Define sexual dimorphism. Give an example of an invertebrate phylum which shows this feature.

Explanation

### Step-by-Step Solution:

1. **Define Sexual Dimorphism**:
- Sexual dimorphism refers to the differences in physical characteristics between males and females of the same species. These differences can include size, color, shape, and other morphological features. In essence, male and female individuals exhibit distinct physical appearances that allow for their differentiation.

2. **Provide an Example of an Invertebrate Phylum**:
- An example of an invertebrate phylum that exhibits sexual dimorphism is the phylum Annelida. In this phylum, male and female organisms often show noticeable differences in their physical characteristics.