Question

Which of the following is not a trend seen in the evolution of animals?

• A. Ancestral forms with two openings in digestive tract $\to$ derived forms with one opening in digestive tract.
• B. Ancestral forms with open circulatory system $\to$ derived forms with dosed circulatory system
• C. Ancestral forms with one or two embryonic germ layers $\to$ derived forms with three distinct germ layers
• D. Ancestral forms with radial symmetry $\to$ derived forms with bilateral symmetry

Answer 1

The correct option is A Ancestral forms with two openings in digestive tract $\to$ derived forms with one opening in digestive tract.

Digestive tract in primitive animals have a single gut opening (gastrovascular cavity) that acts both as mouth to ingest food and anus to expel out the waste in early animals. This is seen in Platyhelminthes, Cnideria etc. This evolved into the alimentary canal with two openings: a mouth for ingesting food, and anus for eliminating waste as seen in nematodes and higher animals.

So, the correct option is 'Ancestral forms with two openings in digestive tract → derived forms with one opening in the digestive tract.'