Stygiiulus, Vagalinski & Borissov & Bobeva & Canciani & Antić, 2022

Vagalinski, Boyan, Borissov, Simeon, Bobeva, Aneliya, Canciani, Giacomo & Antić, Dragan Ž., 2022, The mostly cavernicolous millipede genus Stygiiulus Verhoeff, 1929, stat. nov.: taxonomy, distribution and phylogenetic relationships (Diplopoda, Julida, Julidae), European Journal of Taxonomy 798, pp. 30-69 : 57-58

Key to species of Stygiiulus stat. nov. based on gonopodal and external somatic characters

1. Mouthparts modified for a hydrophilous lifestyle ......................................................................... 2

– Mouthparts normal ....................................................................................................................... 4

2. Opisthomere completely devoid of a posterior hump and with an anteriorly arched, apically finely fringed velum; both the anterior and the posterior branch of solenomere vestgial ......................... ............................................................................................ S. ausugi (Manfredi, 1953) comb. nov.

– Opisthomere with a distinct posterior hump and a rather narrow, marginally deeply serrated velum; solenomere with a well-developed, slender posterior branch ......................................................... 3

3. Promere with the apex turned frontad; velum with serrations on both anterior and posterior margins ................................................................................................................................................ ................................................................................ S. fimbriatus (Strasser, 1971) comb. et stat. nov.

– Promere distally somewhat bent caudad; velum with serrations only on anterior margin ................. ................................................................................. S. gentianae (Strasser, 1971) comb. et stat. nov.

4. Opisthomere completely devoid of a posterior hump ....................................................................... 5

– Opisthomere with a posterior hump ................................................................................................. 6

5. Opisthomere with slender, pointed velum, considerably outreaching solenomere; ozopores set at considerable distance behind pro-metazonal suture ............ S. seewaldi ( Strasser, 1967) comb. nov.

– Opisthomere with a rather broad velum being subequal to solenomere; ozopores set just next to, or on, pro-metazonal suture ..................................................... S. insularis ( Strasser, 1938) comb. nov.

6. Mesomere bent strongly frontad; velum clearly outreaching solenomere; anterior branch of solenomere vestigial, completely fused to velum ................ S. illyricus ( Verhoeff, 1929) comb. nov.

– Mesomere more or less straight; velum shorter than, or subequal to, solenomere; anterior branch of solenomere clearly discernible ......................................................................................................... 7

7. Velum bipartite, the larger anterior part with mostly smooth margins, the posterior one serrated or ciliate; solenomere apically with a rather robust anterior branch and one or two finer posterior branches .................................................................................... S. tobias (Berlese, 1886) comb. nov.

– Velum unipartite, marginally deeply serrated; anterior and posterior branch of solenomere of similar proportions ........................................................................................................................................ 8

8. Promere straight, considerably outreaching mesomere; large species (adults 50–70 cm long) ......... ............................................................................................ S. maximus ( Verhoeff, 1929) comb. nov.

– Promere bent caudad, slightly shorter than mesomere; smaller species (adults 16–35 mm long) ... 9

9. Distal part of mesomere clavate, with a broad and flat apex .............................................................. ...................................................................................... S. montellensis ( Verhoeff, 1930) comb. nov.

– Distal part of mesomere fronto-caudally compressed, with a narrow, rounded apex ......................... ............................................................................... S. rotundatus ( Strasser, 1962) comb. et stat. nov.