Leiobunum rotundum is chestnut-brown, with a small, smooth, and very long round or oval body and thin black legs,[1] as well as having no separation between the head and the abdomen.

Numerous large nephrocytes occur in clusters between the muscles in the anterior region of the body.

[2] As at 2023 this species is regarded as newly introduced to British Columbia in Canada and Washington in the United States.

[5] The species can be found among vegetation such as long grass, herbaceous plants, shrubs, and trees.

Small invertebrates that it eats include caterpillars, mites, woodlice, and slugs.