Raillietina tetragona is the largest among avian tapeworms, measuring up to 30 cm in length and 1–1.5 cm in breadth. It is whitish in colour, highly elongated, dorso-ventrally flattened, and entirely covered with a tegument. The body is divisible into the head region called 'scolex', followed by an unsegmented 'neck', and then by highly segmented body proper called strobila. The strobila is composed of a series of ribbon-like body segments called proglottids, gradually enlarging from the anterior end towards the posterior. The scolex bears an apical rounded rostellum, which is armed with 100 minute hooks, arranged in single row. This is surrounded by four suckers which are lined with 5-6 rows of spines. The most important diagnostic characters in comparison to other species are oval scolex and suckers, with relatively elongated neck.
