It might be taking it too far calling us two peas in a pod. The more I learn, however, the more alike we seem. Maybe this is an inter-species example of twins separated at birth.

My long-lost twin is a marine mollusk called a chiton.
Though we don’t necessarily look alike, we do share some interesting attributes. Start with size. Chitons are the “minis” of the marine mollusk family. Atlantic coast chitons seldom exceed one inch and, similarly, even on a good day I don’t reach five feet tall. Other members of the chiton family are larger and can exceed one foot in length. My siblings also grew to exceed their small sister.
Chitons are tough on the outside and soft on the inside. With their armor-like shell that attaches to rocks or other hard surfaces, only a few persistent predators are able to make a meal of them. Besides humans, only birds, sea stars, crabs and lobsters can break their strong seal. In deference to their protective shell, they are also called “coat of mail” shells.
Unlike bivalves with their two shells, or gastropods with a single one, chitons have their own unique covering consisting of eight plates or valves that overlap and are encircled by a mantle and girdle which holds those plates together. When dislodged from its solid substrate, this animal will curl up in a ball like a pill bug. After the animal dies, the plates separate and can wash up on the beach. When found singly, the plates are called butterfly shells, due to their resemblance to those fluttery wings.
With a chiton’s calciferous covering, you could say that all of those butterfly shells are carbon copies. Aragonite is what the shell plates are made of, which is a crystal form of calcium carbonate, making them hard to handle.
Living and working at the same place provides me with a very small home range. The same is true of the chiton which spends its entire life in an area of water of only a few feet. While it is generally a sessile creature, if the chiton is moved from its home, it will exhibit homing behavior and return to its original spot.
 There are areas where we differ. Chitons are vegetarians, eating algae and micro-nutrients using their radula or rasping tongue, while I have been known occasionally to eat meat. Chitons also lack a true brain and have a three-chambered heart, unlike us humans that are possessed of a large brain and four-chambered heart. Chitons also pre-date humans, having fossil records that go back more than 400 million years.
Though some differences do exist, I prefer to find commonality with my underwater neighbor. Mollusk or not, it seems that I have met my match.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.