Intro to Arthropods

Members of this phylum vary greatly in…

size, shape, and habits

List the 4 subphyla of Arthropods and their scientific names.

Trilobites (Trilobita)

Chelicerates (Chelicerata)

Crustaceans (Crustacea)

Insects + close relatives (Uniramia)

What is the oldest subphylum?

Trilobita

Which arthropods are included in Trilobita?

Ancient trilobites, dwellers of ancient seas

Which arthropods are included in Chelicerata?

Spiders, mites, ticks, scorpions, and horseshoe crabs

Which arthropods are included in Crustaceans?

Crabs and shrimp

Which arthropods are included in Uniramia?

Centipedes, millipedes, and all other insects

Why are there so many arthropods?

• Evolving on earth for a long time

• This means they have experienced several adaptive radiations
  (Due to wide range of adaptations and ability to exploit various ecological niches. )

Why are the ancestors of arthropods unknown/debated on?

They were soft bodied, meaning that they left little/few fossils behind (little evidence)

Which arthropods evolved from wormlike animals?

Insects, centipedes, and millipedes

Which arthropods evolved from more ancient/distantly related ancestors?

Crustaceans, spiders, and extinct trilobites

What was a typical trilobite’s body composed of?

• Thick outer covering

• Many segments

• Each segment has a pair of appendages

What was each appendage on an ancient trilobite divided to form?

It formed two branches: A walking leg and a featherlike gill

What are the two evolutionary trends exihibited away from the trilobite form?

• Tagmatization: body segments fuse together to form larger functional units called tagmata

• Appendages becoming modified to support feeding, locomotion, and other functions

What are the three most important arthropod features?

1. Segmented body

2. Hard exoskeleton

3. Series of jointed appendages

What are other characteristics that arthropods hold?

1. Brain in the dorsal part of the head (at the top)

2. A ventral nerve cord

3. Open circulatory system powered by a single heart

Exoskeleton

A system of external supporting structures made out of the polysacchrite chitin and protein.

What is the range of texture of an exoskeleton?

Extreemly hard or extremely flexible

What are three advantages that an exoskeleton provides?

1. Protection from physical damage

2. A waterproof coating to restrict water loss and allow for adaptibility to dry environments

3. Ability to move efficiently

What are some disadvantages of an exoskeleton?

1. Is not living tissue; meaning, it cannot grow as the arthropod grows.

2. Movement can only occur at the joints of the exoskeleton.

What are inside crustacean exoskeletons that make them rigid? Why might they need to be this way?

Calcium salts - it is more advantageous in teir environment.

What enables arthropods to move?

Jointed appendages

What do arthropod appendages include?

antennae, claws, walking legs, wings, flippers, and other specialized structures

Describe the variation of segmented bodies in arthropods.

• Millipedes and centipedes have many visible segments

• Insects, spiders, ad crabs, have lost segments due to evolution OR had segments fuse together to form larger body parts.

Name 3 examples of the diversity of feeding modalities in arthropods.

1. Drinkin/nibbling bodily fluids (parastic arthropods)

2. Some herbivorous arthropods are very specific abou what part of the plant they eat

3. Some carnivorous arthropods catch and eat other animals

How do many marine arthropods eat?

By filter feeding using comblike bristles located on mouthparts of legs to tiny plants and animals from the water

What are the three basic respiratory structures found in arthropods?

1. Gills

2. Book lungs/book gills

3. Tracheal tubes

Is it possible for some species to have both trachel tubes and book lungs?

Yes, it is rare though

Do all arthropod species have respiratory structures?

No.

What do gills look like and where are they located?

They look like a row of feathers just under the cover of their exoskeleton.

Where are gills formed from

Part of the same appendages that form mouthparts and legs

How does water move into the gills?

Movement of the mouthparts and other appendages

What arthropod species have book gills? Where are they located?

Horsheshoe crabs. Beneath their body.

What arthropods have book lungs? Where is it located?

Spiders and their relatives. In a sac within the body.

In book lungs and gills, how are they structured and what does this allow for?

• There are layers of tissue which sit ontop one another, like pages in a book

• This allows for greater surface area, meaning more gas exchange

Which arthropods have tracheal tubes?

Terrestrial arthropods

How do tracheal tubes support respiration in these arthropods? 3 points. Also, what is repsriation powered by?

• Air enters into openings known as spiracles, which connect to the tracheal tubes

• The tracheal tubes reach deep into the animal’s tissues to supply oxygen via diffusion

• This motion is powered by the movements of body muscles

Do tracheal tubes work in larger arthropods?

No; they need a more efficient way to exchange gases

Explain the steps of internal transport in arthropods.

1. Blood is pumped through the arteries and into smaller blood vessels which enter the tissues

2. The blood leaves the blood vessels and flows into the sinuses

3. The blood collets in a large cavity surrounding the heart

4. Re-enters through small openings and the process begins again

How do do arthropods excrete solid wastes?

Undigested food goes out the anus

What structure do terrestrail arthropods use to excrete metabolic wastes?

A set of malpighan tubulues

How do malpighan tubules work to remove metabolic wastes in terrestrial arthropods?

1. These tubules are bathed in blood inside the body sinuses

2. They concentrate wastes from this blood and add it to the undigested food before it leaves the anus

What structures might terrestrial arthropods have in addition to or instead of Malpighan tubules?

Small excretory glans at the base of their les

How do aquatic arthropods remove metabolic wastes?

By diffusing them out through unarmoured places, such as the gills.

How else might aquatic arthropods excrete metabolic wastes?

A set of green glands located ear the base of the antennae are emptied out through a pair of openings in the head, such as in lobsters

Ganglia

A groups of nerve cells

Do most arthropods have ganglia?

Yes

What do the ganglia serve as?

central switchboards for incoming information and outgoing instructions to the muscles.

What runs down the ventral part of the body?

The ventral nerve cord

What are located along the ventral nerve cord? What do they do?

Several more ganglia located at each body segment to coordiante the movement of arms and legs (1 pair per segment)

What about ganglia in insects, where are they located?

Since segments have been fused together, there are several ganglia for each body part.

What is special about arhtropod vision?

• Compound eyes are used to gather information about the environment

• Many can see ultraviolet light

Where are the chemical receptors associated with taste and smell located?

mouths, antennae, and legs

How are crustaceans able to detect the movement of air/water?

Using sensory hairs

What is special about arthropod hearing? Where can they often be located?

• Goes beyond the human range

• Often located at odd places, such as the legs

List 4 modes of additional protection that arthropods use

• Venomous stings (scorpions, bees, ants) and venomous bites (spiders and centipedes)

• Attack using powerful claws (Lobsters and crabs)

• Camoflage

• Mimicry

How are muscle systems in arthropods coordinated?

Using the nervous system

What do muscles do in order to generate force, and where does that force go

Contract, the force is applied to the exoskeleton.

At each joint there are….

muscles for flexing and other muscles for extending.

How do arhtropods usually reproduce? Using what and how? Explain the process

Sexually, using internal ferrtilization and seperate sexes where the male will use a reproductive organ to inject sperm into the female or deposit sperm packets to which the female can collect

What must arthropods do in order to grow?

They must molt - shed their exoskeletons

What is the most important hormone that controls molting?

The molting hormone.

Summarize the 4 steps in molting.

1. Digesting and Chitin recycling

2. Secretion of a new exoskeleton and pulling out the old

3. Expansion of a new exoskeleton

4. Waiting period

Explain Digesting and Chitin recycling.

1. Near the motling period, the epidermis will digest the inner part of the exoskeleton

2. Chitin is absorbed to be recycled

Explain Secretion of a new exoskeleton and pulling out the old.

1. The animal’s cells will expand with water to push it out of the old exoskeleton

2. Often times, it will also eat its old exoskeleton

Explain Expansion of a new exoskeleton

1. Anthropod will become bigger

2. The new exoskeleton will stretch to cover it (still soft)

Explain waiting period.

1. The animal will wait for the exoskeleton to harden

2. This part takes from a few hours to a few days

3. Animal is often vulnerable during this time and will hide from predators

Metamorphosis

A dramatic change in form

Incomplete metamorphosis

Yougn that look like adults without functioning sexual organs and potentially wings, but aqquire these during the stages of molting and growth.

(Gradual growth)

First stage of complete metamorphosis and what it details?

Larval stage

• Eggs which hatch into larvae do not look like the parents

• As they grow, they molt repeatedly

• Once a certain age has been reached, the larvae will molt one last time before transforming into a pupa.
  

Second stage of complete metamorphosis and what it details?

Pupa stage

• The insects body will copletely re-arrange

• Adult structures grow from tiny buds

• Larval structures will supply raw materials for new adult structures

Third stage of complete metamorphosis and what it details?

Adult stage

• Internal and external body structures completely differ from the larval form when metamorphosis has completed.

What hormone reulates the stages of development for individuals who eihibit complete metamorphosis?

Juvenile hormone

What do high amounts of the juvenile hormone do?

They keep the insect in its larval form everytime it molts

What do low amounts of the juvenile hormone do? (when it drops past a certain threshold point)

They cause the insect to shift to the pupa stage

What does no amount of the juvenile hormone result in?

Pupa-adult molt

How can you combat insects? Why?

By tampering with their hormone levels as it is critical to their development

How do some plants defend themselves against insects?

By releasing chemicals which cause insects to develop at the wrong rate/keep them from being functioning adults.