Unexpectedly, the motionless river clam turned out to be a big liar who could fish!

What's in the GIF below? A small fish swimming around?

No! It's a mussel!

A fish swimming in place? | Youtube: @Laura Hughes

Look from another angle——

No, this is a beautiful clam, Lampsilis cardium, pretending to be a fish | Youtube: @Laura Hughes

Most of our impressions of river clams are that they are delicacies on the table or shells that produce pearls. These guys who live in caves with two heavy shells on their backs look very "lying flat" and can hardly move. But in fact, they have become famous deceivers in freshwater with their excellent cosplay skills.

Eat me? No, raise my baby!

River clams pretend to be fish in order to catch fish.

In the above GIF, the mussels pretending to be fish are species of the genus Lampsilis, which is an expert in fishing among mussels. During the breeding season, female Lampsilis will extend their soft mantle outside the shell and shake it constantly, pretending to be a wounded fish; coupled with the fake eyes near the water inlet and outlet, the effect is very realistic, enough to induce fish to actively attack them.

There are realistic fake eyes at the water inlet and outlet｜Youtube: @Mt Air Wild

But river clams do not "sacrifice" themselves voluntarily. They try to attract fish so that they can help them raise their children.

After the female river clam is fertilized, the fertilized eggs gradually develop into glochid larvae. Most river clams need to feed on the blood or body fluids of fish to live a parasitic life when they are glochid larvae. The glochid larvae hatch from the gills of the female adult clams. They also have two shells with hooks on them to help them hang on to the fish.

The larvae of river mussels｜MC Barnhart 1998

After a period of development, the larvae will fall off the body of the host fish, become a juvenile clam, begin to filter the algae in the water independently, and become an independent clam.

Finding a suitable boarding kindergarten for children is not an easy task. Generally speaking, the larvae of the hookworm need to parasitize fish within 24 hours after formation, and some species can persist for up to 48 hours. River mussels also have high requirements for their parasitic objects. Many river mussels have their own dedicated host fish. If they parasitize the wrong fish, the larvae of the hookworm will be killed by the immunoglobulins of different types of fish.

In order to find a host to rely on, clams have to use a variety of "fishing" techniques.

To fish, everyone shows off their skills

The reason why species of the genus are "fishing experts" is that they can not only impersonate a variety of small fish in the river, but also shrimp and worms. Moreover, the same species of beautiful clams can take on different mimicry forms - in other words, they will use different lures when fishing for different fish.

The green-lined beautiful clam Lampsilis fasciola has many different mimicry｜David T. Zanatta

Polymorphism of mimicry in the green-lined beautiful clam Lampsilis fasciola (Rafinesque, 1820) | Guo Liang

The beautiful clam will trick fish into attacking the fish it pretends to be, especially the fake eyes. The moment the fish bites the bait, the beautiful clam will immediately spray out its offspring, the glochid larvae into the fish's mouth. These little guys, the glochid larvae, are also not ambiguous. They will immediately grab the fish's gills with their shell hooks and quickly complete the parasitism.

The beautiful clam Lampsilis reeveiana (Lea, 1852) attracts Ambloplites constellatus | Guo Liang

Cyprogenia species also fish, but it's the larvae, not the mother clams, that are responsible for the deception.

When the larvae mature, the female clams secrete a large amount of mucus to wrap the larvae inside, forming a larval sac, which is gradually expelled from the shell and fixed with a transparent mucus thread. The larval sac looks like a small fish, drifting with the water, waiting to be swallowed by hungry fish.

A female clam of the genus Pleurotus eryngii extends its larval capsule out of its shell. | Nathan L. Eckert

Cyprogenia is like fishing | Guo Liang

Mussels of the genus Ptychobranchus also make larval capsules, but their method is simpler and more crude. They do not even use the mucus threads that act as fishing lines, but directly expel larval capsules that look like tadpoles or aquatic insect larvae. Once a fish ingests it, the larvae can successfully parasitize it.

The larval capsule of the Ptychobranchus subtentum mimics the larvae of shrimps or aquatic insects, attracting fish such as Cyprinella and Lepomis to eat them. | Guo Liang

The unlucky host will be crushed to death.

The clams mentioned above only allow their larvae to parasitize fish; but some clams may crush their hosts to death when parasitizing, such as the Epioblasma clams that live in the Mississippi River basin in the United States.

Northern spur mussel clamping its host fish | Chris Barnhart / youtube

The proximal clams are one of the most unique clams in terms of reproduction. They have significant sexual dimorphism, which is a rare phenomenon among all river clams in the world.

The shells of female procyonid clams are specialized, and the rear edge of the shell often has sharp teeth. During the breeding season, female procyonid clams will also attract host fish to come and prey on them. At the moment the host is hooked, the clam shell quickly clamps the fish head and forcibly sprays the hook larvae onto the fish's body - and some unlucky hosts will be crushed to death by the sharp teeth on the edge of their shells.

A, Specialized teeth in the shell of female E. capsaeformis used to grab host fish; B, Host fish caught by the head; C, E. brevidens has "bait" shaped like fish eggs on its mantle; D, Northern E. capsaeformis (Lea, 1834) opens its bivalve to lure host fish | Miles Christopher Barnhart et al. / Journal of the North American Benthological Society (2008)

Hitchhiking on a turtle

The clams were still not satisfied with being able to hitchhike on fish, so they set their sights on turtles.

Many painted turtles (Chrysemys picta) live in rivers in New England, USA. Researchers found that some painted turtles were basking in the sun with clumsy steps, as if their legs were injured. A closer look surprised the researchers - a flat oval clam was caught in the turtle's claw!

A clam caught in a turtle's claw | Michael T. Jones et al. / Canadian Field Naturalist (2020)

The flat oval mussel (Elliptio complanata) is a common river mussel found in the United States. As research progresses, it is found that the flat oval mussel not only hangs on the feet of painted turtles, but also follows many other turtles around.

When these freshwater turtles crawl on the riverbed to find food, their claws accidentally slide across the riverbed, and the flat oval clams take this opportunity to clamp their claws and take a "turtle ride." Although turtles are not agile animals, they are still much stronger than clams. Due to many factors such as dams in local rivers, most clams have become extinct or disappeared, and flat oval clams may have spread to other safe water bodies in this wonderful way, making them the most common and widely distributed clams in the eastern United States.

Although we are more accustomed to such clams, they are big deceivers in their natural environment. | Xepheid / Wikimedia Commons

Author: Guo Liang

Editor: pee pee shrimp, maimai

This article comes from the Species Calendar, welcome to forward

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