In the Early Cambrian and Paleozoic eras the predominant animal organism on Earth was the trilobite (www.nytimes.com/2014/03/04/science/when-trilobites-ruled-the-world.html). For 270 million years they were ubiquitous in the oceans until they died out during the Ordovician mass extinction event about 250 million years ago.

There were many thousand of species and paleontologists still study them today. At a digsite sedimentary levels are being excavated by a paleontologist trying to match the various species found with the changing conditions at various times in prehistory.

As the dig progresses salininty analysis of the sediments reveals that the body of water in the region was at various times connected to the ocean (saltwater), partially connected to the ocean (brackish water-possibly an estuary or river) or a fresh ater body (a lake). The paleontologist becomes rather excited as they nd several species previously unknown to science in the freshwater sediments. This very exciting as previously no trilobites had ever been found in freshwater environments.

The further that the dig progresses the more speciation is found according to the salinity level of the site over time. The following information is distilled into various sets of possible trilobites

A: Trilobite species found during periods of freshwater at the site. B: Trilobite species found during periods of saltwater at the site.

C: Heavily armoured trilobite species (with armour plating or spines to prevent predation)

Curiously the paleontologist nds some species present in sediment layers of both saltwater and freshwater eras. These species were usually unarmoured and lived in shallower water. Few armoured species were found in the fresh water eras. They were mainly found during periods of saltwater or brackish water (partial saline environment).

The paleontologist wants to assess relative frequency of armoured saltwater species and the unarmoured species that could tolerate both saltwater and freshwater environments.

(i) Draw a Venn diagram representing the sets A; B and C as per the information presented to you.

(ii)Identify in the Venn diagram the two sets that represent armoured saltwater species and unarmoured species that could tolerate both saltwater and freshwater environ- ments.