current problems of pakistan

Topics: Arthropod, Spider, Arachnid Pages: 16 (1126 words) Published: April 21, 2014
Characteristics of the Phylum
Arthropoda
The segmented bodies are arranged into
regions, called tagmata (e.g., head, thorax,
abdomen).
The paired appendages (e.g., legs, antennae)
are jointed.
They posses a chitinous exoskeletion that
must be shed during growth.
They have bilateral symmetry.
The nervous system is dorsal (belly) and the
circulatory system is open and ventral (back).

Arthropod Groups (taxa)
The arthropods are divided into two
large groups that exist today:
The Chelicerates
and
The Mandibulates

Exoskeletons
• Strength and
impermeability
• Solves difficulties of
life on land:
– desiccation
– need for structural
support

• BUT: must molt to
grow (ecdysis)
Grasshopper molting

Phylum Arthropoda “arthropods”
• > 1 million spp., most of them insects (most of those,
beetles)
• Most diverse, widely distributed & abundant of all
animal phyla

Arthropod innovations
• Exoskeleton of chitin
* Hard & strong
* Impermeable to water
* Molting

• Segmentation
• Jointed appendages

Millipede

* “jointed feet”
• efficient walking &
swimming

* wings in most
• one of 2 phyla to fly
Monarch butterfly metamorphosis

Arthropod limbs
• Two types, relating to feeding mode
* Uniramous, single branch
* Biramous, two branches, sometimes gnathobasic
(like in Limulus and the trilobites)
* Some doubt cast recently on this simple scheme!

Trilobite gnathobasic limbs

Further arthropod anatomy
• Extensive cephalization (sense organs & mouth parts)

• Well developed



sense organs:
* “Taste”
* Sight many
with complex,
compound
eyes
Segment fusion

Abdomen
Antennae
(sensory
reception)

Head Thorax

Swimming
appendages

Walking legs
Pincer (defense) Mouthparts (feeding)

Some Arthropod groups

Trilobite (extinct group)

Limulus

Millipedes
and
centipedes

Class Arachnida
“Spiders, mites, ticks, scorpions”

50 µm

• 6 pairs of appendages
• including 4 pairs of walking legs

Class Crustacea
“Crabs, shrimp, barnacles”
Lobster

Goose-neck barnacles

• Mostly
marine
• Carnivores,
detritivores,
filter feeders
• 2 pairs of
antennae
• 3 or more
pairs of
mouthparts
• 3 or more
pairs of legs
Shrimp on coral

Cf Fig 33.38

Classes of Crustacea
(mostly marine, fresh water, a few terrestrial)
(all have two pair of antennae, five or more pairs of legs,
segmented abdominal appendages, head & trunk or
cephalothorax & abdomen body arrangement, have gills)

Isopoda - sowbugs or pillbugs
Amphipoda - sand fleas, amphipods
Cirripedia - barnicles
Decapoda - crabs, lobster, shrimp
several other minor orders

Crayfish cephalothorax
(Decapoda)

Sowbug (Isopoda),
a terrestrial crustacean

Class Insecta - Insects
Fig 33.35



Fused segments into 3
body regions:
* Head
* Thorax
* Abdomen




Metamorphosis
Flight




26 Orders
By numbers and
influence, the most
important phylum of
organisms

Chelicerate Arthropod Characters:
Pincher-like mouthparts chelicerae - and pedipalps
NO antennae
Two body regions, usually cephalothorax & abdomen
Four pairs of legs
Horseshoe crabs and arachnids
are only living groups

Mandibulate Arthropod Characters:
Mouthparts are mandibles normally chewing sideways
One or two pairs of antennae
Various body region arrangements cephalothorax & abdomen / head & trunk / head, thorax & abdomen
Variable leg numbers
Insects, crustaceans & myriapods

Orders of Arachnids
Scorpionida - scorpions
Pseudoscorpionida - false
scorpions
Opiliones - daddy-long-legs or
harvestmen
Acari - mites & ticks
Araneida - spiders

Pseudoscorpion
Scorpion

Daddy-long-legs

Tick
(a mite)

Wolf
Spider

Scorpion Anatomy

chelicerae

eyes

pedipalp

Pseudoscorpion

Mite and Tick Body Regions
pedipalps &
chelicerae

cephalothorax

abdomen

American dog tick male

Blacklegged (deer) tick female

American dog tick...
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