1. Introduction
2. Data
2.1. Galaxy And Mass Assembly
2.2. XXL
2.3. Comparison with existing X-ray clusters
3. X-ray over luminous and under luminous group selection
3.1. Metric for selection
3.2. X-ray over luminosity sub-samples
3.3. Sub-sample comparisons
4. Results
4.1. Group structural parameters
4.2. Galaxy properties
5. Discussion
5.1. X-ray luminosity as a measure of group age
5.2. Group structural parameters in larger systems
5.3. Evolved X-ray under luminous groups
5.4. X-ray versus optical selection
5.5. The role of large-scale structure
5.6. Potential biases
6. Summary