1. Ep3 with posteromedian and posteroventral tooth (posterior border forming an angular protrusion) ( Fig. 12A)............................................................................................................................................. 2
– Ep3 with posteroventral tooth only (posterior border rounded) ( Fig. 7C)........................................... 4
2. Pereionite 7 with 0-1 posterodorsal tooth; pleonite 1 and 2 with 1 posterodorsal tooth ..................... 3
– Pereionite 7 and pleonites 1-2 with 3 posterodorsal teeth ............................... H. nilssoni Ohlin, 1895
3. Telson distally truncated and slightly concave; ventral border of coxae 1-2 smooth; posterior border of basis of P5-7 with very weak crenulations; carpus of Gn1-2 equal to propodus.............................................................................................. H. fulvocinctus (M. Sars, 1859)
– Telson pointed, with large distal tooth flanked by 2 pairs of small lateral subdistal teeth; ventral border of coxae 1-2 and posterior border of basis of P5-7 distinctly serrate; carpus of Gn1-2 distinctly longer than propodus........................................................................................................ H. stappersi sp. nov.
4. Ventral lobe of head produced into a sharp tooth; carpus of Gn1-2 about 4 x as long as broad or narrower; at least some segments of pleon with posterodorsal tooth*; telson pointed; bathyal and abyssal species ..................................................................................................................................... 5
– Ventral lobe of head bluntly subquadrate; carpus of Gn1-2 a bit less than 2 x as long as broad; pleon smooth, segments without posterodorsal tooth; telson truncated; infralittoral species....................................................................................................... H. mixtus Stephensen, 1931
5. Eyes present ......................................................................................................................................... 6
– Eyes absent........................................................................................................................................... 7
6. Eye large and broad; coxa 1 with anteroventral corner pointing anteriorly; ventral border of coxa 1 with about 20 pronounced serrations; posteroventral corner of basis of P7 forming a sharp square angle; pereionite 7 (and often 6) and pleonites 1-2 with posterodorsal tooth; tip of telson tridentate ........................................................................................ H. qvadridentatus G.O. Sars, 1877
– Eye small and subreniform; coxa 1 with anteroventral corner forming a square angle; ventral border of coxa 1 with about 10 weak crenulations; posteroventral corner of basis of P7 bluntly angular; pereionite 7 (but never 6) and pleonites 1-2 with posterodorsal tooth; tip of telson with a single distal tooth .......................................................................................................................... H. cainae sp. nov.
7. Ventral border of coxa 1-2 with pronounced serrations........................ H. gorbunovi Gurjanova, 1946
– Ventral border of coxa 1-2 smooth or nearly so...................................... H. caecus Kamenskaya, 1980
* The pleon of the type specimens of H. gorbunovi (and only known specimens) is missing and its ornamentation is therefore unknown. However, since that species looks very similar to H. qvadridentatus, it is assumed that some of the posterior body segments have a posterodorsal tooth.