Taxonomic key to the genus Adropion and species of Diphascon lacking a DABT

Remark: Adropion gani requires further investigation (see above) in order to ascribe it to the correct genus (i.e. a new genus or Pilatobius). Therefore, it is excluded from the key, together with A. marcusi sp. dub. Note that although D. greveni and D. mauccii Dastych & McInnes, 1996 belong within Diphasconinae (Tumanov and Tsvetkova 2023), they cannot be distinguished morphologically from Adropion based on the currently recognized taxonomic criteria and are thus included in the key.

1. Macroplacoids granular ............................................................................................................................................................................... 2

– Macroplacoids bar-shaped .......................................................................................................................................................................... 4

2. Internal bars I–III present ......................................................................................................................................... Adropion gordonense

– Internal bars I–III absent ............................................................................................................................................................................. 3

3. Macroplacoid length sequence 1 <2 <3, dorsal granulation absent ............................................................... Adropion linzhiensis

– Macroplacoid length sequence 2 <1 <3, dorsal granulation present .......................................................... Adropion afroglacialis

4. Three macroplacoids present ...................................................................................................................................................................... 5

– Two macroplacoids present ........................................................................................................................................................................ 9

5. Both microplacoid and septulum present ................................................................................................................................................ 6

– Only microplacoid or septulum present .................................................................................................................................................. 7

6. Bases of external claws I-III with indented bases, pt of SSIP = 67–75% ............................................................. Diphascon greveni

– Bases of external claws I-III with smooth bases, pt of SSIP = 64–65% ................................................................... Adropion onorei

7. Microplacoid absent, septulum present .................................................................................................................... Diphascon mauccii

– Microplacoid present, septulum absent ................................................................................................................................................... 8

8. Eyes present ................................................................................................................................. Adropion ommatophorum comb. nov.

– Eyes absent ....................................................................................................................................................................... Adropion scoticum

9. Cuticular bars absent (the edges of external pulvini I–III may be faintly visible) .............................................. Adropion belgicae

– Median and internal cuticular bars I–III and posterior bars between bases of claw IV present ...................................................... .................................................................................................................................... Adropion diphasconiellum comb. nov. et stat. rev.