Naryciodes Caterpillars: these caterpillars have tiny, gelatinous bodies that mimic the appearance of a snail; they even have appendages that resemble eyestalks, but they're located on the caterpillar's rump
The scientific name of this species is Naryciodes posticalis, and it can be found only in Japan. It belongs to the Limacodidae family of moths, which are commonly known as slug moths, because their caterpillars often have a gelatinous, slug-like appearance. That name seems a little ironic in this case, because Naryciodes posticalis actually mimics a snail.
Above: Naryciodes posticalis
Each caterpillar has a bulge in the center of its body, with colorful markings that form three concentric layers on its back. Those features mimic the appearance of a snail shell, which might help to deter predators. The caterpillar is also equipped with two short, stubby appendages that resemble eyestalks, but they're actually located at the back of its body.
Above: this photo shows the underside of the caterpillar's body, with its mouth slightly visible on the right
According to this article (translated from Japanese):
Even during the final instar, the caterpillars' body length remains quite small—approximately 8 mm—and because their morphology resembles that of a snail, I believe that they are often overlooked. Since their host plants are abundant along mountain streams and similar areas within the Kanto region, the larvae are most frequently discovered in such environments.
Above: a close-up of the caterpillar's head
Despite my best efforts, I couldn't find any other information about these strange little creatures, and I get the sense that the entire genus is still poorly-studied.
Sources & More Info:
iNaturalist: Naryciodes posticalis
Kawasaki Organization for Nature Research and Conservation: A Record of Naryciodes posticalis in Ikuta Ryokuchi Park (PDF)
Zootaxa: A New Species of Naryciodes from Korea
Keishu's Insect Encyclopedia: Broad-Leaved Moth
