Question

In which of the following animal post-anal tail is found?
a. Earthworm
b. Lower invertebrate
c. Scorpion
d. Snake

Answer 1

A post-anal tail is a characteristic feature of all the chordates. It is a body extension running alongside an anal opening. In certain species, provide the aquatic organisms with a means of locomotion.

Complete answer:

Option A is incorrect. An earthworm is a terrestrial invertebrate that occurs worldwide where the Opisthopora order includes soil, water, and temperature. They exhibit a tube-within-a-tube body plan, are segmented externally with corresponding internal segmentation, and typically have setae on all segments and do not have a post-anal tail.

Option B is incorrect. Though tails are mainly a characteristic of vertebrates, lower invertebrates have tail-like appendages which are often referred to as tails, like scorpions and springtails, as well as snails and slugs.

Option C is incorrect. The short segmented "tail" or metasome, often born over the back in a distinctive forward curve, finishing with a poisonous stinger. It consists of five segments, not just one segment, and the telon.

Option D is correct. The spinal cord is a post-anal tail that extends beyond the anus of the animal present in the posterior region of the body. It contains skeletal elements and muscles which provide a source of locomotive movement for aquatic species. Postanal tails are a characteristic of all chordates and the snake would therefore possess the post-anal tail out of four choices.
So, the correct answer is Option D.

Note: The post-anal tail is a subsequent elongation of the body which extends beyond the anus. The tail also helps with balance, courting, and signaling in some terrestrial vertebrates when nearby danger. The post-anal tail is present during embryonic development in humans and other primates but it is vestigial as an adult.