Hiyamugi noodles are cut noodles that have a shape different from the udon noodles, and because they are also discussed in conjunction with somen noodles, it can be assumed that they are cut noodles whose shape is close to that of somen noodles.
それとは形状の異なる切り麺であり、素麺と並べて論じられているので、形状は素麺に近い細い切り麺と推測される。