Class arachnida is characterised by

Options

A. A pair each of pedipalpi and chelicerae
B. Four pairs of legs
C. Both A and B
D. Three pairs of legs.

Answer

**Step-by-Step Solution:**

1. **Definition of Class Arachnida**: Class Arachnida is a group of invertebrates that belong to the phylum Arthropoda. This class includes organisms such as spiders, scorpions, ticks, and mites.

2. **Body Structure**: Arachnids are characterized by having two main body segments: the cephalothorax (which is a fusion of the head and thorax) and the abdomen. This is different from insects, which have three body segments (head, thorax, abdomen).

3. **Number of Legs**: One of the defining features of arachnids is that they possess eight legs. This distinguishes them from insects, which have six legs.

4. **Habitat**: Most arachnids are terrestrial, meaning they primarily live on land. They are adapted to various environments, including deserts, forests, and grasslands.

5. **Lack of Antennae**: Unlike insects, arachnids do not have antennae. Instead, they have specialized mouthparts called chelicerae, which are used for feeding.

6. **Respiration**: Arachnids typically breathe through book lungs or tracheae, which are specialized respiratory structures.

7. **Reproduction**: Arachnids generally reproduce sexually, and many species exhibit interesting mating behaviors. They often lay eggs, which can be protected in silk sacs or other structures.

**Final Summary**: Class Arachnida is characterized by having eight legs, two body segments (cephalothorax and abdomen), the absence of antennae, terrestrial habitats, unique respiratory structures, and specific reproductive strategies.

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