pontoonshaped

Pontoon-shaped is an adjective used to describe objects or organisms that have two broad, rounded extremities connected by a narrower central region, producing a silhouette reminiscent of a pontoon boat. The form is bilobed and often symmetrical along a central axis.

In geometry and design, pontoon-shaped figures describe a plan or cross-section with two bulges and a constricted waist. In biology, botany, and paleontology, the term is used descriptively for leaves, seeds, shells, carapaces, or other structures that exhibit two rounded lobes separated by a slender neck. The descriptor emphasizes the double-lobed contour rather than overall compactness.

Etymology: the word derives from pontoon, a flotation device, with the suffix -shaped indicating a form. The term is often used alongside dumbbell-shaped or double-lobed to convey a similar double-ended silhouette.

Related concepts include dumbbell-shaped and double-lobed forms, which describe similar two-lobed silhouettes though they may differ in emphasis on ends, neck, or overall convexity.