Anterior mouth, gills in operculum,2-chambered heart.

Explanation

To identify the organisms with the features of an anterior mouth, gills in operculum, and a 2-chambered heart, we can follow these steps:

### Step 1: Understand the Features
- **Anterior Mouth**: This indicates that the mouth is located at the front of the organism.
- **Gills in Operculum**: This means that the gills are protected by a bony flap known as the operculum.
- **2-Chambered Heart**: This refers to a heart structure that consists of two chambers, typically one atrium and one ventricle.

### Step 2: Classify the Organisms
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