Ctenophore are characterised by

Options

A. segmentation
B. polymorphism
C. cnidoblasts
D. bioluminescence

Answer

To answer the question "Ctenophores are characterized by," we will go through the characteristics of Ctenophores step by step.

### Step-by-Step Solution:

1. **Definition of Ctenophores**:
- Ctenophores, commonly known as comb jellies or sea walnuts, are a group of marine invertebrates belonging to the phylum Ctenophora.

**Hint**: Remember that Ctenophores are often referred to as "comb jellies" due to their unique locomotion method.

2. **Radial Symmetry**:
- One of the primary characteristics of Ctenophores is that they exhibit radial symmetry. This means their body can be divided into similar halves around a central axis.

**Hint**: Think of how a pizza can be cut into equal slices from the center; this is similar to radial symmetry.

3. **Diploblastic Organization**:
- Ctenophores are diploblastic, which means they have two primary germ layers: the ectoderm and the endoderm. They lack a mesoderm.

**Hint**: "Di" in diploblastic indicates two layers; focus on the two layers of tissues.

4. **Comb Plates**:
- Ctenophores possess unique structures called comb plates or ctenes. These are rows of cilia that help in locomotion, allowing them to move through the water.

**Hint**: Visualize the cilia as tiny hair-like structures that help the jelly move, similar to how a paddle helps a boat.

5. **Bioluminescence**:
- A significant characteristic of Ctenophores is their ability to exhibit bioluminescence, which is the emission of light. This occurs due to a chemical reaction involving molecules called luciferin and an enzyme called luciferase.

**Hint**: Think of bioluminescence as a natural glow; many marine organisms, including Ctenophores, can light up in the dark.

6. **Absence of Segmentation and Polymorphism**:
- Ctenophores do not exhibit segmentation (division into segments) or polymorphism (different forms). These characteristics are not applicable to them.

**Hint**: Segmentation is like the body of an earthworm, while polymorphism refers to different forms in a species, which Ctenophores do not have.

### Conclusion:
The primary characteristic that defines Ctenophores is **bioluminescence**. This is the correct answer to the question, as it highlights their unique ability to emit light.