Archaebacteria is a domain of unicellular micro organisms, which constitute a group of most primitive forms of prokaryotes ( that is devoid of nucleus and membrane bound subcellular organelles). The organism under this domain are adapted to survive under extremely harsh conditions ( therefore also called extremophiles) such as boiling mud around volcano, hotsprings.
Example- Methanogens.
In the question, scientists were able to collect the organisms by using microscope slides, which were dipped into the boiling hot springs.
Thus, it represents the organisms collected were Archaebacteria.
