Brachionus falcatus has an occipital margin with six spines. The intermediate spines are notably longer and curved ventrally, while the median and lateral spines are shorter and of nearly equal length. The posterior spines are long, incurved, and have widely separated bases. However, the anterior and posterior spines can vary considerably. In a specific form of this species found in large numbers in a river, the spines are notably shorter. This modification with shorter spines may be an adaptation for existence in running water, as longer spines are prone to entangling easily. The lorica of Brachionus falcatus is composed of both a dorsal and ventral plate, and it is compressed dorso-ventrally. The anterior dorsal margin of the lorica features six spines, with the intermediates being much longer than the laterals and curved laterally outwards. The median spines are approximately equal in length to the lateral spines.