Potamoidea Ortmann, 1896

Wong, Kingsley J. H., Ng, Peter K. L., Shih, Hsi-Te & Chan, Benny K. K., 2024, Positive association between PTN polymorphisms and schizophrenia in Northeast Chinese Han population., Zoological Studies 63 (38), pp. 141-149 : 75-76

Superfamily Potamoidea Ortmann, 1896 Family Potamonidae Ortmann, 1896 Subfamily Potamiscinae Bott, 1970

Cryptopotamon anacoluthon ( Kemp, 1918) #

Potamon (Potamon) anacoluthon Kemp, 1918 ; 243, fig. 5; Gee 1926: 161 [list]; Shen 1940a: 229.

Potamon anacoluthon — Hill et al. 1975: 48; Hill et al. 1978: 67.

Potamon hongkongensis — Hill and Phillipps 1981: 144, pl. 49d. [not Potamon (P.) hongkongensis Shen, 1940 (b)].

Cryptopotamon anacoluthon — Ng and Dudgeon 1992: 749, figs. 3B, 4, 5; Dudgeon and Corlett 1994: 53, fig. 6D, pl. 22; Dudgeon 1999: 181, fig. 4.21D; Fellowes et al. 2002: tab. 2 [list]; Dudgeon 2003: 60, 3 unnumb. figs.; Stanton et al. 2017: 9787, figs. 1, 2.

Sinolapotamon anacoluthon — Dai 1999: 152, fig. 79, pl. 9(6); Shih et al. 2009: tab. 1.

Taxonomy: Ng and Dudgeon (1992), Dai (1999: as Sinolapotamon ).

Type: Syntypes in ZSI 9475/10 ( Kemp 1918; Shen 1940a).

Type locality: The Peak, Hong Kong.

Distribution: Probably endemic to Hong Kong and nearby Shenzhen.

Habitat: Freshwater, upper-course streams of gravelly substrate ( Ng and Dudgeon 1992); often found on substrates below running waters of moderate flow, fully aquatic and reluctant to stay, even briefly, out of water.

Remarks: The status of the monotypic genus Cryptopotamon Ng and Dudgeon, 1992 has been questioned. This genus shares close resemblance with Sinolapotamon Tai & Sung, 1975 , but characterized by a more depressed carapace with well-developed epibranchial teeth and distinct epigastric crests (carapace swollen with epibranchial teeth and epigastric crests absent in Sinolapotamon ) (cf. Ng 2000a; Ng et al. 2008). The two genera, however, share a similarly shaped male first gonopod. Dai (1999) treated both genera as synonyms, and both are genetically close (see Shih et al. 2009; Zhu et al. 2010). Lu et al. (2003) recently described a new species, Sinolapotamon cirratum from Guangxi in China. Examining also S. anacoluthon ( Kemp, 1918) sampled from Yangtaishan, Shenzhen, a site relatively near Hong Kong, they argued that both are very close based on genetic data. Ng and Dudgeon (1992) established Cryptopotamon for Kemp’s (1918) species, but Lu et al. (2023) noted that several of the characters used may be only of value at the specific level. While this is true and the genetic differences between Sinalopotamon Tai & Sung, 1975, and Cryptopotamon are close, morphologically, the carapaces of the Sinolapotamon species further to the west in Guangxi ( S. auriculatum Zhu, Naruse & Zhou, 2009 , S. palmatum Zhu, Naruse & Zhou, 2009 , and S. patellifer (Wu, 1934) [type species]) are nevertheless much more convex and smoother, compared to C. anacoluthon and S. cirratum , with the cristae far less developed. For this reason, we prefer to keep the two genera separate for the time being. We have seen specimens of Sinolapotamon cirratum , and we do agree that it is very close to Cryptopotamon anacoluthon . However, we are of the opinion this species should be placed in Cryptopotamon instead.

Nanhaipotamon aculatum Dai, 1997 #

Isolapotamon (Nanhaipotamon) formosanum globosum — Bott 1968a: 125 [part: Hong Kong material only], fig. 10a, b [not Potamon (Geothelphusa) globosum Parisi, 1916 ].

Nanhaipotamon formosanum globosum — Bott 1970b: 196 [part: Hong Kong material only], pls. 41(84) [not Potamon (Geothelphusa) globosum Parisi, 1916 ].

Nanhaipotamon aculatum Dai, 1997: 232 , fig. 11, pl. 2(5); Dai 1999: 124, fig. 62, pl. 7(3).

Taxonomy: Dai (1997 1999).

Type: Holotype ò MMü 1225/ 1 in ZSM.

Type locality: Hong Kong.

Distribution: Probably endemic to Hong Kong and nearby regions of Shenzhen.

Habitat: Freshwater; in burrows on stream banks of altitudes 20 to 100 m ( Dai 1999).

Remarks: This species was described from one male specimen among the collections of freshwater crabs deposited in the Munich, Germany ( ZSM) by Dai (1997) and characterized by the male first gonopod having the mesial subdistal lobe produced as a rounded protrusion (Dai 1997: fig. 11(4, 5)). This form matched illustrations by Bott (1968a 1970b), erroneously under the name I. (N.) formosanum globosum (see Dai (1999); Yeo and Naruse (2007)).

In treating freshwater decapods from Shenzhen, C. Huang and Mao (2021) reported on N. aculatum and N. hongkongense , which were readily identified by their distinct coloration in field (respectively bluish and reddish), showing a distinct west and east distribution immediate north of Hong Kong, with no overlap in between (tab. 1, C Huang and Mao 2021). This observation can possibly correspond to observations in Hong Kong, where bluish crabs were seen only in sites in northwestern New Territories, whereas those from elsewhere in the territory showing colorations along a gradient of red. However, near Tai Tong, Yuen Long, both bluish and reddish crabs had been sampled ( KJHW, unpublished data).

Examining both forms, which show considerable variations in G1 morphologies, particularly of the subdistal lobe, which varies from a rounded protrusion, to a relatively broad, wing-like structure in some reddish forms, we remain uncertain in the precise identification of N. aculatum (see Remarks under N. hongkongense below). We keep this record for Hong Kong until ongoing studies on this species can be completed.

Nanhaipotamon hongkongense (Shen, 1940) #

Potamon (Potamon) hongkongensis Shen, 1940a: 229 [nomen nudum].

Potamon (Potamon) hongkongensis Shen, 1940b: 255 , figs. 1–5.

Potamon globosum — Pretzmann 1963: 367 [not Potamon (Geothelphusa) globosum Parisi, 1916 ].

Potamon hongkongensis — Hill et al. 1975: 48; Hill et al. 1978: 67; Morton and Morton 1983: 214, fig. 11.4(1).

Potamon anacoluthon — Hill and Phillipps 1981: 146, pl. 49e. [not Potamon (P.) anacoluthon Kemp, 1918 ].

Nanhaipotamon hongkongense — Ng and Dudgeon 1992: 744, figs. 1, 2, 3A; Dudgeon and Corlett 1994: 53, fig. 6C, pl. 21; Dai 1997: 224, fig. 7, pl. 2(1); Dai 1999: 118, fig. 58, pl. 6(7); Dudgeon 1999: 181, fig. 4.21C; Fellowes et al. 2002: tab. 2 [list]; Dudgeon 2003: 60, 3 unnumb. figs.; Stanton et al. 2018: 11157, figs. 1, 2.

Taxonomy: Ng and Dudgeon (1992), Dai (1997 1999).

Type: Neotype ò ZRC 1991.1776 (designated by Dai 1997).

Type locality: Nai Chung stream, near Ma On Shan, New Territories, Hong Kong (neotype).

Distribution: Probably endemic to South China: Hong Kong and nearby regions of Shenzhen.

Habitat: Freshwater; secondary forest above 100 m above sea level ( Ng and Dudgeon 1992). These crabs prefer pools of slow-flowing water, often with fallen foliage, under secondary forests with rather tall and dense vegetation cover. Numerous individuals can be found under rock fragments and among crevices of igneous bedrock, to banks of muddy or gritty sediments. The crabs are largely nocturnal, and often spotted at burrow openings. During and shortly after torrential rains, crabs are occasionally found in waterlogged patches.

Remarks: The first Nanhaipotamon species recognized from the vicinity of the Pearl River Delta was Potamon hongkongensis Shen, 1940 collected from an unspecified locality in Hong Kong ( Shen 1940b), the type material of which is considered lost and the species had remained poorly known for many decades. Based on material from several localities (Nai Chung, Tai Po Kau, and Victoria Peak), Ng and Dudgeon (1992) redescribed N. hongkongense in detail. A.-Y. Dai (1999), in her revision of the genus, designated a large male specimen from Nai Chung as neotype of N. hongkongense , and described a new species, N. aculatum , the latter previously reported as I. (N.) formosanum globosum by Bott (1968a 1970b; see Remarks on N. aculatum above).

In recent surveys of Nanhaipotamon in Hong Kong, material we collected from various localities shows substantial variation in the live coloration and G1 morphology. The morphology of the G1 has likewise been shown to be quite variable in other congeneric species, such as N. guangdongense Dai, 1997 (fig. 7, C Huang et al. 2018), N. macau Huang, Wong & Ahyong, 2018 (fig. 5C–E, C Huang et al. 2018) and N. aculatum (fig. 4A–C, C Huang and Mao 2021); so is the case in N. hongkongense (fig. 4D–F, C Huang and Mao 2021; KJHW, unpublished data).

Preliminary genetic analyses performed by the third author showed, based on our local material so far acquired, Nanhaipotamon in vicinity of Hong Kong comprise multiple genetically distinct lineages (see also C Huang et al. 2021). One of these is represented by material from Lamma Island and Lantau Island, marginally distinguishable by subtle but discernable morphological features in addition to those of the gonopods. This study is now in progress.