Only the right mandible is functional in the insect order:

Correct option is A

Collembola (commonly known as springtails) are primitive, wingless hexapods that are closely related to insects, though not true insects under modern classifications. They are primarily found in soil, leaf litter, and other moist habitats and play a vital role in decomposing organic matter.
�� Mouthparts in Collembola:
· Collembolans have entognathous mouthparts, meaning their mouthparts are enclosed within folds of the head capsule.
· Their mandibles are asymmetrical.
· Notably, only the right mandible is functional while the left mandible is either vestigial or absent.
· This feature is distinctive and unique to Collembola, aiding in scraping or chewing fungal hyphae, decaying plant matter, and microorganisms.
Explanation for Each Option
(a) Collembola ✅
· Correct answer.
· In Collembola, only the right mandible is functional, and this asymmetry is a key anatomical trait used in classification.
(b) Protura ❌
· Protura are also entognathous and primitive, but they lack traditional mandibles altogether and feed via piercing and sucking mouthparts.
· Hence, the concept of "functional right mandible" doesn’t apply.
(c) Coleoptera ❌
· Beetles have well-developed, symmetrical mandibles, used for chewing.
· Both mandibles are fully functional.
(d) Orthoptera ❌
· Grasshoppers and crickets possess powerful, symmetrical mandibles for cutting and grinding plant material.
· Both sides are fully operational.