Presentation: Invertebrate Zoology
Phylum Arthropoda
TABLE OF CONTENT
General
Introduction
Characteristics
Anatomy and
Morphology
Nutrition
Excretion
Reproduction
Locomotion
Nervous
system
Classification
Importance
General Introduction
• Phylum Arthropoda is a highly diverse animal group
• Diversity and success: segmented body, hard exoskeleton, and jointed
appendages
• More species and more individuals than all other groups
• Find: land, oceans, rivers, lakes, mountains, hot springs, you name it.
• Appendages: ting, feeling, sensing, mating, respiring, walking, or defense.
• Chitin is the main component in exoskeletons.
• Crabs and barnacles, secrete calcium carbonate into their exoskeleton, making
it thick and hard.
• Includes: spiders, grasshoppers, beetles, butterfly, termites, shrimps, ant etc.
Evolutionary
History of
Arthropods
• Arthropods are monophyletic placed within a
clade of molting animals, the ecdysozoans.
• The earliest fossils from Cambrian explosion
(535–525 million years ago)
• Lobopods, an extinct group from which
arthropods may have evolved.
• The earliest stem-group arthropods and they are
worm-like animals with annulated appendages.
• As arthropods evolve, the segments tended to
fuse and become fewer, and the appendages
became specialized for a variety of functions
• They also share many features with the phylum
Annelida.
How did they evolve the segmented body?
Genetic changes:
• Have two unusual Hox gene.
• Researchers studied Hox genes in
onychophorans
• The evolution of body segment may have
been driven by changes in the sequence
or regulation of existing Hox genes.
Characteristics of Arthropods
Presence of jointed legs
Body is divided into head, thorax and abdomen
Bilaterally symmetrical and triploblastic
• organ system level of organization.
• chitinous exoskeleton.
• have compound eyes.
• well-developed central nervous system.
• digestive tract is complete
• open circulatory system with dorsal heart and arteries.
• Respiration: body surface or by gills and trachea or book lungs
• Sexes are separate and sexual dimorphism is exhibited
Anatomy and Morphology of Arthropods
• Segmented bodies: head, thorax, and abdomen.
• Chitinous exoskeleton
• Ectotherms: they cannot produce their own body heat, relying on the
environment for temperature regulation.
• strong sense organs, making them very responsive to changes in their
environment.
• Compound eyes (think of flies or spiders)
• Antennae
• Setae: tiny hairs covering the body that act as touch or taste sensors
Head
Thorax
Abdomen
Spiracles
Coxa
Trochanter
Femur
Tibia
Tarsus
Genitalia
Wings
Nutrition in Arthropods Arthropods
• Some are specialists upon one food source
• some are generalists, exploiting varied sources.
• Some are herbivorous: scrape, chew, or suck on plants, eat the pollen, nectar,
fruit, or woody components.
• Spiders are predators, capturing and consuming insects.
• Some arthropods are parasitic
• Crustaceans are often opportunistic eaters, will scavenge, or live off algae;
• Others, like woodlice, are detritivores, eating mostly dead plant matter.
• Some eat feces, like dung beetles.
Digestion in Arthropods
• Depending on their nutrition, arthropods have mouthparts that
assist them catch and consume prey.
• Food enters the mouth, travels through the foregut (pharynx and
esophagus), and finally reaches the midgut.
• Digestive enzymes are produced there, which aid in the digestion
and absorption of food.
• Extracellular digestion takes place
• Have Complete digestive system
Excretion in Arthropods
• There are two different excretory systems used by members of the
Arthropoda phylum:
• Aquatic arthropods eliminate ammonia through permeable membranes,
particularly gills.
• Myriapods, insects, and some arachnids use the Malpighian tubule
system to filter uric acid, and other nitrogenous waste out of the blood
and in the hemocoel.
• These waste products are deposited into the hindgut and then expelled as
feces.
• Most aquatic arthropods and a few terrestrial also contain nephridia to
extract other wastes for excretion as urine.
Water Balance In Arthropods
• Both arachnids and insects possess waxy compounds in the
epicuticle:
• Reduce water loss,
• water repellent,
• water striders to move over water.
• Arthropods that lack a waxy epicuticle live in leaf mold and soil,
beneath logs, under stones, and in other areas where the danger of
desiccation is reduced.
Reproduction In Arthropods
• Sexes are separate in arthropods
• Few are hermaphroditic
• Some methods of reproduction:
1. Parthenogenesis
2. Viviparity
3. polyembryony
Sexual Reproduction
• Sperm are commonly transferred to the female within sealed packets
known as spermatophores
• In scorpions, pseudo scorpions, and some mites, the stalked
spermatophore is deposited on the ground.
• The female is attracted to the spermatophore chemically
• Also, the male maneuvers the female into a position in which she can
take up the spermatophore within her genital opening.
Locomotion In Arthropods
1.
Jointed appendages
2.
Hard exoskeleton
3.
Fast acting striated muscles attach to the inside of the skeleton
• These act together as a lever system for movement.
• Appendages of arthropods have been adapted for all types of locomotion:
• walking, pushing, running, swimming, and burrowing.
• Some have wings that enable them to fly especially in insects.
The Nervous System
• Developed nervous system
• Nervous system composed of ganglia
• Ganglion: A dense group of interconnected neurons.
• Have developed: Brain, ventral and ganglionated longitudinal nerve cord, and lateral
nerves
• In grasshoppers, the brain is divided into three regions:
• Protocerebrum: Vision control from ocelli
• Deutocerebrum: Process sensory information from antenna
• Tritocerebrum: Integrate sensory inputs and connect ventral nerve cord.
Classification Of Arthropods
There are five main classes
1. Class Crustacea
2. Class Chilopoda
3. Class Diplopoda
4. Class Insecta
5. Class Arachnida
Class Crustacea
• Mostly aquatic
• Body: cephalothorax and abdomen
• Two pairs of antennae
• Four pairs of jointed appendages
• Gills for respiration
• Calcareous skeleton
• Cephalothorax is covered by carapace
• Pairs of stalked eyes
• Separate sexes
• E.g., River prawn, crab, crayfish, lobster.
Class Chilopoda
• Body flattened dorsoventrally
• Have a pair of leg in each segment
• Have trachea for gaseous exchange
• Have a pair of poisonous claws
• They are mainly terrestrial
• Have simple/ compound/ no eyes.
• E.g., centipede.
Class Diplopoda
• Have cylindrical / round body
• Have one pair of antennae
• Have two pairs of legs on each segment
• Has no poison gland
• Gaseous exchange is by trachea
• Examples: millipede
Structural Differences Between Millipede and Centipede
Millipede
Centipede
Has cylindrical / round body
Has flattened body
Has two pairs of legs on each segment
Has one pair of leg each segment
Has no poison gland
Has a poison gland
Has short antennae
Has long antennae
Class Arachnida
• Body divided into two parts:
• Cephalothorax and Abdomen
• Four pairs of jointed legs
• Have simple eye
• Have pedipalp
• Mostly terrestrial
• Gaseous exchange is by lung-book
• Ex: spider, scorpion, mites, ticks
Class Insecta
• Body divided into three parts: Head,
thorax and abdomen.
• Three pairs of jointed legs
• Exoskeleton made up of chitin
• A pair of compound eye
• Undergoes metamorphosis
• Has: claws, wings
• High reproductive rate, metabolic rate
• Ability to fly
• Ex: Cockroach, Housefly, Cotton
Stainer, Butterfly, Termite
Metamorphosis
Definition:
Series of gradual changes in structure / forms that occur during the
development of organisms especially insects from egg to the adult
stage.
Types of Metamorphosis:
1. Complete metamorphosis
2. Incomplete metamorphosis
Complete Metamorphosis
• This is the series of changes which
take place in insects from:
1. Fertilized egg to Larva
2. Larva to Pupa
3. Pupa to Adult stage
• Examples: housefly, mosquito,
bees, grain weevil, butterfly.
Incomplete Metamorphosis
• The series of changes in insects
which takes place from:
1. Fertilized egg to Nymph
2. Nymph to Adult
• Nymph differ from the adult stage
because: smaller size and un-matured
reproductive organs.
• Examples: Grasshopper, Aphids,
Cockroach, Locusts etc.
Importance Of Arthropods
1. Food: Many Species of Crustaceans like crab, lobster
2. Pest control: mites to prey on unwanted arthropods on farms
3. Ecological Roles: Mites, ticks, centipedes, and millipedes are
decomposers.
4. Pollinators: Insects like honeybee
5. Vectors: Host pathogens like mosquito
THE END!!!!!
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