Hansen, 1911
Generic diagnosis:
The eyes are large, higher than broad, and transversely constricted.
The frontal plate is short, broad, and triangular, and the edges are sharply upturned (T. oculatum dorsal head). There is no rostral process.
The 2nd and 3rd thoracic legs are extremely elongate, and the 2 terminal segments have spine-like bristles along both edges (Tessarabrachion-thoracic legs). Legs 1 and 4-6 are normally developed. The endopod of leg 7 is lacking in males, but in females it has 1 or 2 segments. The endopod of leg 8 is lacking and the exopod is a rudimentary segment, as in Thysanoessa.
The basal segment of the peduncle of the 1st antenna lacks a lappet and is very much broader than the next two segments which are broader in the male than in the female. In the male the upper flagellum is shorter than the compressed-appearing lower one.
The petasma of the male carries only two or three fine marginal spines on the inner lobe, which is not separated from the median lobe. The setiferous lobe and the auxiliary lobe are both well developed.
The genus is monospecific.