Whatever Catches My Fancy

Paul Klee

Above: Fastosarion brazieri, commonly known as the chameleon semi-slug, and an unidentified species of semi-slug from the genus Sheldonia

The term "semi-slug" is used to describe an intermediate stage of evolution that occurs as snails evolve into slugs. Nearly 1,000 different species of semi-slug are currently known to exist, and these bizarre little creatures can be found on at least four continents.

Above: Fastosarion brazieri and Varadia amboliensis

Each species of semi-slug is technically still classified as a snail, but its shell is noticeably reduced, becoming smaller and more internalized as the species evolves. A semi-slug officially becomes a regular-slug once its shell is no longer visible at all.

As this article explains:

If life were simple, there would be snails and slugs. Snails carry their homes on their backs; slugs are naked and embarrassed. But life isn’t simple, so of course there’s secret option #3 – the semi-slug, a bizarre creature that sits exactly between the snail and the slug.

Above: genus Satiella and genus Euaustenia

This article describes the distinction between a snail, a slug, and a semi-slug:

In contrast to snails, which have an external shell large enough to accommodate the body, or slugs, in which the shell is completely internal or absent, semi-slugs have an external shell, but the shell is too small to accommodate the animal’s entire body.

Above: Megaustenia siamensis

The evolutionary process that causes the shell to recede is known as limacization, and it's especially common in moist, low-calcium environments where a snail's shell may be more of a burden than a benefit:

Terrestrial slugs are not a monophyletic group, but a case of convergent evolution in which the slug form evolved from different lineages of land snails that gradually lost their shell through a process called limacization. Limacization resulted in adaptive radiation in land snail lineages, as slugs became adapted to diverse moist and protected spaces, such as crevices in rocks and wood debris. The loss of the shell also allowed for more movement and less calcium dependence, making slugs more successful as pests.

Above: Gaeotis nigrolineata, also known as the Puerto Rican semi-slug, has a neon green shell that is almost completely internalized, but the shell is clearly visible through the semi-slug's translucent body

Some semi-slugs have shells that are still opaque and largely visible, with a patch of flesh covering only the outer edges of the shell, while others have shells that are more significantly reduced, transparent, and/or concealed.

Above: Ibycus rachelae, commonly known as the green-shelled semi-slug, and a species of semi-slug from the genus Durgella

This topic was mentioned in my previous post about Ibycus rachelae, but I wanted to write a more detailed post about semi-slugs, because they're just so fascinating and weird.

Above: a black-and-white semi-slug from subfamily Sheldoniinae

Above: Fastosarion brazieri again, but this one is especially spiky for some reason

Sources & More Info:

Australian Geographic: Meet the Semi-Slug, a Snail without a Home

Carnegie Museum of Natural History: What's So Good about Being a Slug?

Frontiers: Terrestrial Slugs in Neotropical Agroecosystems (PDF)

iNaturalist: Photos 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, & 12

The Shell-Makers: Introducing Molluscs: On Becoming Sluggish

Land Snails and Slugs of Sabah and Labuan, Malaysia: Semi-Slugs

slate roof tiles

John Gaius tells us (well, Harrow) in Nona the Ninth that he always hated change, but even in Harrow the Ninth it’s clear—he and his lyctors are stagnating and have been for millennia. They’re constantly talking about how great things used to be (sexy parties, Cassiopeia’s cooking, etc.). They have no hope for the future. John has a spaceship full of bodies in cryosleep—literally frozen in time and undying but also unable to grow or live. He is the Emperor Undying.

The theme becomes more explicit in Nona the Ninth: we see John (and arguably BOE) stuck on this 10,000-year-old grudge and unable to move past it. He thought he could keep Alecto in stasis in a tomb what, forever? He makes Gideon into a non-living preserved version of herself.

Meanwhile the characters who are living and growing are changing, even when it’s sometimes awful, because it’s how they keep doing what needs to be done. Palamedes and Camilla say before they become Paul that it wasn’t inevitable, but it is the best thing they can do now: they will make this imperfect irreversible change because that’s how they keep living and protecting the people they love. On the trip to the Ninth, Nona considers it might be better to just die, instead of continue this uncertain journey forward, but ultimately accepts irrevocable, painful change because NOODLE. And because “You can’t take loved away”: change doesn’t destroy the past or invalidate the good that existed there. Living requires change, but change doesn’t require forgetting.

these are images from a 1930s pamphlet that endorsed kudzu, entitled "stop gullies: save your farm"