Ptychognathus species

Hsu, Jhih-Wei & Shih, Hsi-Te, 2020, Romanogobio persus, Zoological Studies 59 (59), pp. 1-13 : 11

Identification of Ptychognathus species via

DNA barcodes

Most species of Ptychognathus have similar morphologies and lack distinct coloration, making it difficult to correctly identify them. For example, the pictures of “ P. affinis ” in Lee (2001: 116) should be P. altimanus and Varuna litterata ; “ P. barbatus ” in Chen (2001: 252) should be P. hachijoensis ; and “ P. cf. hachijoensis ” in Kishino et al. (2001: pl. 1(5)) and “ P. johannae ” in Nakasone and Irei (2003: fig. 50) were confirmed to be a new species, P. insolitus , by Osawa and Ng (2006). DNA barcodes have been applied to help identify several groups of crabs ( Chu et al. 2015). With regard to the genus Ptychognathus , the COI sequences deposited into GenBank are only available for a few species.

Based on the results of our study, the COI sequences are useful for distinguishing the 10 species of Ptychognathus from Taiwan and some from other countries. The interspecific distances are at least 12.2%, which are larger than they are for most species of crabs (see Chu et al. 2015), e.g., the minimum interspecific distance 3.0% among species of Eriocheir sensu lato ( Varunidae ) ( Naser et al. 2012); 3.8% between Hemigrapsus penicillatus (De Haan, 1835) and H. takanoi Asakura & Watanabe, 2005 ( Varunidae ) ( Markert et al. 2014); 1.49% between Leptarma liho (Koller, Liu & Schubart, 2010) and L. paucitorum (Rahayu & Ng, 2009) ( Sesarmidae ) ( Shih et al. 2019b); 3.2% between Sesarmops imperator Ng, Li & Shih, 2020 and S. impressus (H. Milne Edwards, 1837) ( Sesarmidae ) ( Ng et al. 2020); 3.78% between Tubuca urvillei (H. Milne Edwards, 1852) and T. alcocki Shih, Chan & Ng, 2018 ( Ocypodidae ) ( Shih et al. 2018); 4.59% between Austruca citrus Shih & Poupin, 2020 and A. perplexa (H. Milne Edwards, 1852) ( Ocypodidae ) ( Shih and Poupin 2020); 5.63% between Tortomon gejiu Huang, Wang & Shih, 2020 and T. puer Huang, Wang & Shih, 2020 ( Potamidae ) ( Huang et al. 2020); and 6.11% between Tiwaripotamon pingguoense Dai & Naiyanetr, 1994 and T. xiurenense Dai & Naiyanetr, 1994 ( Potamidae ) ( Do et al. 2016).