Answer:
The similarity between a mantle and appendage is that a appendage is a subordinate or subsidiary part or organ; an external organ or limb, esp. of the articulates, however the mantle is a loose garment to be worn over other garments; an enveloping robe; a cloak. Hence, figuratively, a covering or concealing envelope.
Step-by-step explanation:
Mantle - To spread out and to gather or assume.
Appendage - Outgrowth and external body part that
projects from the body.