Cymo, de Haan, 1833

Yuan, Zi-Ming, Jiang, Wei & Sha, Zhong-Li, 2023, A new species of the coral-symbiont crab genus Cymo de Haan, 1833 (Decapoda, Brachyura, Xanthidae) from Nansha Islands, the South China Sea, Zootaxa 5361 (2), pp. 275-286 : 284

Key to species of Cymo

1. Frontal lobes with margin almost straight, lined with denticles, acute granules or spines; dorsal surface of carapace and cheliped carpus and palm with independent, granules and spines....................................................... 2

- Frontal lobes with margin almost straight or concave, lined with coarse, blunt granules of irregular sizes; dorsal surface of carapace, cheliped carpus and palm with similar-shaped granules that are usually in clusters.......................... 8

2. Frontal lobes only with low, flat granules, without prominent spines.................................. C. lanatopodus

- Frontal lobes with prominent spines....................................................................... 3

3. Spines on frontal lobes simple and unbranched, little variation in size; large spine on inner supraorbital angle; cheliped with larger, widely spaced spines or sharp granules............................................................... 4

- Spines on frontal lobes more numerous, noticeably uneven in size; some small acute granules on inner supraorbital angle, often curved or branched; cheliped surface with smaller and denser granules........................................... 6

4. Carapace slightly wider than long, frontal margin spines smaller, cheliped with large spines. Endopodite of maxilliped 1 distinctly concave......................................................................... C. mazu sp. nov.

- Carapace prominently longer than wide, frontal margin spines larger, cheliped with smaller spines; endopodite of maxilliped 1 without concave...................................................................................... 5

5. Frontal margin with slender and sharp frontal spines. Fingers of cheliped white or pale-coloured. Male telson triangular.............................................................................................. C. deplanatus

- Frontal margin with shorter, stout and triangular frontal spines. Fingers of cheliped pigmented brown throughout or almost to tips. Male telson semicircular.................................................................... C. barunae

6. Cheliped fingers white, sometimes with brown or grey bases, always transitioning to white subterminally..... C. andreossyi

- Cheliped fingers uniform black, only showing white at hollowed tip............................................. 7

7. Carapace shorter and wider, with less straight posterior margins, giving it an overall circular shape. The frontal spines short............................................................................................. C. cerasma

- Carapace longer and narrower, with straight posterior margins, giving it an overall hexagonal shape. The frontal spines longer..................................................................................... C. melanodactylus

8. Margin of each frontal lobe concave, front appearing quadrilobed; carapace little longer than wide, subcircular; dorsal surface with 1M, anterior margin of 2M, adjacent regions of anterolateral margins and cardiac regions well demarcated by groups of relatively coarse granules. Outer surface of chelipeds with coarse granules............................ C. quadrilobatus

- Margin of each frontal lobe almost straight, front appearing bilobed; carapace prominently longer than wide, longitudinally ovate; all groups of granules on dorsal surface of carapace and chelipeds comparatively weak.............. C. tuberculatus