Sam and Paul had found a colony of green algae or chlorophyceae.
Step-by-step explanation:
The eukaryotic unicellular organisms are classified under the kingdom of Protista. This kingdom, along with the algae, also constitutes the other organisms like protozoans, smile moulds etc.
The green algae are pre plants in nature, with most of the characteristics of a bryophyte. They do have a cell wall made of cellulose. And also, they have flagella in their normal cells. They are unicellular in nature, but often are colonial. They do have chloroplasts which makes them look green, and also makes them photosynthetic and hence, autotrophic. They are both marine as well as fresh water living. These organisms do undergo both sexual and asexual modes of reproduction.