Phylum Arthropoda(O and A-level biology)

Arthropods

General characteristics

1. have segments bodies
2. have exoskeleton
3. have jointed legs
4. they have a dorsal heart with an open vascular system

They are divided into five classes

1. crustacea
2. chilopoda
3. diplopoda
4. arachinida
5. insecta

Class crustacean

Characteristic

• have two compound eyes
• mostly aquatic
• have five or more pairs of legs.

Examples

Economic importance

Source of food to man and other animals

Few are parasitic

Class Chilopoda

Characteristics

Have cylindrical bodies with numerous segments each with one pair of leg.

Carnivorous

Example

Class Diplopoda

Characteristics

• their bodies are cylindrical with numerous segments that are similar except around the head region.
• Each segment has two pair of walking legs

Example

Adaptations of millipedes to the environment

• Exoskeleton prevents excess water loss.
• It has a dark color for camouflage from predators.
• Have eyes to see food and predators.
•  Have legs for locomotion to look for food and run away from predators.
• Has strong mandibles for chewing.

The detailed structure of the head of a millipede

Adaptations of the head of a millipede to survival of organism

• Eyes to see food
• Strong mandibles for feeding
• Antennae for feeling

Economic importance

1. Millipedes are herbivores and pest to farm crops.
2. They burrow and aerate the soil and improve drainage.

Class Arachnida

Characteristics

1. the body is divided into two main body parts, cephalothorax and abdomen
2. have no antennae
3. have four walking legs on cephalothorax

Examples

Economic importance

• Tick and mites are parasites to domestic animals
• Tick spreads diseases to man e.g. coastal fever
• Spiders feed on vectors.
• Scorpions and spiders inflict fetal stings

Adaptations of the tick to the mode of life

• Hard cuticle to prevent water loss and protects in parts
• Has dark color for camouflage
• Has strong teeth to cling on the host
• Has eyes to look for host.

Class Insecta

Characteristics

• has three main body parts; head, thorax, and abdomen.
• It has three pairs of legs.
• Thorax is divided into pro-, meso-, and metathorax.

Common insects include

Housefly

Order: Diptera

Characteristics of order Diptera

• one pair of wings
• hind wings are reduced to small knob-like structures or halters for  balancing.

Characteristics of housefly

• has a pair of compound eyes for vision
• has expanded or club-shaped proboscis
• has simple eyes (Ocelli)
• has a pair of wings and a pair of halters.
• The body is hairy.
• Has a pair of short hairy antenna

A drawing of housefly mouthparts

• maxillary pulps are flexible for handling and tasting food.
• Proboscis  is expanded to increase absorptive surface.
• Proboscis is tubular to suck liquid food

A drawing showing the tarsus of the hind limb of a housefly

Ecological significance of the structures of tarsus of a housefly

• claw are for griping on to the surface during walking
• hairs increase sensitivity
• jointed legs increase flexibility
• Arolium secretes a sticky substance that allows them to stick on the smooth surface during walking.

Life cycle of a housefly

Has a complete life cycle.i.e.

Economic importance

Transmits diseases e.g. dysentery, cholera, trachoma, typhoid fever and poliomyelitis.

Control

General cleanness and hygiene

Cover food

Eat hot food.

Use insecticides.

Cockroach

Order: Diptera

Characteristics of the order

• has biting mouthparts
• has threadlike antennae
• has a pair of anal cerci

Characteristics of a cockroach

 Has a long dorso-ventrally flattened body.

Has three main body parts: head, thorax, abdomen.

The head of cockroach

It is triangular

Adaptations of the cockroach head for its ecology

• has two pairs of compound eyes dorsolaterally located on the head for a large angle of vision.
• Ha modified mouthparts with strong mandibles for feeding
• Has a pair of long antennae for sensitivity
• the antennae are segmented to increase flexibility
• tapers from the head to reduce weight.
• Antennae are hairy to increase sensitivity
• Has broad base for firm attachment
• the thorax has two pairs of legs

Adaptations of hind limb to its function

• jointed for flexibility during movement.
• Long for quick movement.
• Has spine for defense: to pinch the enemy.
• Has areola to grip on smooth surface during movement.
• Has claws to grip cracked surface during movement.

Wings

The cockroach has two pairs of wings, outer and inner wing

Differences between outer and inner wings

Outer wing	Inner wing
1. Dark-colored 2. inflexible 3. not folded 4. Thick 5. narrow 6. opaque	1. Light in color 2. flexible 3. folded 4. membranous 5. broad 6.transparent

Adaptations of outer wings to their function

1. it is hard or stiff for protection
   1. dull / dark colored for camouflage
   1. slippery for protection against the grip of predator
   1. has veins for strengthening the wing

Adaptations of the inner wings to their functions

1. broad to generate repulsive force for flight
2. flexible not to break in strong wing
3. has veins for circulation of gases and strengthening the wing

Identifications of the sex of a cockroach

Structures on the ventral side of the last segments are used:

The male cockroach has styles while female cockroach has podical plates.

Functions of mouthparts of a cockroach

A table below shows the functions and adaptations of the mouthparts of a cockroach

Parts	Functions	Adaptations
Mandible	Cutting and masticating food	Strong and sharp edges
Maxillae	Cutting and chewing food	Have sharp edges
Maxillary palp	Taste food	sensitive to food, jointed for flexibility, hairy to increase sensitivity
labium	Taste food	Hairy to increase sensitivity

Economic importance of cockroaches

• Transmit germs from the toilets
• Their feces stain clothes
• Destroy document and clothes

Bee

Order: Hymenoptera

Characteristics of the order

1. have two pairs of membranous wings
2. have a waist between the thorax and abdomen
3. They live in colonies

Other characteristics of the bees

1. have hairy bodies
2. has segmented, smooth (without hairs) uniform-sized antennae.
3. Has a pair of compound eyes

Mouthparts

Consist of elongated proboscis tapering towards the apex, blunt-ended mandible; the labial pulp is segmented.

A drawing of the mouthparts of the bee

Thorax of a bee

1. Bears 3 pairs of legs
2. Has hymen between the thorax and abdomen
3. The  third pair of legs have the tibia deeply grooved to form a pollen basket that retain pollen

 

Abdomen

• abdomen constricts anteriorly to form  a waist but tapers at the posterior end
• the last segment has a sting
• it is hairy

Differences between a bee and a housefly

Bee	Housefly
2pairs of wings	One pair of wings
Lack halteres	Has a pair of halteres
The hind limb has pollen basket	Hind limbs lack pollen basket
Has enlarged /thickened tibia	Tibia shorter/not enlarged
Abdomen cuticle thickened/hardened	Abdomen cuticle thin
Has proboscis and mandible	Has only proboscis
Pointed proboscis	Expanded proboscis
Has sting on last segment of abdomen	Lacks sting
Has no simple eyes	Has simple eyes
Has tapering abdomen	Has rounded abdomen

 

Order: Isoptera

Characteristics of the soldier termite

– It has a massive enlarged head with

* prominent sharp mandibles for cutting food and defense.

* short segmented antennae.

* long segmented maxillary palps

– has a flattened body.

– has a smooth body without hair.

Economic importance

1. turns the soil over to keep it loose and aerated
2. source of food
3. destroy wooded properties
4. destroy plants

Worker termite

Order: isopteran

Characteristics

• Has biting mouthparts.
• Lack compound eyes.
• It has three pairs of legs.
• Has a rounded abdomen
• It’s dark for camouflage

Grasshopper

Order: orthoptera

– has threadlike antennae

– It has a pair of anal cerci.

Shape and appearance

The body is laterally flattened and tapering posteriorly.

Significance

• the lateral flatness enables the grasshopper to penetrate grass for hiding away from predators.
• The tapering nature makes the grasshopper streamlined.

Appearance

• some are green while others have shades of grey and brown for hiding.
• The exoskeleton is a waxy to reduce water loss.

The head

• It has big compound eyes for effective sight and wide field of view.
• Long antennae sense far objects.
• Has biting mouthparts for effective feeding.
• It has strong mandibles for cutting food and energy.

Adaptations of hind limbs to its function

1. muscles to create a repulsive force during movement
   1. jointed for flexibility
   1. long for quick movement
   1. areolium allow grip on a smooth surface
   1. craws enable the grasshopper to grip to the cracked surface
   1. spines pinch the enemy during the defense

Difference between the hind limbs of a bee and grasshopper

Hind limb of grasshopper	Hind  limb of a bee
No pollen basket	Has pollen basket
No pollen comb	Has pollen comb
Has spine	Has no spines
hairless	Has hairs
Thick and expanded femur	Has thin and short femur

Wasp

Order: hymenoptera

Characteristics

• has two pairs of membranous wings
• has a narrow waist between the thorax and abdomen
• has three main body parts; head, thorax, and abdomen.
• Dark-colored for camouflage

Sugar ant

Characteristics

• lack wings
• has three main body parts; head, thorax and abdomen
• has three pairs of legs
• has biting mouthparts
• has a thin waist between thorax and abdomen
• dark-colored for camouflage.

Mosquito

Classification

Kingdom          Animalia

Phylum             Arthropoda

Class:                Insecta

Order:               Diptera

Genus:              anopheles

Importance of mosquitoes

They transmit diseases.

Table showing diseases carried by mosquitoes.

Mosquito	Diseases	Causative organism
Female anopheles	malaria	plasmodium
Aedes	Yellow fever, dengue fever	Virus virus
Culex	Elephantiasis	Filarial worm

The life cycle of a mosquito

Mosquitoes undergo complete lifecycle

Control of malaria

• Sleep in a mosquito net
• Draining stagnant water
• Removing bush in and around the house
• Close the house to prevent entry of mosquitoes

Butterfly

Classification

Kingdom             Animalia

Phylum:              Arthropoda

Class:                   Insecta

Order:                  Lepidoptera

Genus:                 papilio

Importance

• Pollinate flowers
• Larva stage (caterpillar) are pest
• Larva stage harms human skin

Feeding: feeds on nectar using sucking mouth parts.

Lifecycle: undergo complete metamorphosis i.e. eggs → larva → pupa → adult,

Exercise

1. Which one of the following may not be used to classify insects

A. mouth parts

B. Feeding habits

C. structure of legs

D. Types of eyes

2. Which of the following fins provide major force of propulsion in fish?

          A. caudal

B. pectoral

C. Dorsal

D. Pelvic

3. Which of the following diseases is not transmitted by a mosquito?

     A. Malaria

     B. Yellow fever

     c.  elephantiasis

     D. cholera

4. Which of the following features belong to both Arachnida and Insecta.

A. cuticle and two pairs of wings

B. six pairs of legs and wings

C. Six pairs of legs and antennae

D. Jointed legs and cuticle

5. Which of the following is a respiratory organ in an insect?

          A. spiracle

          B. trachea

          C. Malphigian tubule

          D. zygote

6. Which of the following is a characteristic of insects only?

          A. Exoskeleton

          B. jointed legs

          C. two pairs of wings

          D. three body divisions

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Compiled by Dr. Bbosa Science