Unlike some earlier insects, megasecopterans bore two pairs of wings, which were nearly of the same size.

The wings probably were held horizontally, as in dragonflies (Odonata, Anisoptera).

The wing bases tend to be very slender and petiolated, as in damselflies (Odonata, Zygoptera).

The body was usually long and thin, although the genus Protohymen was rather stouter and shorter than a typical megasecopteran.

Another distinctive feature was the presence of a number of fine processes projecting from the body, which in some cases could be longer than the body itself, forming long fringes on the insect's underside.