A tiny swimming barrelSourced
Those barrel-like hoops are an animal’s muscles
Doliolids are small marine animals with barrel-shaped bodies, openings at both ends and circular muscle bands. They filter food particles from passing water. Contracting their muscle bands produces a jet that can propel them forward or backward.
The apparent barrel hoops are part of the propulsion system.
Summary / translation: Unbubly · CC BY-SA 4.0
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Doliolida · Wikimedia contributors
Adapted, summarized and translated from the source. Adapted text is also available under CC BY-SA 4.0.
Reviewed: 2026-10-10