Body slender. Prosome composed of cephalothorax and 3 pedigerous somites. Urosome 4-segmented, with midventral gonopores on genital somite. Rostrum consists of a broad short frontal plate, which is fused to the cephalothorax and ends in 2 acute points on each lateral side. Labrum massive, distal part subdivided into 3 lobes covered with long setules. Caudal rami as long as the urosome, each ramus carries 6 setae.
A1 3-segmented and extends to the genital somite, the 1st segment is as long as the next 2 combined.
A2 biramous. Coxa unarmed, basis with 1 inner setae. Endopodite 2-segmented, longer than exopodite; exopodite 8-segmented.
Md biramous, masticatory blade of gnathobase carries 8 teeth, with 1 lateral tooth large and separate from the others. Basis with 3 inner setae. Endopodite 1-segmented, armed with 6 setae; exopodite 4-segmented, with 2, 1, 1, and 2 setae.
Praecoal arthrite with spines on Mx1. Both endopodite and exopodite 1-segmented, armed with 9 and 7 setae, respectively.
Mx2 5-segmented, 1st segmente elongate, with 4 endites.
Mxp 3- or 4-segmented.
P1-P4 biramous. Coxa and basis unarmed. Inner margin of coxa, basis and proximal endopodal segments of P1 ornamented with stout spinutles or slender setales. Exopodal segments of P1 with strout distolateral spine-like outgrowth.
P5 absent, or represented by 2 pairs of setae on ventral midline.
Mormonilla Giesbrecht, 1891