1. Pereopod 5 not longer than P6 or P7........................................................................... 2
Pereopod 5 much longer than P6 or P7........................................................................ 5
2. Maxilliped without row of setae on distal margin of basal plate (arctic and subarctic of Atlantic)............................................................................. T. abyssorum (Boeck, 1871)
Maxilliped with row of setae on distal margin of basal plate..................................... 3
3. Pereopods 5 & 6; dactylus smooth. Antenna 1 of female hooked, stout (colder waters of Australia and New Zealand) T. australis (Stebbing, 1888)
Pereopods 5 & 6; dactylus with setae at base. Antennae 1 of female straight, tapering (North Pacific)............................................................................................................. 4
4. Antennae 2 of females longer than A1. Adult females reach 9–17 mm in length. Pereopod 3 with 6–8 (usually 7) robust setae on posterior margin of carpus...................... .......................................................................................... T. japonica (Bovallius, 1887)
Antennae 2 of females equal in length to A1. Adult females reach 5–9 mm in length. Pereopod 3 with 3–5 (usually 4) robust setae on posterior margin of carpus................ ........................................................................................... T. pacifica (Stebbing, 1888)
5. Pereopod 7 usually longer than P6, but shorter than P5. Gnathopod 2; merus with relatively straight distal margin,anterodistal corner produced into small tooth(North Atlantic) ................................................................................................. T. compressa Goës, 1865
Pereopod 6 & 7 subequal in length. Gnathopod 2; merus with rounded distal margin 6
6. Pereopods 3–7; dactylus with setae on basal part (arctic and subarctic)........................ ....................................................................... T. libellula (Lichtenstein in Mandt, 1822)
Pereopods 3–7; dactylus smooth (colder waters of southern oceans)............................. ......................................................................................... T. gaudichaudii Guérin, 1825