Phylum Arthropoda (Jointed Appendages
Animals)
MAIN CHARACTERS
§ Arthropoda is the largest Phylum of the animal kingdom including
10, 00000 species of different types of animals.
§ The word Arthropods is derived from Greek Arthos – Jointed and
Podos – Foot.
HABIT AND HABITAT
Arthropodes have
undergone an adaptive radiation for aerial, aquatic, terrestrial and parasitic
environment. They are widely distributed in each and every place of the world.
NATURE
Arthropoda are
“bilaterally symmetrical,” metamerically segmented metazoa.
EXTERNAL FEATURES
§ Their body is covered by an exo-skeleton of “chitin” and
protein.
§ They possess paired jointed appendages.
§ Their metamers are not alike but are specialized and their
number is generally fixed.
§ The head is well developed.
INTERNAL FEATURES
§ Musculature is not continues but comprises separates striped
muscles.
§ The coelomic space in Arthropods is occupied by the blood
vascular system and is thus called “Haemocoel.”
§ Digestive tract is complete; mouth and anus lie at the opposite
end of the body.
§ Circulatory system is open with dorsal heart and arteries but
without capillaries.
§ Respiration through general body surface, by gills in aquatic
forms, trachea or book lungs in terrestrial forms.
§ Excretion by “Malpighian tubules” or Coelomoducts.
§ Sexes are generally separate and sexual dimorphism is often
exhibited by several forms.
§ Fertilization is internal.
§ Development is usually indirect through the larval stage.
§ Nervous system of arthropods is quite similar to that of
annelids and consists of dorsal anterior brain and a double ventral nerve cord.
CLASSIFICATION OF ARTHROPODA
Phylum Arthropoda
is divided into following five classes:
1. CLASS MEROSTOMATA
§ Almost all members of the class Merostomata are extinct. The
only living merostomes, the king Crabs have survived.
§ The animals are horse-shoe shaped.
§ The long spike like tail that extends, posteriorly is used in
locomotion. It is called “Telson.”
§ They feed on mollusks, worms and other invertebrates that they
find on the ocean floor.
§ King Crabs a hors-shoe crabs have a tough “Carapace” jointed to
a smaller abdomen.
§ E.g:Limulus Polyphemus (King Crab).
2. CLASS ARACHNIDA
§ This class includes spiders, scorpions, mites, ticks and many
other terrestrial arthropods.
§ The Arachnid body consists of a cephalothorax and abdomen.
§ Cephalothorax is comprised of fused head and thorax.
§ Arachnids have six pairs of jointed appendages.
§ Most Archnids are carnivorous and prey upon insects and other
small arthropods.
§ Respiration in archnids takes place either by trachea or book
lungs or by both.
§ They are mainly terrestrial arthropods.
§ They have no antenna.
§ Cephalothorax is non-segmented.
E.g: Scorpions,
Ticks & Mites, Spiders
3. CLASS CRUSTACEA
§ They live both in marine and fresh waters.
§ A few are terrestrial.
§ Crustaceans are unique among arthropods in possessing two pairs
of antenna.
§ They always have one pair of mandibles and two pairs of maxillae
around the mouth.
§ Mandibles are usually adapted for biting and chewing. Maxillae
are used for holding the food.
§ Their body is divided into three distinct parts, i.e. the head,
thorax and abdomen.
§ Respiration usually takes place through gills associated with
appendages.
§ The sexes are usually separate and the reproduction is sexual.
§ The thoracic and abdominal appendages may be variously modified
for walking, swimming, feeding, respiration or as accessory reproductive
structures.
E.g: Sacculina
(Parasitic Crustacean), Astacus (Cray-fish), Prawns, Shrimps, Lobsters and
Crabs etc.
4. CLASS MYRIAPODA
§ All the animals are terrestrial.
§ Their body is divided into a head and an elongated trunk with
many segments.
§ Each segment bears one or two pairs of legs.
§ They are carnivorous /herbivorous.
§ Eyes may present or absent.
E.g: Millipedes and
Centipedes etc.
5. CLASS INSECTA (HEXAPODA)
§ Insecta is the largest class of the animal kingdom.
HABIT AND HABITAT
§ In their adaptive radiation, approximately a 8,50,000 species of
insecta have occupied all types of terrestrial habitat.
§ Some live in fresh water, however one small group is marine.
NATURE AND ADAPTATIONS
§ The great success of insects can be attributed partly to the
development of flight in them.
§ Flight has provided them the great capacity of dispersal, access
to food sources, and favorable habitat and escape from enemies.
§ Corresponding to their number of species, there exists a huge
variation in their structural and biological adaptations.
EXTERNAL FEATURES
§ All insects have their body divided into three well-defined
regions i.e. the head, thorax and abdomen.
§ There is always a pair of antenna on the head.
§ The thorax always consists of three segments:
(a) Prothorax
(b) Mesothorax
(c) Metathorax
(b) Mesothorax
(c) Metathorax
§ Each thoracic segment bears a pair of legs.
§ Head consists of six fused segments and a pair of compound eyes
and mouth parts.
§ Abdomen comprises 7-11 segments and devoid of appendages.
MOUTH PARTS
The feeding appendages consists of three pairs:
(a) Mandibles
(b) First Pair of Maxilla
(c) Second Pair of Maxilla
The feeding appendages consists of three pairs:
(a) Mandibles
(b) First Pair of Maxilla
(c) Second Pair of Maxilla
§ The second pair of maxillae have fused together to form the
“LABIUM,” or lower lip
§ The upper lip is formed by the projections head and is called
the “LABRUM.’
Types:- The mouth appendages have been greatly modified to form five
basic types of pattern:
(i) Biting
(ii) Chewing
(iii) Piercing
(iv) Sucking
(v) Siphoning or Sponging
(i) Biting
(ii) Chewing
(iii) Piercing
(iv) Sucking
(v) Siphoning or Sponging
INTERNAL FEATURES
§ Heart is elongated, tubular and divided into chambers situated
in the abdomen.
§ Excretion takes place through “Malpighian tubules.”
§ Liver is absent but salivary glands are usually present.
§ Respiration is by “TRACHEA”. External gills may be present as
accessory respiratory organs in some aquatic insects.
REPRODUCTION
Reproduction is sexual in most insects. However it takes place parthenogenetically i.e. eggs developing without being fertilized by sperms in a number of insects e.g: Aphids and Termites etc.
Reproduction is sexual in most insects. However it takes place parthenogenetically i.e. eggs developing without being fertilized by sperms in a number of insects e.g: Aphids and Termites etc.
METAMORPHOSIS
§ The development of insects after hatching from egg into adult
stage involves considerable growth and in some cases drastic morphological
changes.
§ The entire post-hatching development is termed as
“Metamorphosis.”
(A) INCOMPLETE METAMORPHOSIS
§ In some insects the immature form that hatch from the egg are
essentially similar in shape to their adults, but are smaller in size, lack
wings and reproductive organs
§ They attain adult characters after some growth period. This type
of metamorphosis is called “Incomplete Metamorphosis.”
§ Three stages are Egg → Nymph → Adult.
For example
Cockroach, Grasshopper, Bugs etc.
(B) COMPLETE METAMORPHOSIS
§ In this type the animal shows following stages during its
complete development: Egg → Larva → Pupa → Adult.
For example
Mosquito, Butter fly, House fly etc.
ECONOMIC IMPORTANCE OF INSECTS
Insects are of very
great importance to man.
BENEFICIAL INSECTS
1. Apis, the honey bees produce honey and also give wax.
2. Insects bring about the cross-pollination.
3. Bombyx and Eupterote are silk-moths and produce silk.
4. The larvae of Lucilla and Pharmia are used in wound healing of bones.
5. Some insects feed upon and destroy harmful insects.
6. Some insects are Scavengers
1. Apis, the honey bees produce honey and also give wax.
2. Insects bring about the cross-pollination.
3. Bombyx and Eupterote are silk-moths and produce silk.
4. The larvae of Lucilla and Pharmia are used in wound healing of bones.
5. Some insects feed upon and destroy harmful insects.
6. Some insects are Scavengers
HARMFUL INSECTS
1. Many types of mosquitoes, flies, fleas, lice and bugs transmit diseases to man and animals.
2. Human food is spoiled by cockroaches, ants and flies.
3. Tinea and Teniola are cloth-moths and destroy cloths.
4. Tenebrio is mealworm. They eat meal, flour and grains.
5. Lepisma destroy the books.
6. Termites destroy books and wood.
7. Many insects injurious to crops e.g. Tree hoppers, Leaf hoppers, Aphids, White flies and bugs.
1. Many types of mosquitoes, flies, fleas, lice and bugs transmit diseases to man and animals.
2. Human food is spoiled by cockroaches, ants and flies.
3. Tinea and Teniola are cloth-moths and destroy cloths.
4. Tenebrio is mealworm. They eat meal, flour and grains.
5. Lepisma destroy the books.
6. Termites destroy books and wood.
7. Many insects injurious to crops e.g. Tree hoppers, Leaf hoppers, Aphids, White flies and bugs.
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