Biramous

Biramous is a term used for branched arthropod appendages. These are most commonly branched into a gill and leg with a common root at a body segment. Each leg/gill structure will be paired with a second biramous structure on the other side of the body. Biramous appendages are best known from trilobites where all the legs -- both on the head and the thorax -- are parts of biramous structures with a gill branching off above the leg. The converse of biramous is uniramous or -- very rarely -- monoramous. Uniramous structures are unbranched. Uniramous structures are also found in arthropods. Examples of uniramous structures are trilobite antennae and the legs of chelicerates.