1 Precloacal supplements present in males...................................................................2
- Precloacal supplements absent in males.................................................................... 9
2 Body longer than 1.5 mm............................................................................... 3
- Body shorter than 1.3 mm............................................................................... 4
3 Cephalic setae much shorter (1/6–1/5 hd long), 21–28 precloacal supplements.......................... H. antarcticus
- Cephalic setae 1hd long, 9 precloacal supplements................................................. H. setosoides
4 Pharynx without distinct terminal bulb.................................................................... 5
- Pharynx with distinct terminal bulb.......................................................................6
5 Cephalic setae 2 hd long......................................................................... H. setosus
- Cephalic setae short than 1 hd long............................................................... H. abyssalis
6 19–24 precloacal supplements................................................................... H. balticus
- Precloacal supplements less than 15.......................................................................7
7 Cuticle with lateral differentiation of 2 longitudinal rows of dots, 8 precloacal supplements................. H. marleenae
- At least female cuticle with lateral differentiation of 4 longitudinal rows of dots.................................... 8
8 Male with 2, female with 4 lateral longitudinal rows of dots, gubernaculum with anterior-lateral apophysis, 7 precloacal sup- plements.................................................................................. H. dimorphus
- Both male and female with 4 lateral longitudinal rows of dots, gubernaculum without anterior-lateral apophysis, 11–15 preclo- acal supplements............................................................................ H. inaequalis
9 Cephalic setae longer than 1 h.d. long.................................................................... 10
- Cephalic setae shorter than 1 h.d......................................................................... 15
10 Labial sensilla setose, pharyngeal bulb present.............................................................11
- Labial sensilla papillose, pharyngeal bulb absent....................................................... H. colesi
11 Gubernaculum with apophysis..........................................................................12
- Gubernaculum without apophysis........................................................................ 13
12 Body length longer than 500µm, apophysis of gubernaculum hooked..................................... H. steineri
- Body length shorter than 500µm, apophysis of gubernaculum not hooked............................ H. galapagensis
13 Gubernaculum well developed, spoon-shaped, halfe the length of the spicula.................. H. schuurmansstekhoveni
- Gubernaculum reduced to a short plate, much shorter than half the length of the spicula............................. 14
14 Spicula nearly equal width throughout, distal blunt, 17 µm long........................................ H. solivagus
- Spicula tapering unevenly, distal pointed, 21µm long............................................... H. interruptus
15 Cephalic setae 2/3 h.d long............................................................................. 16
- Cephalic setae shorter than 0.5 h.d........................................................................ 19
16 Gubernaculum with apophysis.......................................................................... 17
- Gubernaculum without apophysis........................................................................18
17 Body longer than 610 µm, gubernaculum with ventral apophysis........................... H. ventrapophyses sp. nov.
- Body shorter than 470 µm, gubernaculum with dorsal apophysis........................................ H. pumilio
18 Gubernaculum distally with two teeth.............................................................. H. pilosus
- Gubernaculum distally without any tooth.......................................................... H. longiseta
19 Pharyngeal base slightly dilated, no bulb..................................................... H. obtusicaudatus
- Pharyngeal bulb well developed......................................................................... 20
20 Gubernaculum with strong dorsal apophysis................................................... H. mediterraneus
- Gubernaculum without any apophysis.................................................................... 21
21 Body longer than 900 µm, cephalic setae 6 µm, somatic setae 7–8 µm.................................... H. angelae
- Body shorter than 800µm, cephalic setae absent, somatic setae up to 30 µm............................... H. reverus