Planes minutus is a small crab, reaching a maximum carapace length of 17.5 millimetres (0.7 in), and typically less than 10 mm (0.4 in).

[2] It differs from the larger P. major in that males have a broadly triangular abdomen, rather than one which narrows abruptly after the third segment, and from P. marinus in having flattened legs with a fringe of setae that aid in swimming.

This is often supplemented with large patches of white, apparently imitating the calcareous tubes attached by annelid worms to Sargassum.

[3] The diet of P. minutus is very varied, including small fish, krill, isopods, sea skaters and squid, and food items may be stored for later consumption.

On September 17, 1492, in the Sargasso Sea near 28°N 37°W / 28°N 37°W / 28; -37, he recorded "much more weed appearing, like herbs from rivers, in which they found a live crab, which the Admiral kept.

[4] Sporadic records followed from different oceans, but the first name to be accepted under the International Code of Zoological Nomenclature is the name "Cancer minutus", published by Carl Linnaeus in his 1758 10th edition of Systema Naturae.