Option 1 states that the animal had jointed legs. Insects are known for their jointed legs, which allow for movement and agility. This characteristic is unique to insects and not found in earthworms. Earthworms, on the other hand, do not have jointed legs but move using their setae, or bristle-like structures, along their body.

Option 2 states that the body of the animal had very little segmentation. While this is true for earthworms, insects have distinct segmentation in their bodies.

Option 3 states that the body of the animal was cylindrical. This characteristic is common to both insects and earthworms, so it cannot confirm if the animal is an insect or an earthworm.

Option 4 states that the body of the animal was bilaterally symmetrical. This characteristic is also common to both insects and earthworms, so it cannot be used to determine if the animal is an insect or an earthworm.

In conclusion, option 1, the presence of jointed legs, confirms that the animal observed is an insect.