“Absorbent intrusion”. Organisms with many marine limbs do not actually push themselves to swim

Polychaete worm – Tomopteris, with movements of metachron waves on each side of the body. Credit: Sean Cole

When you think of swimming, you are probably imagining going through the water, creating a backward push that pushes you forward. New research from the Biological Laboratory (MBL) suggests that many marine animals instead draw in water, which is called “absorption impulse”.

The study was published Scientific reports, found that many small marine animals, including caterpillars, crayfish, and large species of jellyfish, do not push themselves when moving their attachments, but instead release the negative pressure that pulls them through the water.

When the front attachment moves, a low-pressure pocket is created behind it, which can reduce the energy required by the other limb. “It’s like cyclists using conscription to reduce wind և to pull the group,” said Sean Colin, lead author at Roger Williams University, MBL University of Whitman Center.


This publication is based on previous team work, which was also carried out at MBL, through the absorption of lamps and jellyfish. For the current study, they focused on small marine animals that use metachronch kinematics, also known as “metachronous swimming”, a transfer technique commonly used by animals with many pairs of legs in which the appendages strike sequentially rather than simultaneously.

“We went into this study looking for the benefits of post-chronological swimming, but found that the flow around the limbs was very similar to that of a jellyfish or a fish,” said Colin. “Not only is the flow the same, but the negative pressure is the same.”

For this study, researchers worked with two types of shrimp, four types of polysaccharide և comb jellies. All are less than a few millimeters long. They found that the fluid flow created during swimming was the same as that of the larger animals they had previously studied.

Ctenophore Pleurobrachia:

Ctenophore Pleurobrachia trunks (along the left side of the body) at different stages of their electric shock. Credit: Sean Cole

“Even on this really small scale, these animals rely on negative pressure to push themselves through the water,” said Colin, who added that this could be a common occurrence among animals.

“It’s not unique to the fish or jellyfish we see. It is probably much more common in wildlife, ”says Colin, who adds that something like sucking impulses has been observed in birds and bats that move through the air. The limbs of these creatures have the same degree of flexion (25-30 degrees) as the observed marine animals.

Colin and his colleagues are moving forward to study the greater diversity of marine organisms to determine the range of animals that rely on their absorption to push into the water.

Colin says. “This is one of our main goals – to grow, to shrink, to do better research on what animals really rely on for absorption.”

Reference. Sean P. Colin, H. on H. Costello, Kelly R. Sutherland, Brad G. Emel, Onon O. Dabiri և Kevin T. Du Clos’s “The Role of Absorption in the Invertebrate Shovels of Invertebrates”, October 20, 2020 Scientific reports,
DOI: 10.1038 / s41598-020-74745-y:

Colin’s study at the MBL Whitman Center includes Coston Costellon Providence College and John O. Dabiri of the California Institute of Technology. A previous study of lamp beams was conducted in collaboration with MBL senior scientist Enn Enifer Morgan.

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