Largest Phylum of Kingdom Invertebrata is phylum Arthropoda, they have a segmented body, jointed limb and a hard shell on their body.
Kingdom Invertebrata (Arthropoda):
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- Those livings creatures which have no back bone or vertebral column in there bodies are called invertebrates.
- There are so much Invertebrates living on earth, some have cartilage (soft bone) in there whole body or some parts and some are boneless.
- Biologists have made a category in which there are only Invertebrates. It is called Kingdom Invertebrata .
- In this kingdom there are over thirty/30 phyla (plural of Phylum).
- {*Phylum = It is a level of classification or taxonomic rank below kingdom and above class.
- The largest phylum of Kingdom Invertebrata is known as Phylum Arthropoda.
- Probably 84% of all known species of animals are members of this phylum.
- Animals which have jointed appendages/legs belong to Phylum Arthropoda.
Phylum Arthropoda:
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- There are over one million described species of Arthropods living on earth.
- Researchers have estimated that the total number of living arthropods may will exceed to 30 million species.
- Arthro means jointed and Poda means foot.
- Animals belongs to this phylum are bilaterally symmetrical .
- {*Bilateral Symmetry =The property of being divisible into two equal (mirror) halves on either side of a unique plane.
- These have jointed appendages/legs, exoskeleton and a segmented body.
- Segmented body means their bodies are divided into various parts and these segmented parts are arranged along the anterior-posterior axis.
- A large number of arthopods consists of insects.
- They have well-differentiated organs and an organ system.
- Arthropods have an open circulatory system unlike vertebrates. Vertebrates have close circulatory system.
- {*open circulatory system= A system in which the blood is not enclosed in the blood vessels, but is pumped into a cavity called a hemocoel.
- Examples of Phylum Arthropoda are – Spiders, Butterflies, Grasshoppers, Wasps and Mosquitoes.
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Characteristics of Arthropods:
- Arthropods live in every habitat on Earth and show a great variety of adaptations.
- Cilia is absent, Coelom is greatly reduced; nervous system consists of dorsal brain.
- Eggs of arthropods are typically rich in yolk.
- Arthropods are characterized by their jointed appendages/limbs and Cuticle made of Chitin.
- {*Cuticle = A tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provides protection to organism or organ.
- {*Chitin = An intense, defensive and semitransparent polysaccharide, that frams the main segment/component of arthropod exoskeletons and the cell walls of certain fungi.
- A body of an arthropod consists of segments, each part have a pair of limbs/appendages.
- Arthropods do the process of Moulting or sloughing.
- {*Moulting = The process in which shedding of the old exoskeleton/shell takes place, to let the organism grow.This process is also called ecdysis.
- The new exoskeleton is initially soft but hardens after the moulting of the old exoskeleton.
- Their heads are made-up of fusion of varying numbers of segments and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus.
Reproduction in Arthropods:
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- A few arthropods, such as barnacles. These are hermaphrodites/bisexual.
- {*Hermaphrodite = A single individual, having both male and female sex organs .
- Arthropods of most species remain of one sex their entire lives (most of them are not hermaphrodites).
- A few species of crustaceans and insects reproduce asexually. Particularly if conditions favor a "population explosion".
- When conditions become less favorable then they revert to sexual reproduction .
- Most arthropods perform/do sexual reproduction (No matter what condition it is) .
- Arthropods that live in water can breed by external fertilization ( for example frogs) and by internal fertilization (e.g Mammals).
- All terrestrial (live on land) arthropods use internal fertilization.
- To transfer the sperm directly to the female, some arthropods ( e.g Opiliones , millipedes and some crustaceans) use modified appendages such as penises or gonopods.
- However, most male terrestrial arthropods produce spermatophores (Waterproof packets of sperm). Females take those pockets into their bodies.
- Most arthropods lay eggs and are known as oviparous.
- Some of them are ovoviparous, like scorpions are ovoviparous:
- {*Ovoviparous = Organisms that produce their babies after the eggs have hatched inside the mother.
Growth and Development:
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- Before reaching to adulthood, most arthropods go through one or more larval stages. This process is called metamorphosis.
- There two types of metamorphosis (e.g Complete and Incomplete metamorphosis).
- Complete metamorphosis and incomplete metamorphosis are two growth types of insects where the body structure of insects changes during their lifecycle.
- Both complete and incomplete metamorphosis extend from the egg stage to the adult/grown-up stage.
< Complete metamorphosis >
- Complete metamorphosis consists of four stages: Egg , Larva , Pupa and Adult.
- During complete metamorphosis, insects look different at each stage of growth and development.
< Incomplete metamorphosis >
- A type of metamorphosis in which an insect hatches from an egg and then goes through several nymphal stages.
- Incomplete metamorphosis consists of three stages: egg, Nymph, and adult.
- {*Nymph = Young stage of insects that is similar to the adult except that wings are not fully developed.
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Sub-Phyla of Arthropoda:
- The Phylum Arthropoda includes a wide range of species, that are divided into the subphyla of extant forms and some sub-phyla have classes.
Hexapoda (insects and springtails).
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- The largest number of species of arthropods are in this sub-phylum.
- It includes the insects as well as three much smaller groups of wingless arthropods (springtails) :
- (Class: Protura)
- (Class: Collembola)
- (Class: Diplura)
Crustacea (crustaceans).
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- There are ten classes :
- (Class: Cephalocarida)
- (Class: Branchiopoda)
- (Class: Ostracoda)
- (Class: Copepoda)
- (Class: Mystacocarida)
- (Class: Remipedia)
- (Class: Tantulocarida)
- (Class: Branchiura)
- (Class: Cirripedia)
- (Class: Malacostraca)
Myriapoda (millipedes and centipedes).
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- Subphylum Myriapoda is divided into four classes:
- (Class: Chilopoda)
- (Class: Symphyla)
- (Class: Diplopoda)
- (Class: Pauropoda)
Chelicerata (arachnids).
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- There are three existing classes within the phylum:
- (Class: Arachnida)
- (Class: Xiphosura)
- (Class: Pycnogonida)
Trilobitomorpha (trilobites).
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- Subphylum Trilobitomorpha consists of a single Class.
- (Class: Trilobita)
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