To study the classification with reasons of the phylum Arthropoda.

Title:- To study the classification with reasons of the phylum Arthropoda. 

Phylum Arthropoda :- Arthopods means jointed legs (Greek; arthos- jointed, Podos - Foot or legs] therefore jointed, legs is the most important characteristic structure of this phylum.

General characters of Arthropods:- 

(1)The animals are bilaterally symmetrical and metamerically segmented. 

(2)The body is covered externally by thick, tough, non-living organic chitinous exoskeleton.

(3)Exoskeleton is cast off periodically & this process is Called ecdysis or moulting. It is essential for the growth of the animals.

(4)The appendages are jointed & they are modified as gills, jaws, legs, etc. for various functions.

(5)They are triploblastic animals but true coelom is reduced in adult & represented by excretory & reproductive organs.

(6)Respiration may occur throughout the body surface but generally takes place by special structures like gills, tracheae & book lungs.

(7)circulatory system is of open type i.e. the blood flows in spaces or sinuses comprising haemocoel instead of blood vessels. 

(8)True nephridia are absent. Excretion by green gland or by malphigian tubule.

(9)Nervous system is of annelidian type.

(10)Compound eyes are present. 

(11)Sexes are usually separate & often there is distinct sexual dimorphism. 

(12)Fertilization is generally internal. Development includes larval forms which undergo varying degree of metamorphosis to become adult.

Phylum Arthropoda divided into five class:-

1)Crustacea - e.g. Crab

2)Myriapoda - e.g. Millipede 

3) Insecta - e.g. Cockroach

4) Arachnida - e.g. Scorpion

5) Onychophora - e.g. Peripatus 

Description:- 

1]Class: Crustacea: Carcinus [crab]

Phylum: Arthropoda - Jointed appendages.

Class: crustacea-  Thick exoskeleton, head and Thorax fused.i.e. Cephalothorax. 

Sub-class: Malacostraca: Abdomen devoid of caudal style eyes usually stalked. 

Order: Decapoda - Ten legs are present. 

Genus: Carcinus. 

Species: meanus 

2]Class: Arachnida - Palamnaeus [scorpion]

Phylum: Arthropoda - Jointed appendages. 

Class: Arachnida- Air breathing, terrestrial, four pairs of legs.

Order: Scorpionidea - Body divisible into prosoma, mesosoma & metasoma.

Genus: Palamnaeus

Species: bengalensis

3] Class: Myriapoda: Scolopendra [centipede].

Phylum: Arthropoda - Jointed appendages. Class: Myriapoda - Air breathing,  terrestrial,many pairs of legs. 

Subclass: Opisthogoneta - Genital opening at posterior end of body.

Order: Chilopoda - Many trunk segment, each bearing single pair of leg.

Genus: Scolopendra

Species: Subspinipes.

4] Class: Onychophora: Peripatus [velvet Worm]

Phylum: Arthropoda - Triploblastic, metamerically segmented body.

Class: Onychophora - No external segmentation, appendages not jointed but fleshy.

Subclass: Udeonychophora - Terrestrial animals with ventral mouth.

Order: Euonychophora - Feet possess a pair of claws and a pad 

Family: Peripatidae - Commonly known as velvet worm.

Genus: Peripatus

Species: Capensis.

5]Class: Insecta: Periplaneta [cockroach].

Phylum: Arthropoda-  Jointed appendages, metamerically segmented body.

Class: Insecta - Body divisible into head, thorax & abdomen, six legs. 

Subclass: Pterygota - Wings usually present, abdomen devoid of appendages. 

Order: Dicotyoptera - forewing leathery & hind wing is  membranous. 

Family: Blattidae - Ootheca divided into two rows of Packets.

Genus: Periplaneta

Species: americana.

6]Class: Insecta: Pediculus [ Human louse].

Phylum: Arthropoda - Jointed appendages, metamerically segmented body. 

Class: Insecta - Body divisible into head, thorax. abdomen, six legs.

Subclass :- pterygota - Wings present, metamorphosis is simple.

Order :- Anoplura - Body Flattened, elongated with out wings. legs with single claw for grasping hairs..

Family: Pediculidae - Commonly called human louse.

Genus: Pediculus

Species: humanus.