How does a snail make its shells

Tanks with additional benefits: snails let their shells loose on worms

Snails are among the most successful animals in the world. They have existed for a very long time and live in many forms almost everywhere. One reason for the success story is the animals' unique blueprint, which includes the snail shell as a particularly noticeable feature. This is not only used as an armor against enemies or as a support structure for the intestines of the molluscs, as Robbie Rae from Liverpool John Moores University found out by chance: Even ordinary garden snails actively use their shell as an immune weapon against hostile nematodes, reports Rae in Scientific Reports magazine.

The researcher - actually a geneticist - investigated the question of why many shell snails are almost completely resistant to roundworms, whereas other snails are devastating. In fact, worms like kill Phasmarhabditis hermaphrodita some mollusks are so effective that they are being advertised in specialist horticultural shops for the biological control of nudibranch pests such as the small flail.

Rae now tested first in the laboratory by finding roundworms on tapered snails (Cepeae nemoralis) started. This species is known to be resistant to the worms - many other snails, especially slugs, die quickly after the nematodes have invaded the mollusc and released bacteria. After two weeks of unrelenting worm attacks in the laboratory that appeared to have no consequences, the researcher dissected the previously healthy test snails and looked for the whereabouts of the worms. He found what he was looking for on the inside of the shell: here, hundreds of worms were often fixed in lime capsules and rendered harmless, which the shell-producing cells of the snails had apparently deposited.

Rae now went to look for C. nemoralis-Snails from the wild and collected a variety of animals living in the wild, which also had nematode capsules in large numbers. He also discovered the same phenomenon in a good 1,300 shells of 43 species of land snail, which he borrowed from museum collections. In fact, even the remains of the shell, which are no longer visible from the outside and which remain under the skin of many nudibranchs, still seem to have retained their immune function, says Rae: After attempts at infection, he discovered encapsulated worm parasites on the reduced shield of slugs and other nudibranch species.

Obviously, the worm defense by shell capsule is a very old, widespread mechanism that could possibly have been applied to the oldest shell-bearing common ancestor of all molluscs 550 million years ago. This once had a rather small shell, which should not have made much use as a tank against large enemies. Perhaps, the researcher speculates, it was already protecting the primeval molluscs from hostile worms - like the roundworms that may have existed as early as the late Cambrian.