thorax or abdomen of an insect or spider through which air enters and leaves

Chitin- complex carbohydrate found in arthropod exoskeletons and fungal cell walls

Crustacean- arthropod characterized by a stony exoskeleton, two pairs of antennae and mandibles

Exoskeleton- system of supporting structures covering the outside of the body

Ganglia- small cluster of nerve cells

Gills- the organ that fish and some other aquatic animals use to breathe, consisting of a membrane containing many blood vessels through which oxygen passes.

Mandible- mouthpart designed for biting and grinding food

Metamorphosis- series of dramatic changes in body form in the life cycle of some animals

Molt- to shed an exterior layer of skin, feathers, or an exoskeleton

Pheromone- specific chemical messenger produced by an organism that effects the behaviour and development of other individuals in the species

Pupa-resting stage of metamorphosis in which tissues are of an insect are organized into the adult form

Sinuses- a widened channel containing blood, especially venous blood

Tracheae-a tube in insects and related air-breathing animals through which air is drawn into the body by the pumping action of the abdominal muscles

Tracheal system- the system to do with the tracheae

Trilobite- sea-dwelling organism belonging to the oldest, now extinct, subphylum of arthropods

Uniramian- member of the largest subphylum of arthropods contains centipedes millipedes and insects

Connection To Other Phyla

velvet worm
Arthropods are the oldest phyla of animals and belived to have existed over 600 million years ago. Since that time they have changed dramatically to fit their enviorment.
Arthropods such as insects, centipedes and millipedes are believed to have evolved from ancestors that were closely related to the modern annelids. An example of this is the velvet worm where it has both characteristics of an annelid and an arthropod.
Where as other arthropods such as the crustaceans, spiders, and trilobites evolved from older and distantly related ancestors.

Lab Photos

Interesting Facts

Japanese spider crab

The largest living arthropod is the Japanese spider crab. They can be found in the Pacific Ocean near Japan. Their legs can be as long as 13 feet and their body size can reach up to 15 inches.


Dragonfly


The fastest flying insect in the world is dragonfly. Their speed range from 30 to 60 km/hour!


horseshoe crab

(subphyla:Chelicerates)
Horseshoe crab's blood is blue! This is due to a high content in copper-based hemocyanin instead of the iron-based hemoglobin found, for example, in humans.

Bibliography

"Arthropod". Wikipedia. April 2007.
<http://en.wikipedia.org/wiki/Arthropod>.

Cole, Joanna. An insect's body. New York: William Morrow and Company, 1984.

"Dragonfly". Wikipedia. Febuary 2007.
<http://en.wikipedia.org/wiki/Dragonfly>.

Ganeri Anita. Insects. United States: Franklin Watts, Inc., 1992.

"Horseshoe Crab". Wikipedia. March 2007.
<http://en.wikipedia.org/wiki/Horseshoe_crab>.

"Japanese Spider Crab". Wikipedia. March 2007.
<http://en.wikipedia.org/wiki/Japanese_spider_crab>.

Miller, Kenneth R. and Levine, Joseph. Biology. United States: Prentice Hall,1998.

Smithyman, Kathryn. and Kalam, Bobbie. What is an Arthropod?. Ontario:
Crabtree Publishing Company, 2003.

** For correct bibliography format heat to "dashboard>> Aurthropod>> new post >> edit post >> Bibliography >> edit >> compse"