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A Natural History Lexicon | Mantle

Welcome to Wingtrip’s Natural History Lexicon, a regular rundown of natural history terms, however varied and at random. To find future and past posts on this subject, simply search “natural history lexicon” or find it in the tags. Thanks for reading!

Mantle
Noun

/ˈman(t)l/

– A loose, sleeveless cloak or cape.
– Something that covers, envelops, or conceals: the mantle of darkness.
– Geology: the portion of the earth, about 1800 miles (2900km) thick, between the crust and the core.
-Zoology: A single or paired outgrowth of the body wall that lines the inner surface of  the valves of the shell in mollusks and brachiopods.
-Ornithology: the back, scapular, and inner wing plumage, especially when of the same color and distinct from other plumage.

On the occasional Monday I’m on farm egg duty and I stroll up through the little forest road to grab several cartons for the self-service egg stand. On this short walk I see many things, from early spring Calypso Orchids, freshly fledged Dark-eyed Juncos, and the vacuous deer who stare while grinding their choice greenery.

When I am on egg duty, it means no other hominids are around and despite avoiding my misanthropic tendencies, I enjoy this time. On this week’s journey we’d had some well deserved rain; everything felt fresh. I paused to watch a Hairy Woodpecker investigating the rotten stubs of broken branches and as I did, something on the ground caught my eye.

Looking down I discovered a pretty snail, spreading itself happily across a bit of fluorescent green lichen. What caught my eye was not actually the shell, which blended well with the earth tones of the forest floor, but the mantle, which was a beautiful bumpy coral red.

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A good demonstration of what a land snail’s mantle is used for.

The term mantle is a catch all that’s been used in variety of ways in the world of natural history, but stems from its roots, which revolve around concealment and capes. While a noun, it can be a verb, as raptorial birds may be found mantling over their prey. In both birds and mollusks (slugs, snails, clams, octopus, squid, etc.), the anatomical region defined as such typically extends out neatly below the head, very much looking the part of a cape in form and function.

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A Banana Slug (Ariolimax columbianus ) on the farm.

I found a Banana Slug enjoying the moisture on one of our outbuildings moments later and got to appreciate how the mantle we see in these gastropods really acts as a modified foot. Shells on gastropods emanate from the mantle. The cavity created by its folding may hold anatomy related to feeding, breathing, waste disposal, and even acting as brooding chamber. The mantle is a central part of their biology, but mostly what we see are the margins of a slug or snail’s mantle sliding about the environment.

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A closer look at the Pacific Sideband (Monadenia fidelis).

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Lewis’s moon snail’s (Neverita lewisii) mantle extending around its shell.

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The bizarre Pinto Abalone’s (Haliotis kamtschatkana) mantle (Abalone are a type of marine snail).

As soon as you start noticing something you tend to notice more, and the idea of mantles in the animal world stuck with me on my walk. A Violet-Green Swallow sitting near its nest had a beautiful iridescent green mantle, formed of feathers of the wing and wing coverts. This cape of feathers overlaps in the direction of the tail, shedding wind and water. In the birding and ornithological world, the mantle is often more talked about when it’s of contrast with the rest of the coloration but obviously all birds have such structure. Gulls are an excellent example, but infrequently would a crow’s mantle be discussed.

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A Western Gull (Larus occidentalis) and its dark gray mantle.

 

 

 

 

 

 

 

 

 

I passed the lovely snail several more times during the day, as it made its slow way toward a destination only it knew. As things warmed I found it against a Douglas Fir, fully tucked into its shell, for safe keeping and to avoid moisture loss. Even the mantles itself needs to be hidden in the case of snails.

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