Arthropoda: Introduction
| Content Type | Notes |
|---|---|
| Status | In progress |
| Chapter | Biology of Non-Chordates |
| Course | Graduation |
| Reference | From NCERT, uou.ac.in |
| Subject | Zoology |
| Topic | Arthropoda. Introduction / Basics |
| Ruhul Amin | |
| Progress (%) | 100 |
| Difficulty Level | |
| Mistake type | |
| Previous Year Questions |
Arthropoda
- This is the largest phylum of Animalia which includes mainly insects.
- Some of the more well-known arthropods include insects, crustaceans, spiders, scorpion and centipede as well as the fossil trilobites.
- Over two-thirds of all named species on earth are arthropods (Figure 4.12).
- Arthropods are mainly terrestrial but marine and freshwater species are also well known.
- They range in size from microscopic plankton to life-forms that are a few meter long.
- Arthropoda varies tremendously in their habitats, life histories, and dietary preferences.
Body
- They have organ-system level of organisation.
- They are bilaterally symmetrical, triploblastic, segmented and coelomate animals.
- Arthropod bodies are divided into segments.
- However, a number of segments are sometimes fused to form integrated body parts known as tagmata.
- This process of fusion is called tagmosis.
- The head, thorax, and abdomen are examples of tagmata.
- The body consists of head, thorax and abdomen.
- In insects, the anterior portion of the heart is extended into a tube that is called an aorta which directs the blood forward as it goes out into the body cavity.
- The body of arthropods is covered by chitinous exoskeleton.
- Exoskeleton serves as protection and provides places for muscle attachment.
- Arthropods must molt because their exoskeletons don’t grow with them.
- They have jointed appendages (arthros-joint, poda-appendages).
- However, in most species some appendages have been modified to form other structures, such as mouthparts, antennae, or reproductive organs.
- Arthropod appendages may be either biramous (branched) or uniramous (unbranched).
- Respiratory organs are gills, book gills, book lungs or tracheal system.
- The tracheal respiratory system consists of external openings called spiracles that are linked to a system of branched tubules which allow respiratory gases to reach internal tissues.
- Circulatory system is of open type.
- Arthropods primary internal cavity is known as hemocoel, which accommodates their internal organs, and through which their haemolymph - analogue of blood - circulates; they have open circulatory systems.
- Arthropods have a well-developed, mesodermal, solid nerve cord, ventral and well-developed sense organs.
- Arthropods are characterized by a brain as well as a nerve ring around the area of the pharynx, in the oral cavity.
- A double nerve cord extends backwards along the ventral surface of the body, and each body segment is associated with its own ganglion, or mass of nerve cells.
- Sensory organs like antennae, eyes (compound and simple), statocysts or balancing organs are present.
- Excretion takes place through malpighian tubules.
- They are mostly dioecious.
- Fertilisation is usually internal.
- They are mostly oviparous.
- Development may be direct or indirect.
- Examples: Economically important insects – Apis (Honeybee), Bombyx (Silkworm), Laccifer (Lac insect) Vectors – Anopheles, Culex and Aedes (Mosquitoes) Gregarious pest – Locusta (Locust) Living fossil – Limulus (King crab).
