Key to Asian Syscia

Key to Asian species of Syscia based on the worker caste, modified from Du et al. (2024).

1

Antennae with 9 segments (Figs 9A, 10D) => 2
Antennae with 11 segments (Figs 2C, 3A, 4D, 5A, 7A) => 3

Du et al. (2024), Fig. 9. Syscia typhla, holotype, worker (FOCOL0804) A. Head in full-face view. B. Label. C. Body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Christiana Klingenberg).
Du et al. (2024), Fig. 10. Syscia zhoui, holotype, worker (GXNU160017). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Mesosoma in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 2. Syscia arcodorsa, holotype, worker (GXNU210848). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 3. Syscia chaladthanyakiji, holotype, worker (THNHM-I-05483). A. Head in full-face view. B. Label. C. Body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Yudthana Samung).
Du et al. (2024), Fig. 4. Syscia humicola, paratype, worker (IZCAS). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 5. Syscia indica, holotype, worker. A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view D. Body in lateral view (images cited from Aswaj et al. 2021).
Du et al. (2024), Fig. 6. Syscia guizhouensis, holotype, worker (No. G160363). A. Head in fullface view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 7. Syscia guizhouensis, worker (No. G160363). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).

2

return to couplet #1

Mesosoma rather elongate, long-ellipsoidal, with lateral sides and anterior margin obviously convex in dorsal view (Fig. 9C); both anterior margin and posterior margin of petiole convex in lateral view (Fig. 9D); posteroventral corner of subpetiolar process blunt rounded in lateral view (Fig. 9D); postpetiole in dorsal view longer than wide (Fig. 9C) => Syscia typhla
Mesosoma rather robust, subrectangular with almost parallel lateral sides, and anterior margin slightly convex in dorsal view (Fig. 10C); both anterior margin and posterior margin of petiole straight in lateral view (Fig. 10D); posteroventral corner of subpetiolar process acute angled in lateral view (Fig. 10D); postpetiole in dorsal view wider than long (Fig. 10B) => Syscia zhoui

Du et al. (2024), Fig. 9. Syscia typhla, holotype, worker (FOCOL0804) A. Head in full-face view. B. Label. C. Body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Christiana Klingenberg).
Du et al. (2024), Fig. 10. Syscia zhoui, holotype, worker (GXNU160017). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Mesosoma in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).

3

return to couplet #1

Head in full-face view oval (Figs 2A, 8B) => 4
Head in full-face view rectangular or trapezoidal (Figs 3B, 4A, 5A, 6A, 7A, 8B) => 5

Du et al. (2024), Fig. 2. Syscia arcodorsa, holotype, worker (GXNU210848). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 3. Syscia chaladthanyakiji, holotype, worker (THNHM-I-05483). A. Head in full-face view. B. Label. C. Body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Yudthana Samung).
Du et al. (2024), Fig. 4. Syscia humicola, paratype, worker (IZCAS). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 5. Syscia indica, holotype, worker. A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view D. Body in lateral view (images cited from Aswaj et al. 2021).
Du et al. (2024), Fig. 6. Syscia guizhouensis, holotype, worker (No. G160363). A. Head in fullface view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 7. Syscia guizhouensis, worker (No. G160363). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 8. Syscia reticularis, holotype, worker (THNHM-I-02624). A. Head in full-face view. B. Label. C. body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Yudthana Samung).

4

return to couplet #3

Body entire reticulate, with deep bottoms (Fig. 8) => Syscia reticularis
Body covered with punctures or shallow fovea (Fig. 2) => Syscia arcodorsa

Du et al. (2024), Fig. 8. Syscia reticularis, holotype, worker (THNHM-I-02624). A. Head in full-face view. B. Label. C. body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Yudthana Samung).
Du et al. (2024), Fig. 2. Syscia arcodorsa, holotype, worker (GXNU210848). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).

5

return to couplet #3

Petiole in dorsal view broader than long (Fig. 3C); in lateral view the front and the back margins of the petiole vertical (Fig. 3A) => Syscia chaladthanyakiji
Petiole in dorsal view longer than broad or as long as broad (Figs 4C, 5B, 6B, 7B); in lateral view the front and the back margins of petiole steep or sloped (Figs 4D, 5D, 6C, 7C) => 6

Du et al. (2024), Fig. 3. Syscia chaladthanyakiji, holotype, worker (THNHM-I-05483). A. Head in full-face view. B. Label. C. Body in dorsal view. D. Body in lateral view (images cited from https://www.antweb.org; imaged by Yudthana Samung).
Du et al. (2024), Fig. 4. Syscia humicola, paratype, worker (IZCAS). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 5. Syscia indica, holotype, worker. A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view D. Body in lateral view (images cited from Aswaj et al. 2021).
Du et al. (2024), Fig. 6. Syscia guizhouensis, holotype, worker (No. G160363). A. Head in fullface view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 7. Syscia guizhouensis, worker (No. G160363). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).

6

return to couplet #5

Subpetiolar process in lateral view subtriangular (Fig. 4C); anterior margin of petiole slightly convex (Fig. 4D) => Syscia humicola
Subpetiolar process in lateral view subrectangular (Figs 5D, 6C, 6B, 7C); anterior margin of petiole slightly concave => 7

Du et al. (2024), Fig. 4. Syscia humicola, paratype, worker (IZCAS). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 5. Syscia indica, holotype, worker. A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view D. Body in lateral view (images cited from Aswaj et al. 2021).
Du et al. (2024), Fig. 6. Syscia guizhouensis, holotype, worker (No. G160363). A. Head in fullface view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 7. Syscia guizhouensis, worker (No. G160363). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).

7

return to couplet #6

Propodeal declivity straight or slightly convex in lateral view (Figs 6–7) => Syscia guizhouensis
Propodeal declivity slightly concave in lateral view (Fig. 5) => Syscia indica

Du et al. (2024), Fig. 6. Syscia guizhouensis, holotype, worker (No. G160363). A. Head in fullface view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 7. Syscia guizhouensis, worker (No. G160363). A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view. D. Body in lateral view (imaged by Zhilin Chen).
Du et al. (2024), Fig. 5. Syscia indica, holotype, worker. A. Head in full-face view. B. Petiole and postpetiole in dorsal view. C. Body in dorsal view D. Body in lateral view (images cited from Aswaj et al. 2021).

References

Du, C., Xu, Z., Chen, Z. 2024. Taxonomic account of the ant genus Syscia Roger, 1816 (Hymenoptera, Formicidae) from Asia, with descriptions of two new species from China. European Journal of Taxonomy 930, 157-181 (doi:10.5852/ejt.2024.930.2491).