Ibycus Rachelae - Blog Posts

Green Shell Semi-Slug: the researchers who discovered this species originally wanted to name it "Ibycus felis," because it often rests with its tail curled around its body, which reminded them of a sleeping cat

The Latin name of this species is Ibycus rachelae, but it's also known as a green-shelled or long-tailed semi-slug. The species was first described in 2008, and it is found only in the montane forests of Sabah (Borneo) and Peninsular Malaysia.

The term "semi-slug" refers to an intermediate stage of evolution as a snail evolves into a slug. These snails still have shells that are at least partially visible, but they have been reduced to the point where the shell can no longer accommodate the snail's whole body. There are many different species of semi-slug, but most of them have a noticeably reduced, receding, and/or transparent shell that is partially concealed beneath the mantle.

This article describes another peculiar characteristic of semi-slugs (including Ibycus rachelae):

... semi-slugs don’t just look weird, they act weird, too. They employ sharp projectiles called love darts in their courtship rituals, by shooting several of them at a prospective mate. The mate, in turn, shoots several love darts right back.

Researchers have found that if semi-slugs are able to lodge love darts into one another, the subsequent copulation tends to be much more successful. It’s thought that the mucus distributed by the love dart ensures greater survivability of the sperm

This is what the "love darts" look like (when magnified under SEM):

The tiny, harpoon-like structures are made of calcium carbonate, and they transmit certain hormones (via mucus) that help to increase the likelihood of reproductive success. Semi-slugs are not the only gastropods that use "love darts," however; they are also used by some other land snails and slugs.

Sources & More Info:

World Wildlife Fund: Borneo's New World (PDF)

Basteria (Journal): The Slugs and Semislugs of Sabah, Malaysian Borneo (PDF)

Forest Research Institute Malaysia: Introduction to the Land Snails and Slugs of Malaysia (PDF)

Malay Peninsular Terrestrial Molluscs: Ibycus rachelae

Live Science: World's Longest Bug and 'Ninja' Slug Discovered in Borneo

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