Swimmer (The Vanishing Venusians)

The Swimmers (as they're known by the Flower-people) are an aquatic species of predatory vegetable-creatures from the highlands of Venus, which dwell in rivers and move in large numbers, seeking out prey in the riverbanks.

Biology
The Swimmers are large, plant-based humanoids adapted for an aquatic existence. They have no bones in their bodies; being both light and flexible, and have shimmering membranous wings to aid in swimming.

Despite their size, they can swim with great swiftness and agility. They emit a phosphorescent glow; particularly on their wings. Their blood is described as sticky and greenish. They have spiny needle-sharp claws, full-black lidless eyes, and "flat, coiled growths" on their heads, resembling fungi.

Immature individuals have their heads covered in mobile petal-like sensory organs that make them resemble dandelions instead. These immature individuals also lack proper wings, having only a shimmering membrane instead, and are much more cumbersome than the adults.

Swimmers move around in large groups and, despite being naturally aquatic, are capable of pursuing prey on land with "suckered, spidery legs". While hunting, they sometimes produce loud vocalizations, which might be used for intimidation of prey or coordination of the attack.

Appearances

 * "The Vanishing Venusians", by Leigh Brackett (1945)