Scapheremaeus, Berlese, 1910

Palacios-Vargas, José G., Jaimes Murillo, Kevin A. & Ojeda, Margarita, 2024, New species of Scapheremaeus (Acari: Oribatida: Cymbaeremaeidae) from an epiphytic environment in Morelos, Mexico, Zootaxa 5556 (1), pp. 97-105 : 103-104

Key for all known species of Scapheremaeus from Mexico (modified from Palacios-Vargas et al. 2022)

1. Notogaster without a centrodorsal region; total body length more than two times its width; notogaster rectangular, with a transverse line separating the lenticule... Scapheremaeus alvarezius Ríos and Palacios-Vargas, 1998 (Veracruz: Los Tuxtlas).

- Notogaster with a well-defined centrodorsal region; sensillum (ss) variously shaped................................ 2

2. Notogaster pyriform, almost round, with only seven pairs of setae and strongly contrasting microsculpture between the centrodorsal region and the circumgastric scissure, tridactylous, genitoanal chaetotaxy 4-1-1-2.............................................................. Scapheremaeus colloffi Palacios-Vargas et al. 2022 (Veracruz: Los Tuxtlas).

- Notogaster usually elongate with eight or more pairs of setae, genitoanal chaetotaxy distinct......................... 3

3. Eight pairs of notogastral setae, genitoanal chaetotaxy 6-1-2-3; humeral process very long, pointed and strongly curved............................ Scapheremaeus palaciosi Ríos, 1996 (CDMX: Contreras; Edo. de Mex.: Popocatépetl volcano).

- Notogaster with nine or more pairs of setae................................................................ 4

4. Notogaster with nine pairs of setae, genitoanal chaetotaxy 6-1-2-2, round lenticule.................................................................... Scapheremaeus dirzoius Palacios-Vargas and Páez, 2018 (Veracruz: Los Tuxtlas).

- Notogaster with ten to 13 pairs of setae, distinct genito-anal chaetotaxy.......................................... 5

5. Notogaster irregular with 14 pairs of setae, bidactylous, humeral process pointed........................................ Scapheremaeus baloghius Ríos and Palacios-Vargas, 1998 (Jalisco: Chamela; Chiapas: Chajul; Veracruz: Los Tuxtlas).

- Notogaster with ten pairs of setae........................................................................ 6

6. Epimeral chaetotaxy 3-1-3-3, bidactylous, triangular humeral process present; three pairs of setae in the centrodorsal region........................................ Scapheremaeus schatzi Ríos and Palacios-Vargas, 1998 (Jalisco, Chamela).

- Epimeral chaetotaxy 3-1-2-2............................................................................ 7

7. Notogaster with a well-developed diagonal extensions of centrodorsal region; setae of the centrodorsal region spiniform, c2, la, hi-3 and p1-p3 bacilliform shape; sensillum (Bothridial seta) with a striate capitulum........................................................................................ Scapheremaeus subiasi sp. nov. (El Zapote, Morelos).

- Notogaster without diagonal extensions; total body length less than two times its width............................. 8

8. Centrodorsal region of notogaster with a longitudinal ridge.................................................... 9

- Centrodorsal region of notogaster without a longitudinal ridge................................................ 11

9. Notogaster setae rod-shape with normal alveoli............................................................ 10

- Notogaster setae flame-shaped with relatively large alveoli, lichen-shaped sensillum (Bothridial seta), three longitudinal carinae.... Scapheremaeus flamiferus Palacios-Vargas and Ríos, 1998 ( Nicaragua: León; Mex: Q. Roo, Guerrero, Veracruz) .

10. Sensillum (Bothridial seta) black, barbed and elongated, an incomplete crest between the lenticule and the centrodorsal plate.................. Scapheremaeus grahamius Ríos and Palacios-Vargas, 1998 (CDMX: Reserva Pedregal de San Ángel).

- Sensillum (Bothridial seta) moruliform and elliptical. A lateral and posterior crest to the lenticule that borders the central area present. Posterior margin of the notogaster truncated and a well-developed concavity........................................................... Scapheremaeus tillandsiophilus Ríos and Palacios-Vargas, 1998 (Morelos: Chichinautzin).

11. Centrodorsal region of notogaster with two lateral ridges joining the lm and lp setae; anterior region of notogaster semi rectangular. Rostral setae minute (3 μm).................................................................................................. Scapheremaeus eugenius Ríos y Palacios-Vargas, 1998 (Jalisco: Sierra de Manantlán).

- No lateral ridges and average rostral setae about 10 μm or more............................................... 12

12. Notogaster with ridges between lenticule and central zone................................................... 16

- Notogaster without ridges between the lenticule and the central zone........................................... 13

13. Centrodorsal region of the notogaster almost circular. Prodorsum with very long lamellae, inhabitant rock surfaces........................................................ Scapheremaeus chaac Ríos and Palacios-Vargas, 1998 (Yucatán).

- Centrodorsal region of notogaster elliptic. Prodorsum without lamellae.......................................... 14

14. All setae of notogaster and ad1 and ad2 fungiform, humeral processes spiniform...................................................................... Scapheremaeus fungisetosus Ríos and Palacios-Vargas, 1998 (Jalisco: Chamela).

- Centrodorsal region of the notogaster with or without longitudinal crest, setae no fungiform......................... 15

15. Humeral processes absent. Lamellar setae setiform, lichen-shaped sensillum (Bothridial seta), with a small notch near seta c2 .................................. Scapheremaeus mahunkaius Ríos and Palacios-Vargas, 1998 (Jalisco, Chamela).

- Humeral process present. Lamellar setae bacilliform, sensillum (bothridial seta) head black; no notch near setae c2 .......................................... Scapheremaeus simplex Ríos and Palacios-Vargas, 1998 (Morelos: Chichinautzin).

16. Body very flattened (body length/thickness = 3.4). Lamellar and notogastral setae minute (4μm)........................................................... Scapheremaeus nogueraius Ríos and Palacios-Vargas, 1998 (Jalisco: Chamela).

- Body normal, not flattened (length/thickness = 1.6–2.3). Lamellar setae medium to long........................... 17

17. Sensillum (Bothridial seta) lichen-shaped. Notogaster broad (length/width ratio = 1.5), capitulum sensilla hyaline................................ Scapheremaeus volcanicus Ríos and Palacios-Vargas, 1998 (Edo. de Mex.: volcán Popocatépetl)

- Sensillum (Bothridial seta) has a different shape. Notogaster not as wide........................................ 18

18 Sensilum (Bothridial seta) with a morula-like appearance, body relatively elongated (length/width = 1.8). Humeral process absent......................... Scapheremaeus morulisensillatus Ríos and Palacios-Vargas, 1998 (CDMX: Contreras)

- Sensilla not morula-shaped............................................................................. 19

19 Notogastral setae rod-shaped, long (15 μm).Posterior margin of notogaster with irregular edges. Posterior margin of circumdorsal region strongly projected and triangular........................................................ Scapheremaeus magdalenae Ríos and Palacios-Vargas, 1998 (Baja California: Cedros Island, Baja California Sur: Sierra La Laguna ) .

- Body setae not rod-shaped, distinct, shorter. Posterior margin of notogaster rounded............................... 20

20 Prodorsum with short lamellar cusps, translamella incomplete. Cerotegument strongly developed. Notogaster with two circular central areas. Posterior notogastral setae fungiform............................................................ Scapheremaeus tonatiuh Palacios-Vargas, Rìos and Vázquez, 1998 (Jalisco: Chamela, Q. Roo: Sian Ka’an; Chiapas: Chajul) .

- Prodorsum without lamellar cusps and without translamella. Cerotegument inconspicuous. Notogaster with a single central area, with tiny setae slightly clavate and large alveolus..................................................................................... Scapheremaeus hectorperezius Ríos and Palacios-Vargas, 1998 (Veracruz, Los Tuxtlas).