Download Arthropods

Lecture -17
Phylum Arthropoda
Arthropods
"arthropod" =
arthros - jointed,
podes - feet.
Arthropod Diversity
•
Arthropods make up over 75% of all living
organisms.
•
Over 1 million species have been described.
•
They are distributed aa over, in a range from
the shallow sea to mountain peaks.
•
They are the most successful animals on the
earth.
Arthropods
- Size range from microscopic insects and
crustaceans to the king crab(12 feet)
Parasites
Feed on plants
Predators
• They have an external skeleton (exoskeleton)
secreted by epidermis.
It is made up of protein (chitin) and lipids
Cilia are not present.
• Exoskeleton:
- Provides protection
- Support and locomotion.
- Prevents water loss.
• So, arthropods can live in too wet, too dry,
too hot, even too cold habitats.
• Arthropods are recognized by their jointed
appendages.
• Individual appendages have modified into
antennae, mouthparts, or legs.
- Jointed legs for more efficient locomotion
• Arthropod bodies are segmented.
1. Many segments.
2. Segments are fused together
into functional groups (tagmata)
- Eg. head or thorax of an insect
This fusing process is known
as tagmatization.
• All arthropods have a distinct head,
• sometimes fused with the thorax to form a
tagma called the cephalothorax.
Muscular system includes smooth muscles and
striated muscles as in chordates.
Movement of appendages is controlled by these
muscles.
Striated muscle
For quick action
Arthropods have a pair of compound eyes and
one to several simple eyes (ocelli);
A compound eye consists of hundreds or
thousands of lenses.
So, they can see a very wide angle of vision;
(can see even right behind them).
But are very short sighted.
• Arthropods are eucoelomate,
- coelom is much reduced.
•The body cavity is an open "hemocoel," (a space
filled loosely with tissue, sinuses, and blood).
• The circulatory system is open and
consists of a heart, arteries, and the open
spaces of the haemocoel.
• Respiration takes place through the body
surface, gills, tracheae, or book lungs.
• The nervous system is annelid-like.
- A brain and a double ventral nerve cord
• Most arthropods are dioecious (monosexual)
and have paired reproductive organs (ovaries,
testes).
• Fertilization is internal.
• Most lay eggs (oviparous).
• Arthropods grow by moulting their exoskeleton
(ecdysis).
• Development proceeds with some form of
metamorphosis.
(Atelocerata)
Class Symphyla
Sub phylum Chelicerata
• Examples;
Scorpions,
Spiders,
Ticks, and Mites,
Horseshoe crabs,
“Sea spiders"
Characteristics of Subphylum Chelicerata
1. Their body is divided into two regions (tagmata)
- cephalothorax (prosoma) and
- abdomen
(opisthosoma).
2. They do not have a distinct head
3. Cephalothorax contains six pairs of
appendages
4. Chelicerae are adapted for feeding
- to pierce the prey
- to tear apart the prey
5. Feeding habit – sucking liquid food from their prey
Class Merostomata
Diversity of Class Merostomata
•Only 5 species and 3 genera exist today.
Eg. Horseshoe crab, Limulus
•They are marine – burrow in mud near the shore.
• Feed on small invertebrates.
• They are nocturnal.
•Their geographical distribution is limited.
N. America
SE Asia
Indonesia
Characteristics of Class Merostomata
4. The pedipalps, resemble walking legs.
Function - walking
Mouth
Gnathobase
(to grind food)
Chilaria
(to crush food)
Last pair of walking legs
(to clean book gills)
5. Abdomen is broad.
It bears;
1. Genital operculum
2. Gill flaps (5 pairs)
(about 150 book gills inside them)
for respiration
Anus
Class Arachnida
Includes over 70,000 described species .
Examples ;
Spiders, scorpions,
Ticks and mites
•Arachnids are generally:
- aggressive,
- predatory,
- preying on small arthropods.
• Nearly all species are terrestrial.
• The prosoma is dorsally covered with a carapace.
Pedipalps are modified into grabbing & killing prey.
•They have simple eyes (Ocelli) .
Spiders
Spiders include 36,000 described species.
1. Cephalothorax and abdomen are
divided by a narrow stalk (pedicel).
2. Chelicerae bear
poisonous fangs.
Pedipalp
3. Coxal glands
for excretion
Walking legs
5. Spinnerets (silk glands)
for spinning silk
4. Abdominal appendages are
book lungs (for respiration)
Do not show external segmentation
Mites and ticks
• Around 10,000 species described.
Ticks are bigger but mites are microscopic.
• No external segmentation
• Cephalothorax and abdomen are fused
(Dorsally covered by carapace)
• Ticks have a false head( capitulum), carrying
mouth-parts.
Scorpions (1200 species):
The pedipalps are modified into large claws
Chelicerae are small.
Sting
Post-abdomen
Pre-abdomen
Pedipalp
Pseudoscorpions (2000 species),
Lecture 18, 19
Arthropods III, IV
Learning Outcomes
• Characteristic features and
diversity of Subphylum Crustacea
Subphylum Crustacea
Diversity
Approximately 45,000 species.
Crustaceans are the fourth most species group of
metazoans on earth, behind Insects, Mollusks, and
Chelicerates.
• Most are aquatic
- majority are marine
- some are found in fresh water
• Few on land.
• Crustaceans are the only arthropod group
that has primarily aquatic forms.
Crustaceans include;
•
Lobsters
• crabs
•
crayfish
• shrimp
And several other groups of organisms.
• Most crustaceans are free-living;
but some are sessile – Eg. Barnacles
A few are parasitic.
Suculina
• Crustaceans are:
– filter feeders
–active predators
–scavengers
Characteristics of Subphylum Crustacea
1. Body comprises of two tagmata.
- cephalothorax
- abdomen
2. Crustacean appendages are branched (biramous).
(primitive)
3. Crustaceans have 2 pairs of antennae.
a pair of antennule
a pair of antennae
•4. Crustaceans develop through a larval stage
called a nauplius larva.
1st antenna
2nd antenna
Mandible
Classification of Sub phylum Crustacea
Class Malacostraca
Class Branchiopoda
Class Ostracoda
Class Copepoda
Maxillopoda
Class Branchiura
Class Cirripedia
Class Malacostraca (Soft shell)
• Comprises about 24,000 described species.
• All body segments bear appendages
Typical malacostracan
Class - Malacostrata
Order
Decapoda
Isopoda
Amphipoda
Order Decapoda (Ten foot)
• This is the largest order of crustaceans
(10,000 species).
• First pair of walking legs are modified to
form pincers =Chelae (Cheliped).
Cheliped: help capture prey
(modified first walking leg)
•The eggs are retained by the females until they hatch into
free-swimming larvae.
Lobster
Crabs
Decapoda
• Crabs have a broader carapace.
• and a much reduced abdomen.
Hermit crabs They have adapted to live in snail shell.
Their abdomen lacks a hard exoskeleton.
King crab
Order Isopoda (Equal foot)
• They have no carapace.
• They are dorsoventrally flat.
Armadillidium
Some are found on Land
In moist places, – pill bugs
Armadillidium
Terrestrial wood louse
Some are parasitic on fish
Freshwater isopod -Sow bug
• Marine shallow-water isopods
Order Amphipoda (both side foot)
Beach hoppers
Gammarus
Similar to Isopods but laterally compressed.
Caprella -
Amphipoda
Class Branchiopoda
• Small to moderate-size crustaceans
• Primitive, aquatic, mainly freshwater
crustaceans:
• water flea
- Daphnia
• Brine shimp - Artemia
Water flea
Daphnia
branched antenna
• Minute freshwater crustacean, common in
temporary freshwater ponds.
• They move about like a flea by means of hairy
branched second antennae.
• The head is bent down towards the body.
• The rest of the body is covered by a laterally
compressed bivalve-like carapace (transparent –
large shield).
• Legs are paddle like
(respiratory gills)
Brine shrimp Artemia salina
No carapace.
The thorax consists 11pairs of
appendages.
Theyare filtratory;
By beating they propel the
animal forward and draw food
particles toward it.
They swim with their ventral
surface uppermost.
Telson
Salt water crustacean
• The eggs (cysts) are produced when their lake is
drying out (in high salinity).
• These eggs contain a "sleeping" embryo
which scientists believe survive up to 1000
years.
Cyst (egg)
Nauplius larva
Artemia live on Earth for 100 million years, so they
are colleagues of the dinosaurs.
• Artemia cysts - a commercial fish food
Class Ostracoda
(shell, mussel shrimp)
- Cypris
They are tiny marine and freshwater crustaceans
enclosed in a bivalve shell (carapace)
• They are zooplankton, living on the sea floor.
•Thoracic appendages reduced to two or none.
•They are mostly head.
Class Copepoda - Cyclops
- minute
- marine (majority) and freshwater crustaceans.
They have an elongated transparent body;
- large antennae
- Single median eye (nauplius eye)
- armoured exoskeleton
(but no carapace)
- a forked tail
Elongate body, tapers towards posterior end.
No carapace.
Four pairs of thoracic appendages-for swimming.
They are the dominant zooplanktons.
Class Branchiura
They are ecto-parasites of freshwater fishes.
Broad shield like carapace.
No gills.
Compound eyes are present
Four pairs of thoracic appendages.
Abdomen reduced.
Mouth appendages modified as Sucking cups.
Argulus (fish louse)
Class Cirripedia
Barnacle- (900) species
• Adult forms a hard calcareous shell.
• They remain attached to submerged surfaces, - rocks , ships’ or boat’s bottoms
Acorn Barnacles (Balanus)
Tiny particles of food trap by cirri.
Cirri - feathery retractable organs (thoracic appendages)
Cirri emerge from openings between the shell plates.
Adult barnacles are hermaphrodites.
Parasitic barnacles - Saculina
Saculina - branches through the tissues of its host
(the common shore crab) .
It produces only large brood-sac externally under
the host's abdomen, containing its many eggs.
Pill bugs Armadillidium
Gammarus
Caprella
Cyclops
Lecture - 20
Arthropods V
Subphylum Uniramia (Atelocerata)
• The largest and most varied arthropod group.
• Uniramians are characterized by;
1. Presence of modified appendages located at the
edge of the mouth - (mandibles)
- Mandibles are used as jaws.
2. Presence of one pair of antennae.
3. Presence of Uniramous appendages.
• Subphylum Uniramia (Atelocerata)
Class Diplopoda
Class Chilopoda
Myriapoda
Class Hexapoda (Insecta)
Myriapods
• Include; centipedes and millipedes.
• Their bodies are made up of many segments.
• They live in moist micro-habitats.
Class Chilopoda - Centipeds
Over 2500 species.
Body segments are flattened.
Each segment bear a pair of appendages (legs).
The appendages of the first body segment
modified to poisonous fangs - to capture prey
• Centipedes are predatory, feeding on soil
invertebrates .
• They run fast to escape from danger.
•The young ones resemble miniature adults.
Class Diplopoda - Millipeds
• Body segments are cylindrical.
• Each segment bear two pairs of legs. Except first
four segments each bear a single pair of legs.
• Millipedes lack poisonous fangs and do
not bite.
• They live on decaying plant and animal
matter.
• They are slow movers.
10, 000 described species are Millipeds – bio indicators
Class Hexapoda - Insecta (insects)
Insects include a great majority of the species of
animals on earth.
- one million named species (100,000)
- several millions unnamed.
They are the most successful group of animals.
• Insects are found in almost all terrestrial
and freshwater habitats;
- from deserts to freshwater ponds
- from tropical rainforest to the arctic wastes
- A few marine
Their feeding habits are varied.
- Phytophagous (herbivores)
- Omnivores
- Predators
- Parasitic
• Insects show huge variety in shape and
form.
- but they do not have very large body size.
Characteristics of Insects
• Insect body wall is a Chitinous cuticle.
• Thin epicuticular layer (wax layer) highly
resistant to water and other solvents.
• Insect body divides into 3 tagmata;
- head,
- thorax and
- abdomen
Each tagmata composed of several smaller segments.
Insects (in=into, sect=cut)
• Insects are morphologically divided
into two groups.
– Wingless insects (Subclass Apterigota)
– Winged insects (Sub class Pterigota)
Most insects have wings.
Wings are found on the 2nd and 3rd thoracic segments.
(10 segments)
Each thoracic segment contains a pair of legs.
Abdomen (10 segments)- No appendages
Head appendages are modified for feeding
(mouthparts).
Thoracic appendages
Insects have different life cycle patterns
It is an important characteristic of insects.
1. Eggs on hatching produce miniature adults.
Direct development (Ametabolous)
Wingless insects
Silverfish
2. Newly hatched young (larva) are completely
different in appearance from adults.
These larval forms
- live in different habitats,
- eat different foods,
Reduce competition
The larva feeds and grows. It
molts periodically.
Become non-feeding encased
pupa.
Pupa undergoes a complete
transformation to a fully-formed
adult emerges ("metamorphosis“) .
"holo-metabolous."
3. The newly hatched young (nymphs) are more
similar to the adult;
but small in size,
lack wings,
sexually immature.
They undergo a more gradual
process of development to
become adults.
"hemi-metabolous."
Hemimetabolous Insects
Order Odonata
Dragonfly
Order Orthoptera
Cricket
Grasshopper
Order Isoptera
Termites
Order Hemiptera
Water bug
Order Homoptera
• Aphid
Order Blattodea
Cockroach
Order Phasmida
Walking leaves
Stick insect
Order Mantodea
Praying mantis
Adult
nymphs
Egg case
Holometabolous insects
Order Coleoptera
Beetles
Pupa
Larva
Eggs
Order Lepidoptera
Butterfly
Wings cover with scales
Moth
Order Diptera
Mosquito
Housefly
Order Hymenoptera
Ant
Wasp
Ant
Insect Feeding habits are varied
• Insect mouthparts are modified for their
feeding habits.
• Most of the insects are plant feeders.
• Mouthparts are used to grind their food or
suck as a juice and move it toward the
back of the mouth.
Grasshopper – chewing and biting
Mouthparts are modified for feeding on plant parts.
• Mandible well developed
Plant bugs and mosquitoes - Piercing-Sucking
• Mouthparts are modified to a needle like stylet. It is
used to suck blood/plant juice.
• Labium serves also as a food canal.
stylet
Labium
Moths and butterflies - Siphoning
When feeding the proboscis is uncoiled and
extended.
Nectar is sucked up into the mouth or oral cavity.
House fly - Sponging
Proboscis is the two soft lobes with
many small tubules.
When feeding saliva are pumped
onto the food through the probosis.
Mouth
opening
The dissolved food then moves by
capillary action of sponge and
ingested.
Honeybees - Chewing-Lapping
Mouthparts are modified to utilize honey
and nectar.
- to cut floral tissue to gain access to nectar,
- for defense, and
-for manipulating wax.
Mouthparts forms a flexible and contractile
tongue covered with hairs.
It draws liquid into the body by slowly
moving it back and forth.
• The legs of many insects are specially
adapted to the insect's mode of life.
Grasshopper – Hind leg
Jumping
Femur enlarged
Head louse - Clinging
Mole cricket - Digging/burrowing
• Mole crickets - front legs - modified for
digging in the soil. Resembles a shovel
(broaden).
Honeybee
The first leg
notch – clean legs, antennae
The hind leg Inside
Curved rows of hairs
( pollen basket)
Praying mantis - Raptorial/grasping