Key to selected species of Cardiocondyla

This key to selected species of Cardiocondyla is based on Seifert (2022).

The key below considering the Orientalic and Australasian faunal regions would have to encompass not only the 26 species of the seven species groups treated by Seifert (2022) but also 15 species from other species groups occurring here. Several of the latter are world-wide tramp species of African origin. For reasons given in the introduction, I will not consider these accessory species here. Users should firstly look at the diagnoses of the species groups given above and simultaneously compare the images of the species which are given for each species in three visual positions and in order of relatedness. This will allow a good entry into the issue.

1

• Antennae with 11 segments. Collective length of the three apical antennal segments 57–63% of whole funiculus length. Anterior part of postpetiole in dorsal view conic. Petiole with a very long peduncle and well-developed node => 2
• Antennae with 12 segments. Collective length of the four apical antennal segments 57–63% of whole funiculus length. Anterior part of postpetiole in dorsal view not conic => 3

2

return to couplet #1

• Occurring west of the Wallace Line. Head shorter, CL/CW 1.057–1.157. Petiole node higher, (PeH/CS 0.323–0.352), in lateral view more produced frontad, with concave anterior profile, the dorsal profile and caudal slope form a continuous convexity (Figure 26B). Pubescence on 1st gaster tergite shorter, PLG/CS 4.52–6.08% (Figure 26) => Cardiocondyla sima
• Occurring east of the Wallace Line. Head longer (CL/CW 1.167–1.196). Petiole node lower (PeH/CS 0.304–0.321, in lateral view slightly produced caudad (Figure 27B). Pubescence on 1st gaster tergite longer, PLG/CS 5.93–6.93% (Figure 27) => Cardiocondyla papuana

Figure 26. Cardiocondyla sima: head in dorsal view (A), lateral view (B), dorsal view (C).

3

return to couplet #1

• Metanotal depression very deep (MGr/CS 5.5–6.6%) and with an extremely steep posterior slope that forms with the anterior slope a distinct angle of 90–100° (Figure 25B). Scape very short (SL/CS 0.769–0.805), petiole very narrow (PeW/CS 0.218–0.242). Postpetiolar sternite almost flat, only with suggested and very rounded anterolateral corners (Figure 25) => Cardiocondyla sulcata
• Metanotal depression less developed or absent, if similarly deep than scape much longer (SL/CS > 0.85) or petiole much wider (PeW/CS > 0.25) => 4

Figure 25. Cardiocondyla sulcata, paratype: head in dorsal view (A), lateral view (B), dorsal view (C).

4

return to couplet #3

• Pronotal corners in dorsal view very prominent, sharp, forming a distinct angle of 70–80° (Figures 22C, 23C and 24C). Spine base narrower (SPBA/CS 0.237–0.368) => 5
• Pronotal corners in dorsal view developed but blunt (Figures 13C, 14C, 18C, 19C, 20C and 21C). Spine base very broad (SPBA/CS 0.322–0.388)=> 7
• Pronotal corners in dorsal view absent => 12

Figure 22. Cardiocondyla thoracica: dorsal view.

Figure 23. Cardiocondyla paradoxa: dorsal view.

Figure 24. Cardiocondyla subspina, paratype: dorsal view.

Figure 13. Cardiocondyla latifrons: dorsal view.

Figure 14. Cardiocondyla micropila, holotype: dorsal view.

Figure 18. Cardiocondyla wheeleri, syntype: dorsal view.

Figure 19. Cardiocondyla excavata, holotype: dorsal view.

Figure 20. Cardiocondyla goroka, paratype: dorsal view.

Figure 21. Cardiocondyla nigrocerea: dorsal view.

5

return to couplet #4

• Scape extremely long, SL/CS > 0.92. Metanotal groove deep, MGr/CS > 4%. Petiole very elongated and very low, PeH/CS < 0.31 (Figure 23) => Cardiocondyla paradoxa
• Scape much shorter, SL/CS < 0.92. Metanotal groove shallower or absent, MGr/CS < 4%. Petiole not extremely elongated and higher, PeH/CS > 0.31 => 6

Figure 23. Cardiocondyla paradoxa: head in dorsal view (A), lateral view (B), dorsal view (C).

6

return to couplet #5

• Dorsal surface of head shining, with scattered foveolae the distance of which is much larger than their diameter. Anterior clypeal margin deeply excavated (Figure 22A). Anterior postpetiolar sternite in lateral view not with a sharp corner (Figure 22B). Head blackish brown (Figure 22) => Cardiocondyla thoracica
• Dorsal surface of head not shining, with more densely packed foveolae the distance of which is as large or smaller than their diameter. Anterior clypeal margin not deeply excavated (Figure 24A). Anterior postpetiolar sternite in lateral view with a sharp corner (Figure 24D). Head yellowish (Figure 24) => Cardiocondyla subspina

Figure 22. Cardiocondyla thoracica: head in dorsal view (A), lateral view (B), dorsal view (C), vertex median of the eye (D).
Figure 24. Cardiocondyla subspina, paratype: head in dorsal view (A), lateral view (B), dorsal view (C), waist in lateral view (D).

7

return to couplet #4

• Vertex and dorsal mesosoma with very deep foveolae many of which show an inner structure reminiscent of a three- or four-leafed cloverleaf (Figures 13D and 14D). Frons wider, FRS/CS 0.309–0.357. Postpetiole narrower, PpW/CS 0.428–0.531 => 8
• Vertex and dorsal mesosoma with shallower, bicoronate foveolae lacking an inner structure reminiscent of a three- or four-leafed cloverleaf. Frons narrower, FRS/CS 0.259–0.289. Postpetiole wider, PpW/CS 0.513–0.569 => 9

Figure 13. Cardiocondyla latifrons: vertex median of the eye (D).

Figure 14. Cardiocondyla micropila, holotype: vertex median of the eye (D).

8

return to couplet #7

• Whole body rather concolorous dirty to blackish brown. With all measurements in mm, discriminant 39.855∗CW + 32.809∗SPBA − 129.082∗PpH + 505.05∗PLG − 11.363 > 0 [error 0% in 61 individuals] (Figure 13) => Cardiocondyla latifrons
• Whole body concolorous yellowish. Discriminant < 0 [error 0% in 70 individuals] (Figures 14) => Cardiocondyla micropila

Figure 13. Cardiocondyla latifrons: head in dorsal view (A), lateral view (B), dorsal view (C), vertex median of the eye (D).
Figure 14. Cardiocondyla micropila, holotype: head in dorsal view (A), lateral view (B), dorsal view (C), vertex median of the eye (D).

9

return to couplet #7

• Petiole very high (PeH/CS > 0.365), its node in profile nearly rectangular, with a long and rather straight dorsal profile. Dorsal mesosomal profile from pronotum to spine tips rather continuously straight (Figure 21B). Scape short, SL/CS < 0.84, ratio SL/PeH∗PpH < 0.58 (Figure 21) => Cardiocondyla nigrocerea
• Petiole lower (PeH/CS < 0.365), not quasi rectangular in profile with the dorsum of its node convex. Dorsal mesosomal profile from pronotum to spine tips not continuously straight. Scape longer, SL/CS > 0.84, ratio SL/PeH∗PpH > 0.58 => 10

Figure 21. Cardiocondyla nigrocerea: head in dorsal view: (A), lateral view (B), dorsal view (C).

10

return to couplet #9

• Anterior clypeal margin strongly concave (Figure 19A). Head short, CL/CW 1.104–1.111, spine base narrower, SPBA/CS 0.341–0.353. Central vertex only foveolate, not with fine longitudinal carinulae (Figure 19) => Cardiocondyla excavata
• Anterior clypeal margin not concave (Figures 18A and 20A). Head longer, CL/CW 1.130–1.155. Spine base broader, SPBA/CS 0.362–0.375. Central vertex in addition to abundant foveolae finely longitudinally carinulate => 11

Figure 19. Cardiocondyla excavata, holotype: head in dorsal view (A), lateral view (B), dorsal view (C).

Figure 18. Cardiocondyla wheeleri, syntype: head in dorsal view.

Figure 20. Cardiocondyla goroka, paratype: lateral view.

11

return to couplet #10

• Propodeal spines longer, SP/CS 0.389–0.418. Body size smaller, CS < 0.55 mm. Anterior face of petiole in profile feebly concave (Figure 18) => Cardiocondyla wheeleri
• Propodeal spines shorter, SP/CS 0.323–0.351. Body size larger, CS > 0.55 mm. Anterior face of petiole in profile more concave (Figure 20) => Cardiocondyla goroka

Figure 18. Cardiocondyla wheeleri, syntype: head in dorsal view (A), lateral view (B), dorsal view (C).
Figure 20. Cardiocondyla goroka, paratype: head in dorsal view (A), lateral view (B), dorsal view (C).

12

return to couplet #4

• Mesosoma thickset and hunchbacked, its dorsal profile strongly and evenly convex (Figure 10B), ratio mesosoma length without neck shield against mesosoma height 1.95–2.12. Postpetiolar sternite bilobate or bicuspidate (Figures 11D and 12D) => 13
• Mesosoma more slender and not hunchbacked, its dorsal profile not strongly and evenly convex, ratio mesosoma length without neck shield against mesosoma height 2.30–2.67. Postpetiolar sternite flat, not bilobate or bicuspidate (except for Cardiocondyla allonivalis) => 16

Figure 10. Cardiocondyla argentea, paratype: lateral view.

Figure 11. Cardiocondyla semiargentea, paratype: waist in frontolateral view.

Figure 12. Cardiocondyla argyrotricha, holotype: waist in lateral view.

13

return to couplet #12

• Lateral head at horizontal level of eye with an longitudinal, dark brown ribbon that is as broad as the eye; this ribbon is flanked below and above by broad bands without any pigment. Petiole without any pigmentation (appearing whitish in dead, dry specimens). Propodeal spines shorter, SP/CS < 0.235, frons narrower FRS/CS < 0.260 (Figure 15) => Cardiocondyla pirata
• Lateral head without ribbons and bands. Petiole at least with light yellowish pigmentation. Propodeal spines longer, SP/CS > 0.235, frons broader, FRS/CS > 0.260 => 14

Figure 15. Cardiocondyla pirata: head in dorsal view (A), lateral view (B), dorsal view (C).

14

return to couplet #13

• Head very short, CL/CW 1.038–1.065. Dorsum of petiole node in profile semicircular (Figure 10B). Silvery pubescence hairs on head flat (Figure 10) => Cardiocondyla argentea
• Head longer, CL/CW 1.094–1.182. Dorsum of petiole node in profile broadly convex, not semicircular (Figures 11B and 12B) => 15

Figure 10. Cardiocondyla argentea, paratype: head in dorsal view (A), lateral view (B), dorsal view (C), vertex median of the eye (D).
Figure 11. Cardiocondyla semiargentea, paratype: lateral view.	Figure 12. Cardiocondyla argyrotricha, holotype: lateral view.

15

return to couplet #14

• Mesosoma in lateral view more humpbacked and thickset, without any suggestion of a metanotal depression (Figure 11B). Frons narrower, FRS/CS 0.261–0.285. Overall head shape in dorsal view more rectangular (Figure 11A). Occurring east of the Wallace Line (Figure 11) => Cardiocondyla semiargentea
• Mesosoma in lateral view less humpbacked and slender, sometimes with a suggestion of a metanotal depression (Figure 12B). Frons wider, FRS/CS 0.292–0.319. Overall head shape in dorsal view more oval (Figure 12A). Occurring west of the Wallace Line (Figure 12) => Cardiocondyla argyrotricha

Figure 11. Cardiocondyla semiargentea, paratype, head in dorsal view (A), lateral view (B), dorsal view (C) waist in frontolateral view (D).
Figure 12. Cardiocondyla argyrotricha, holotype: head in dorsal view(A), lateral view (B), dorsal view (C), waist in lateral view (D).

16

return to couplet #12

• Frons wider, FRS/CS 0.271–0.314. Propodeal spines longer, SP/CS 0.178–0.217. Postpetiole much higher, PpH/CS 0.310–0.361 => 17
• Frons narrower, FRS/CS 0.221–0.261. Propodeal spines shorter, SP/CS 0.089–0.156. Postpetiole much lower, PpH/CS 0.223–0.294 => 18

17

return to couplet #16

• Postpetiolar sternite in profile flat without any anterolateral corners (Figure 16) => Cardiocondyla nivalis
• Postpetiolar sternite in profile strongly bulging; this bulge is formed by bilateral lobes strongly protruding compared to median level of sternite; these lobes appear as corners in anterolateral view (Figure 17) => Cardiocondyla allonivalis

Figure 16. Cardiocondyla nivalis: head in dorsal view (A), lateral view (B), dorsal view (C), vertex median of the eye (D).
Figure 17. Cardiocondyla allonivalis, holotype: head in dorsal view (A), lateral view (B), dorsal view (C), waist in frontolateral view (D).

18

return to couplet #16

• Absolute scape length much larger, SL 385–443 µm (Figure 9) => Cardiocondyla parvinoda
• Absolute scape length much smaller, SL 270–354 µm => 19

Figure 9. Cardiocondyla parvinoda: head in dorsal view (A), lateral view (B), dorsal view (C).

19

return to couplet #18

• Posterior part of vertex glabrous with small foveolae of 7 µm mean diameter and distance between foveolae larger than their diameter. Mesosoma shining with very weak reticulate microsculpture and propodeal spines reduced to blunt dents (Figure 8) => Cardiocondyla britteni
• Posterior part of vertex matt, with strongly developed microsculpture and foveolae of at least 12 µm mean diameter. Mesosoma not shiny, with well developed reticulate microsculpture and sharper, longer propodeal spines => 20

Figure 8. Cardiocondyla britteni, holotype (specimen CASENT0901496 from www.antweb.org, photo Ryan Perry): head in dorsal view (A), lateral view (B), dorsal view (C).

20

return to couplet #19

• Petiole very low (PeH/CS 0.273–0.284), in profile with a flat convex node (Figure 5B). Head short, CL/CW 1.167–1.199. First gaster tergite shiny, its basal part may show a barely visible microreticulum (Figure 5) => Cardiocondyla schulzi
• Petiole higher (PeH/CS 0.283–0.368), in profile with a more developed node. If petiole shape similar (opaca), then CL/CW much larger and surfaces of gaster tergites completely matt, very finely and densely longitudinally shagreened => 21

Figure 5. Cardiocondyla schulzi, holotype: head in dorsal view (A), lateral view (B), dorsal view (C).

21

return to couplet #20

• Scape long, SL/CS 0.836. Petiole low, PeH/CS 0.283. All body surfaces completely matt because of a dense carinulate-foveolate microsculpture (Figure 7) => Cardiocondyla opaca
• Scape much shorter, SL/CS 0.725–0.790. Petiole higher, PeH/CS 0.308–0.368 => 22

Figure 7. Cardiocondyla opaca, holotype: head in dorsal view (A), lateral view (B), dorsal view (C).

22

return to couplet #21

• Exposed surfaces of gaster tergites completely matt, very finely and densely shagreened (Figure 6) => Cardiocondyla carbonaria
• Exposed surfaces of gaster tergites shiny (Figures 2–4) => Cardiocondyla minutior, Cardiocondyla goa, Cardiocondyla tjibodana

Figure 6. Cardiocondyla carbonaria, holotype (specimen CASENT0908337 from www.antweb.org, photo Will Ericson): head in dorsal view (A); lateral view (B); dorsal view (C).
Figure 2. Cardiocondyla minutior: head in dorsal view (A), lateral view (B), dorsal view (C).
Figure 4. Cardiocondyla tjibodana: head in dorsal view (A), lateral view (B) dorsal view (C).

Determination of these three species only possible by linear discriminant analysis (LDA). It is recommended to record the following characters in mm: CL, CW, SL, EYE, FRS, SP, PpW, PeH, PpH and PLG and then running the test specimens as wild-cards in a LDA against the data given in of supplementary information Table S1. The total classification error in 210 worker individuals in Table S1 is 2.4%.

References

• Seifert, B. 2022. The ant genus Cardiocondyla (Hymenoptera: Formicidae): The species groups with Oriental and Australasian origin. Diversity 15, 25 (doi:10.3390/d15010025).