Ptychognathus, Stimpson, 1858

Hsu, Jhih-Wei, Shih, Hsi-Te & Li, Jheng-Jhang, 2022, Description of a new species of brackish-water crab of the genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) from southern Taiwan, Nauplius (e 2022002) 30, pp. 1-11 : 8

Key to the species of Ptychognathus found in Taiwan

1. Carapace quadrate (width = length), anterolateral margin with an orbital tooth and two distinct teeth. .......................................................................... 2

– Carapacesubquadrate(width>length),anterolateral margin with an orbital tooth and one or two distinct teeth. .......................................................................... 4

– Carapacesubquadrate(width>length),anterolateral margin only with an orbital tooth,or with additional one to three indistinct teeth. ................................ 6

2. Outer surface of male cheliped manus with obvious long setae (on base of fingers and tip of immovable finger). .............................. P. pilosus De Man, 1892

– Outer surface of male cheliped manus without obvious long setae. .................................................. 3

3. Supraorbital margins strongly sinuous,posterolateral margins of carapace almost parallel, not divergent posteriorly. ............. P. altimanus ( Rathbun, 1914)

– Supraorbital margins gently sinuous, posterolateral margins of carapace distinctly divergent posteriorly. .............. P. makii Hsu and Shih, 2020

4. Dorsal surface of carapace with short dense setae (especially part near margins). ................................ ....................................................... P. ishii Sakai, 1939

– Dorsal surface of carapace without dense setae. ... ...................................................................................... 5

5. With a row of small granules behind frontal margin; male telson without tuft of setae. ........................... .............................. P. stimpsoni Hsu and Shih, 2020

– Without row of granules behind frontal margin; male telson with a tuft of setae. .... P. aff. barbatus

6. Anterolateral margin of carapace with a very small orbital tooth and three indistinct teeth, orbital tooth significantly smaller than following teeth. ........... .............................................. P. takahasii Sakai, 1939

– Anterolateral margin of carapace only with an orbital tooth, or with an orbital tooth and one or two indistinct teeth. ............................................... 7

7. Carapace broader (approximately 1.3–1.4 times as broad as long); ambulatory legs slender. ............... ................... P. insolitus Osawa and N. K. Ng, 2006

– Carapace narrower(approximately1.2times as broad as long); ambulatory legs short and stout. ........... 8

8. Posterior margins of dactyli and propodi of ambulatory legs with obvious dense tufts of setae. .............................. P. hachijoensis Sakai, 1955

9. Posterior margins of dactyli and propodi of ambulatory legs only sparsely setose. .................... ........................................................... P. sakaii sp. nov.