Rykellus

Santos, Jandir C., Castilho, Raphael C., Silva, Edmilson S. & De Moraes, Gilberto J., 2015, Two new species of Rykellus (Acari: Mesostigmata: Ologamasidae) from Brazil and a key to the world species of the genus, Zootaxa 3926 (1), pp. 111-121 : 119-120

Key to world species of Rykellus based on adult females

Rykellus is most similar to Hydrogamasellus Hischmann. Species of the latter genus also have podonotal and opisthonotal shields fused, but the line of fusion of Hydrogamasellus species is not distinct.

Four species were mentioned by Karg & Schorlemmer (2013) in Rykellus ( R. brevipellitus , R. darglensis , R. nkandhlaensis and R. ovalis ). Two species previously placed in Hydrogamasellus were recently transferred to Rykellus because they have the typical characteristics of species of this genus, including the distinct, complete and V-shaped line of fusion between podonotal and opisthonotal shields ( Santos et al., 2013). These are R. ubatubaensis and R. longopilus . The former had been placed in Hydrogamasellus for convenience by Lee (1970), but the author considered it a species incertae sedis.

Sufficient information is presently available in the literature to allow the recognition of all species attributed to this genus. These can be separated with the use of the following key.

1. Sternal shield fused with section of endopodal shield near coxae IV; exopodal shields totally fused with peritrematic shield. 2

- Sternal shield not fused with section of endopodal shield near coxae IV; only posterior end of exopodal shield fused with peritrematic shield........................................................................................ 3

2. Seta Z 5 about 1.1 times as long as J 5; ventrianal shield with the two most anterior setae in longitudinal line............................................................................. Rykellus darglensis ( Ryke, 1962) , South Africa

- Seta Z 5 about 8 times as long as J 5; ventrianal shield with the two most anterior setae in transverse line............................................................................. Rykellus nkandhlaensis ( Ryke, 1962) , South Africa

3. Podonotal region of dorsal shield with 19–20 pairs of setae................................................... 4

- Podonotal region of dorsal shield with 22 pairs of setae...................................................... 5

4. Podonotal region of dorsal shield with 19 pairs of setae; opisthogaster with seven pairs of setae (Jv 1– Jv 3, Jv 5 and Zv 1– Zv 3; Jv 4 absent)............................................. Rykellus brevipellitus Karg & Schorlemmer, 2009 , Brazil

- Podonotal region of dorsal shield with 20 pairs of setae; opisthogaster with eight pairs of setae (Jv 1– Jv 5 and Zv 1– Zv 3).............................................................. Rykellus ovalis Karg & Schorlemmer, 2013 , Paraguay

5. Setae J 2, J 3 and J 4 at least as long as distance between their bases and bases of respective subsequent setae of J series..... 6

- Setae J 2, J 3 and J 4 at most half as long as distance between their bases and bases of respective subsequent setae of J series. 7

6. Opisthonotal region of dorsal shield with 21 pairs of setae (J 1– J 5, Z 1– Z 5, S 1– S 5, R 1– R 5 and UR 5); ventrianal shield with six pairs of setae (Zv 3 on unsclerotised integument along margins of the shield)..................................................................................................... Rykellus ubatubaensis ( Hirschmann, 1966) , Brazil

- Opisthonotal region of dorsal shield with 18 pairs of setae (J 1– J 5, Z 1– Z 5, S 1– S 5 and R 2– R 4); ventrianal shield with seven pairs of setae (Zv 3 on the shield).......................................... Rykellus longopilus ( Karg, 1976) , Chile

7. Anterolateral extensions of epistome rounded distally; with a platelet between presternal plates; ventrianal shield with anterolateral reticulation.............................................................. Rykellus anibali n. sp., Brazil

- Anterolateral extensions of epistome sharp-tipped; without platelet between presternal plates; ventrianal shield without anterolateral reticulation............................................................. Rykellus mineiroi n. sp., Brazil