Arthropoda - General classification (Theory ) Dr. Vidhin Kamble

     

PHYLUM – ARTHROPODA -GENERAL CHARACTERS

1.      Arthropoda means jointed legs.  It includes individuals with jointed appendages.

2.      It is the largest phylum in the animal kingdom, comprises 80 percent of animal species.

3.       Found in a cosmopolitan area.

4.      They are omnivorous in feeding habit Some forms are carnivorous (Scorpion)

5.      Some organisms are ectoparasite

6.      The digestive system is complete and well developed

7.      They are triploblastic, bilaterally symmetrical.

8.      The body is divisible into head thorax and abdomen.

9.      The exoskeleton is made up of chitinous cuticle and protein.

10.     Presence of a pair of antennae.

11.     Molting or ecdysis is the most common phenomenon, which facilitates growth.

12.     Presence of the true haemo-coelomic cavity filled with hemolymph or   

          haemocoelomic fluid.

13.      Respiratory pigment if present is hemocyanin (few are with hemoglobin).

14.      Respiratory pigment hemocyanin contains copper.

15.     The sensory organs are compound eyes, anal cirri, bristles, statocyst, antenna, etc.

16.     Excretory organs are green glands or coxal glands.  In terrestrial arthropods malphigian  

           tubules.

17.   They are mostly unisexual i. e. Sexes are separate.

18.     Sexual dimorphism is occurs

19.     Internal fertilization occurs in aquatic forms. Internal fertilization occurs in terrestrial

         forms.

20.     Development is direct or indirect.

21.     The egg is centrolecithal.

22.      Cleavage is meroblastic and superficial. 

  

CLASSIFICATION OF ARTHROPODA

Phylum Arthropoda is classified into five classes

1.     CLASS-I: CRUSTACEA

2.     CLASS-II: CHILOPODA

3.     CLASS-III: DIPLOPODA or DIGNATHA

4.     CLASS-IV: INSECTA or HEXAPODA

5.     CLASS –: ARACHNIDA

CLASS-I: CRUSTACEA

1. Crustaceans are -mostly Aquatic marine arthropods. Few are freshwater forms.

2. in most of the species, cephalothorax is present. i.e. head and thorax unite to form Cephalothorax

3. presence of 5 pairs of cephalic appendages.  In includes one pair of first antennae (antennules) one pair of second antennae, one pair of mandibles, one pair of first maxillae and a pair of second maxillae.

4. crustaceans are the only arthropods with two pairs of antennae.

5. In Crustaceae, thoracic and abdominal appendages are  Biramous.

6. Respiratory by gill.

7. Excretory organs are Green glands or Antennal gland

8. Sense organs include compound eyes, antennae, and statocysts,

Ex: Palimony(freshwater prawn) Balanus (rock barnacle) Astacus (crayfish) Cancer(crab) Daphnia(water flea)

CLASS-II: CHILOPODA

1. This class includes centipedes.

2. These are terrestrial and carnivorous.

3. They are trignathic - with mandibles, first maxillae, and second maxillae.

4. The body is divisible into head and trunk only.

5. Each segment of the trunk shows the presence of one pair of clawed legs.

6. The first pair of trunk appendages bear -poison claws.

7. Respiration by tracheae.

8. Excretory organs are Malpighian tubules

9. Presence of single genital aperture at the posterior end of the trunk

10. Development is direct or indirect

E.g. : Scolopendra, Scutigera

CLASS-III: DIPLOPODA or DIGNATHA

1. The animals belong to this class are millipedes. Commonly called as Thousand legged worms.

2.     They are terrestrial forms.

3.   The body is divisible into the head, thorax, and abdomen.

4.  They are dignathic animals with mandibles and gnathochilarium which is formed by the fusion of second maxillae.

5.  They are detritivorous in feeding habit, feeding upon decaying plant material.

6.     The trunk segments are diplosegments formed by the fusion of two-segment during embryonic development.

7.     Each segment consists of two pairs of legs and two pairs of spiracles.

8.     Respiration by trachea.

9.     Excretion takes place by Malpighian tubules.

10.         Development is indirect.

E.g. Spirobolus, Julus

CLASS-IV: INSECTA or HEXAPODA

1.     The individuals in a class Insecta are with three pairs of jointed legs, hence referred to as Hexapoda.

2.     The body is divided into Head, Thorax, and Abdomen.

3.     The respiration through the trachea.

4.     Excretory organs are the Malpighian tubules.

5.     the nitrogenous waste is in the form of uric acid (Uricotelism).

6.     Development is indirect.

7.     Larval stage in early life.

8.     Development by metamorphosis.

E.g. : - Musca (Housefly) Lepisma (Silverfish), Pediculus (Head louse), Periplanata cockroach

CLASS –V: ARACHNIDA

1.     Most of the animals are terrestrial.

2.     The chelicerates animals  belong to-Arachnida

3.     The body is divisible into prosoma, meso-soma, and meta-soma.

4.     The prosoma shows the presence of six pairs of appendages. One pair of chelicerae, one pair of post-oral pedipalp and four pairs of walking legs.

5.     In case of spider chelicera shows the presence of fang containing the poison gland.

6.     Respiratory organs are book lung in the scorpion, in spider respiration through book lung or trachea or by both.

7.     Excretory organs are malphigian tubules and coxal glands.

8.     Development is direct.

9.     Some forms are viviparous (Scorpion)

E.g.: Plamnaeus (Scorpion) Aranea (Spider) Sarcoptes (Mite)