Key to Malagasy Mystrium Species

A key to worker, queen and male Mystrium species in the Malagasy region. Based on: Yoshimura, M. & Fisher, B.L. 2014. A revision of the ant genus Mystrium in the Malagasy region with description of six new species and remarks on Amblyopone and Stigmatomma (Hymenoptera, Formicidae, Amblyoponinae). ZooKeys 394, 1–99. doi:10.3897/zookeys.394.6446

There are two keys: a worker and queen key, followed by a key to the known males.

Key to Workers and Queens

1

 * Wings present and well developed. Wing sclerites fully developed even with wings removed (Fig. 7A). Both anterior and lateral ocelli distinct (Fig. 7C) . . . . . 2


 * Wings absent or vestigial. Wing sclerites undeveloped or incomplete (Fig. 7B). Lateral ocelli absent (Fig. 7D) . . . . . 5

2
return to couplet #1
 * Labrum with distinct longitudinal ridge on its middle portion (Fig. 8A). Distal portion of abdominal sternum VII with single pair of stout spines (Fig. 8C). Body size relatively large (HW>1.9 mm)(mysticum species group, part) . . . . . 3


 * Labrum without distinct longitudinal ridge on its middle portion (Fig. 8B). Distal portion of abdominal sternum VII with two pairs of stout spines (Fig. 8D). Body size relatively small (HW<1.7 mm)(camillae species group, part) . . . . . 4

3
return to couplet #2
 * Setae (=hairs) on dorsal surface of head and pronotum simple (Fig. 9A). Anterior margin of clypeus convex (Fig. 9C) (queen and intercaste) . . . . . Mystrium mysticum


 * Setae (=hairs) on dorsal surface of head and pronotum spatulate (Fig. 9B). Anterior margin of clypeus straight or weakly concave (Fig. 9D) (queen and intercaste) . . . . . Mystrium rogeri

4
return to couplet #2
 * Petiole short in dorsal view, 0.5× length of abdominal segment III (Fig. 10A). Setae on pronotal dorsum narrow and sharp on its apex. First flagellomere (third segment of antenna) distinctly shorter than pedicel (second segment of antenna) (Fig. 10C). Body yellow to yellowish brown (queen) . . . . . Mystrium barrybressleri


 * Petiole long in dorsal view, 0.7× length of abdominal segment III (Fig. 10B). Setae on pronotal dorsum spatulate and dull on its apex. First flagellomere as long as pedicel (Fig. 10D). Body blackish brown (queen) . . . . . Mystrium labyrinth

5
return to couplet #1
 * Ventral half of vertex unsculptured, smooth (Fig. 11A). Labrum with distinct longitudinal ridge on its middle portion (as in Fig. 8A). Distal portion of abdominal sternum VII with single pair of stout spines (Fig. 8D). Anterior ocellus sometimes present (mysticum species group, worker and intercaste) . . . . . 6


 * Ventral half of vertex sculptured (Fig. 11B). Labrum without distinct longitudinal ridge on its middle portion (as in Fig. 8B). Distal portion of abdominal sternum VII with two pairs of stout spines (Fig. 8D). Ocelli absent . . . . . 7

6
return to couplet #5
 * Anterior margin of clypeus convex (as in Fig. 9C). Among same-sized individuals, combination of following characters usually observed: sculpture relatively shallow and weak on lateral surface of pronotum; difference in width of dorsal surface of mandible larger between mandibular shaft (narrowest part) and distal portion (widest part) (Fig. 12A); petiole in dorsal view relatively wider (worker and intercaste) . . . . . Mystrium mysticum


 * Anterior margin of clypeus straight or weakly concave (as in Fig. 9D). Among same sized individuals, combination of following characters usually observed: sculpture relatively deep and strong on lateral surface of pronotum; difference in width of dorsal surface of mandible smaller between mandibular shaft (narrowest part) and distal portion (widest part) (Fig. 12B); petiole in dorsal view relatively narrower (worker and intercaste) . . . . . Mystrium rogeri

7
return to couplet #5
 * Head dorsum and pronotum strongly to weakly and regularly reticulate (Fig. 13A). No deep longitudinal furrow on midline of pronotum. Second maxillary palpomere shorter than third (Fig. 13C) (camillae group, worker) . . . . . 8


 * Head dorsum and pronotum finely to roughly sculptured longitudinally, but not regularly reticulate (Fig. 13B). Pronotum often with deep longitudinal furrow along midline. Second maxillary palpomere longer than third (Fig. 13D) (voeltzkowi group) . . . . . 9

8
return to couplet #7
 * First flagellomere segment of antenna distinctly shorter than pedicel (as in Fig. 10C). Genal tooth relatively short, distinctly failing to reach to anterior margin of lateral lobe of clypeus (Fig. 14A). No carina present on dorsal edge of metapleural gland bulla. Body size relatively small (HW<1.50 mm). Petiole relatively wider in dorsal view (PtI>195). Body yellowish brown to reddish brown (worker) . . . . . Mystrium barrybressleri


 * First flagellomere as long as pedicel (as in Fig 10D). Genal tooth relatively long, almost reaching anterior margin of lateral lobe of clypeus (Fig. 14B). Distinct carina present on dorsal edge of metapleural gland bulla. Body size relatively large (HW>1.70 mm). Petiole relatively narrower in dorsal view (PtI<185). Body reddish brown to black (worker) . . . . . Mystrium labyrinth

9
return to couplet #7
 * Apical tooth strongly sclerotized, its apex darker than basal portion, strongly curving inward (Fig. 15A) (voeltzkowi group, worker) . . . . . 10
 * Apical tooth moderately sclerotized, its apex same color as basal portion, straight and directed ventrally (Fig. 15B) (voeltzkowi group, ergatoid queen)  . . . . . 15

10
return to couplet #9
 * With head in posterior view, posterior face of vertex forming right or even acute angle with its dorsal face on median line, on lateral portion of vertex as steep as median portion (Fig. 16A) . . . . . 11


 * With head in posterior view, posterior face of vertex forming blunt angle with its dorsal face on median line, lateral portion of vertex distinctly steeper than median portion (Fig. 16B) . . . . . 13

11
return to couplet #10
 * Dorsal surface of pronotum without strong, deep, and thick longitudinal striae (Fig. 17A). Genal tooth undeveloped, distinctly fails to reach anterior margin of lateral lobe of clypeus in full-face view (Fig. 17C). Clypeal conical setae extremely small and short (Fig. 17C). Metanotal groove indistinct in lateral view. Mesonotum often not differentiated from propodeum in dorsal view (worker) . . . . . Mystrium janovitzi


 * Dorsal surface of pronotum with strong, deep, and thick longitudinal striae (Fig. 17B). Genal tooth distinctly developed, almost reach to anterior margin of lateral lobe of clypeus in full-face view (Fig. 17D). Clypeal conical setae long (Fig. 17D). Metanotal groove shallow but distinct in lateral view. Mesonotum always clearly differentiated from propodeum in dorsal view . . . . . 12

12
return to couplet #11
 * Anterior margin of clypeus straight (Fig. 18A). First flagellomere longer than pedicel (Fig. 18C). With mandible in dorsal view, width of visible surface on distal portion almost the same as on mandibular shaft (Fig. 18E) (worker) . . . . . Mystrium oberthueri


 * Anterior margin of clypeus strongly convex (Fig. 18B). First flagellomere as long as pedicel (Fig. 18D). With mandible in dorsal view, visible surface on distal portion slightly wider than on mandibular shaft (Fig. 18F) (worker) . . . . . Mystrium eques

13
return to couplet #10
 * Anterior margin of clypeus strongly convex with long conical setae, of which median pair usually larger than adjacent pair (Fig. 19A) (worker) . . . . . Mystrium shadow


 * Anterior margin of clypeus almost straight, with short conical setae, of which median pair usually smaller than adjacent pair (Fig. 19B) . . . . . 14

14
return to couplet #13
 * Genal tooth relatively short, reaching or slightly exceeding basal line of lateral clypeal lobe (Fig. 20A). Eye relatively larger than in individuals of Mystrium voeltzkowi of same body size (Fig. 20C). Metapleural gland bulla weakly developed, posterior margin of propodeal declivity almost straight (Fig. 20E) (worker) . . . . . Mystrium mirror


 * Genal tooth relatively long, reaching to about half of lateral clypeal lobe (Fig. 20B). Eye relatively smaller than Mystrium mirror in individuals of same body size (Fig. 20D). Metapleural gland bulla strongly developed, posterior margin of propodeal declivity distinctly convex posteriorly on its ventral side (Fig. 20F) (worker) . . . . . Mystrium voeltzkowi

15
return to couplet #9
 * With head in posterior view, posterior face of vertex forming right or even acute angle with its dorsal face on median line, lateral portion of vertex as steep as on median portion (Fig. 21A) . . . . . 16


 * With head in posterior view, posterior face of vertex forming blunt angle with its dorsal face on median line, lateral portion of vertex distinctly steeper than median portion (Fig. 21B) . . . . . 18

16
return to couplet #15
 * Anterior margin of clypeus strongly convex (Fig. 22A) (ergatoid queen) . . . . . Mystrium eques


 * Anterior margin of clypeus almost straight (Fig. 22B) . . . . . 17

17
return to couplet #16
 * Clypeal conical setae extremely short (Fig. 23A). First flagellomere as long as pedicel (Fig. 23C) (ergatoid queen) . . . . . Mystrium janovitzi


 * Clypeal conical setae moderately long (Fig. 23B). First flagellomere longer than pedicel (Fig. 23D) (ergatoid queen) . . . . . Mystrium oberthueri

18
return to couplet #15
 * Metapleural gland bulla extremely well developed, expanding above propodeal spiracle (Fig. 24A). Propodeal declivity in lateral view strongly convex posteriorly on its ventral two thirds (ergatoid queen) . . . . . Mystrium voeltzkowi


 * Metapleural gland bulla weakly to moderately developed, not expanding above propodeal spiracle (Fig. 24B). Propodeal declivity in lateral view usually straight or convex posteriorly on its ventral third . . . . . 19

19
return to couplet #18
 * Setae on pronotal dorsum almost simple, narrowing distally, with sharp apex (Fig. 25A). Anterolateral corner of head usually without spine, but sometimes with small spine. Vestigial wings often unclear and unrecognizable, or existing as quite small appendage (Fig. 25C) (ergatoid queen) . . . . . Mystrium mirror


 * Setae on pronotal dorsum spatulate, widened distally and with sharp apex (Fig. 25B). Anterolateral corner of head with small spine. Vestigial wings clearly recognizable as appendages (Fig. 25D) (ergatoid queen) . . . . . Mystrium shadow 

Key to Males

Males of Mystrium labyrinth and Mystrium eques are unknown.

1M

 * Lateral ocellus relatively large and close to eye; distance between lateral ocellus and eye less than 1.2× maximum diameter of lateral ocellus (Fig. 26A). Eye large, occupying about 0.75× of head length (Fig. 26C). Body relatively brighter . . . . . 2M


 * Lateral ocellus relatively small and distant from eye; distance between lateral ocellus and eye more than 1.2× maximum diameter of lateral ocellus (Fig. 26B). Eye relatively smaller, occupying 0.5-0.6× of head length (Fig. 26D). Body relatively darker . . . . . 3M

2M
return to couplet #1M
 * Distal portion of aedeagus rounded (Fig. 27A). Basal ring gently extending basally (Fig. 27C) . . . . . Mystrium voeltzkowi


 * Distal portion of aedeagus relatively sharp (Fig. 27B). Basal ring not extending basally (Fig. 27D) . . . . . Mystrium mirror

3M
return to couplet #1M
 * Abdominal tergum VIII punctured (Fig. 28A). Petiolar dorsum covered with rough, deep punctures (Fig. 28C). Eye relatively small, occupying about half of head . . . . . 4M


 * Abdominal tergum VIII smooth and not punctured (Fig. 28B). Petiolar dorsum smooth, or covered with fine punctures, or at most shallow, irregular punctures (Fig. 28D). Eye relatively large, occupying about 0.6× of head length . . . . . 5M

4M
return to couplet #3M
 * Basoventral expansion of aedeagus long, its distal portion relatively narrow and sharp (Fig. 29A) . . . . . Mystrium mysticum


 * Basoventral expansion of aedeagus short, its distal portion relatively wide and rounded (Fig. 29B) . . . . . Mystrium rogeri

5M
return to couplet #3M
 * With head in full-face view, dorsal margin of head straight (Fig. 30A) . . . . . Mystrium oberthueri


 * With head in full-face view, dorsal margin of head somewhat rounded (Fig. 30B) . . . . . 6M

6M
return to couplet #5M
 * Body size smaller (HW<1.20 mm). With head in full-face view, lateral ocelli clearly protruding from dorsal margin of head (Fig. 31A). On forewing, cu-a usually located at junction of Media (M) and Cubitus (Cu), sometimes slightly basal from junction (Fig. 31C). Petiole in dorsal view shorter, its length 0.5× of that of abdominal tergite III . . . . . Mystrium barrybressleri


 * Body size larger (HW>1.50 mm). With head in full-face view, lateral ocelli reaching or failing to reach dorsal margin of head (Fig. 31B). On forewing, cu-a located far basal from junction of Media (M) and Cubitus (Cu) (Fig. 31D). Petiole in dorsal view longer, its length 0.6× or more of that of abdominal tergite III . . . . . 7M

7M
return to couplet #6M
 * Posterior face of vertex gently rising from neck, posterior and dorsal faces almost continuous without division (Fig. 32A). Basoventral expansion of aedeagus relatively short (Fig. 32C) . . . . . Mystrium shadow


 * Posterior face of vertex steeply rising from neck, posterior and dorsal faces clearly divided (Fig. 32B). Basoventral expansion of aedeagus relatively long (Fig. 32D) . . . . . Mystrium janovitzi