Ptychognathus, Easteranus Rathbun, 1907

Mazancourt, Valentin De, Mazel, Virgile, Marquet, Gérard, Poupin, Joseph & Keith, Philippe, 2024, Integrative taxonomy study of brackish water crabs of the genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) from Polynesia, with description of two new species, Zootaxa 5476 (1), pp. 267-297 : 293

Key to Polynesian species of Ptychognathus

1. Cheliped carpus with spine at inner angle (female not in male). P2–4 merus with spine on superior border distally (male and female). Carapace fronto-orbital width 0.89–0.96 times CW (male and female).................................... 2

– Cheliped carpus of without spine at inner angle (female and male). P2–4 merus without spine on superior border distally (male and female). Carapace fronto-orbital width 0.78–0.90 times CW (male and female)................................. 3

2. Third maxilliped exopod 1.4–1.6 (male), 1.3–1.4 (female) times as long as ischium. P5 dactylus 2.5–3.0 times as long as broad (male and female). Endemic to Marquesas Islands ................................................ P. crassimanus

– Third maxilliped exopod 1.7–1.9 (male), 1.4–1.6 (female) times as long as ischium. P5 dactylus 3.0–3.9 times as long as broad (male and female). Cook Islands, French Polynesia (Gambier, Austral and Society) and Easter Island......... P. easteranus

3. Chelipeds glabrous; very characteristic small tuft of setae at tip of pollex. Third maxilliped exopod 2.1–2.6 (male), 1.6–1.9 (female) times as long as ischium. Widespread....................................................... P. riedelii

– Chelipeds setose; pollex without small tuft of setae at tip. Third maxilliped exopod 0.9–1.3 (male and female) times as long as ischium............................................................................................. 4

4. Anterolateral margin of carapace with only faint lobe after orbital tooth (male and female). Third maxilliped exopod 1.2–1.3 (male), 1.0 (female) times as long as ischium. Endemic to Futuna Island............................. P. similis sp. nov.

– Anterolateral margin of carapace with two distinct teeth after orbital tooth (male). Third maxilliped exopod 0.9–1.0 (male) times as long as ischium. Endemic to Futuna Island.......................................... P. ngankeeae sp. nov.