What amazing skills do sea snails, known as “global travelers,” have?

Author: Liu Yi

Source: Knowledge is Power Magazine

In March 2021, the author found a large number of blue-purple sea snails and long sea snails on the beach during an intertidal zone survey in Lingshui, Hainan. They were stranded on the beach after drifting nearby with the ocean current and being swept to the beach by big waves. Why are sea snails known as "global travelers"? In order to successfully complete their travel plans, what survival skills do sea snails have mastered?

Floating equipment - bubble float

Long sea snail and its floating sac and purple egg sac

Sea snails, also known as purple snails, have a one-time piece of equipment to adapt to their life-long floating life on the sea surface: a bubble float composed of hundreds of small air sacs.

The gastropod of sea snails is a magical bubble-making machine. In life, their shells face the sea surface, and the front end of their gastropods is exposed above the water surface. They continuously stretch and retract to take in air. The glands on the gastropods then secrete mucus, which wraps the taken-in air into small air sacs. The mucus hardens when it encounters seawater, and it takes less than a minute to make a small air sac. Usually, sea snails will make dozens of small air sacs in one breath before stopping to rest for a while. These small air sacs will be constantly squeezed and adhered during the manufacturing process, and eventually form a bubble sac with elasticity and sufficient buoyancy. Sea snails can easily float on the sea surface with it. They just need to fix the sac without any additional movement. They are truly masters of "lying flat" once and for all.

During the breeding season, female sea snails produce a large number of purple egg sacs and secrete mucus to stick them to the bottom of the floating sacs one by one, forming a considerable group of egg sacs that float with the mother. Therefore, among the sea snails that are hit by the waves on the beach, you can sometimes see individuals with densely packed egg sacs stuck under the floating sacs.

Sea snail deformation meter

In addition to the bubble bladder, the sea snail also performs a series of "transformations".

A long sea snail with purple egg sacs stranded on the beach, the ventral side of the shell is dark in color

Long sea snail with purple egg sac stranded on the beach, the back of the shell is light in color

First, the shells of sea snails become very brittle and thin, reducing weight as much as possible and making them easier to float;

Secondly, the shell of the sea snail is blue-purple. In the blue ocean, the blue shell color can blend in well with the environment, thus hiding itself. What's more interesting is that the ventral side of the shell near the mouth of the snail is darker in color, while the back of the shell is whiter in color. In this way, whether you look down from the sky or look up from the sea, the sea snail can blend in perfectly with the environment, thus playing the role of "invisibility";

Third, there is no mouth cover (i.e., operculum). The mouth cover has a function similar to a "door". However, sea snails do not need a mouth cover. On the one hand, in order to float, they must always fix the buoyancy bladder, so their heads and part of their ventral feet must be exposed outside the shell, and they cannot "close the door". On the other hand, their fragile shells are vulnerable. Once they encounter predators, even if they have a mouth cover, it will be useless. Therefore, in the process of evolution, sea snails completely "throw away" the mouth cover.

Eat whatever you come across

Sea snails cannot swim and can only rely on their buoyancy bladders to drift with the current, so they can only "sit back and wait", but their food is still divided into staple food and snacks.

A stranded long sea snail preying on a sail jellyfish

A sea snail is eating a young fish. Most of the young fish's body has been rolled into the esophagus by its two radulas, leaving only the fish's head with wide eyes and a small section of its tail exposed.

The main food of sea snails is silver coin jellyfish, sail jellyfish and Portuguese man-of-war, because these jellyfish are also blue creatures that always float on the sea surface and drift with the waves. There are huge numbers of them, so the probability of being encountered and preyed by sea snails is the highest. In addition, some small creatures will randomly appear on the surrounding sea surface, and they will not refuse these snacks, such as floating insects, floating myoga, and even sea snails. Occasionally, they will kill each other.

Sea snail with float bladder, secreting purple dye

In addition to the powerful radula "meat grinder", sea snails also have a secret weapon - when necessary during the hunting process, they will secrete a purple dye with a paralyzing effect, causing the prey to surrender obediently.

In addition to being used as an anesthetic when hunting, the sea snail's purple dye may also be released when it encounters danger, thereby acting as a defense.

Over millions of years, sea snails have evolved special skills to adapt to the life of "drifting in the sea". They seem to drift with the ocean currents without a destination, but due to their large numbers, they sometimes gather into a conspicuous white "foam line" in the ocean, and sometimes they are hit by big waves and thrown onto the beach, ending their drifting journey.

Sea snails act as a link that connects the ocean, intertidal zones and land, allowing matter and energy to flow.

(Editor-in-charge: Wang Jiaying; Art editor: Zhou You)