Heterometrus silenus ( Simon, 1884 )

Kawai, Kazusa, Unnahachote, Thornthan, Suttisatid, Yossaphon & Tang, Victoria, 2023, А Review of Heterometrus in Thailand (Scorpiones: Scorpionidae), Euscorpius 373, pp. 1-25 : 15-21

Heterometrus silenus ( Simon, 1884)

( Figures 8–9 , 16–17 , 24–25 , 34–35 , 44–45 , 54–55 , 76–79 ) http://zoobank.org/urn:lsid:zoobank.org:act:E6CFAE8B-

9696-4A57-B97B-8790C8563C4D

Palamnaeus silenus Simon, 1884: 361 .

Heterometrus petersii: Kovařík,2004:32 , 34(misidentification, part).

Heterometrus silenus (part): Prendini & Loria, 2020: 279– 290, figs. 10, 24C, D, 51E–H, 70C, 72C, 158, 179–183, table 2 (reference list until 2020).

TYPE LOCALITY AND TYPE DEPOSITORY. Phillippines, Mindanao (incorrect) ; MNHN RS 0023 .

MATERIAL EXAMINED. Thailand, Chanthaburi Province, Pluang City , 12°49'N 102°07'E, found dead on the street, 1♂, TUPC ; Khao Khitchakut District : 12°82'N 102°13'E, 1♂, TUPC ; Chonburi Province, Si Racha District, Bang Phra , 13°11′N 101°03'E, 1♀, TUPC ; Mahasarakham Province, 16.23°N 103.23°E, 1♂, TUPC .

DIAGNOSIS (modified from Kovařík, 2004 (as H. petersii ) and Prendini & Loria, 2020). Total length of adults 90–125 mm. Base color of adults uniformly black, cuticular surface weakly lustrous ( Figs. 76–79 ). Carapace surface relatively granular, with obvious granules presented in anteromedian area; dorsal profile rectangular ( Figs. 24–25 ). Tergite lateral surfaces with numerous granules and appear rough ( Figs. 76–79 ). PTC 15– 19 in both sexes. Pedipalp relatively stout and short in both sexes among congeners ( Figs. 76–79 ); chelae of both sexes robust and short, ChL/W: ♂ ♀ 2.0–2.3; FL/CL: ♂ ♀ <0.74. Dorsal surface of chelal manus smooth in both sexes ( Figs. 34–35 ); prodorsal surface scattered with minute spiniform granules ( Figs. 54–55 ); fixed finger shorter than manus ( Figs. 44–45 ). Proximal lobe on cutting edge of movable finger exhibits pronounced sexual dimorphism, being conspicuously stronger in males than in females ( Figs. 44–45 ). Telson in adults reddish black to pitch black ( Figs. 8–9 , 16–17 ).

DISTRIBUTION. This species is distributed in the eastern part of Thailand. This species also is found in Cambodia and Vietnam.

COMMENTS.

Distribution of H. laoticus and H. silenus in Thailand

Kovařík (2004: 32, 34) listed Bangkok and Prachinburi as the distribution areas of H. silenus in Thailand (misidentified as H. petersii ), considering them doubtful (as H. laoticus ). Prendini & Loria (2020: 247, 251–252) considered only H. laoticus occurs in those areas and further reported it from the provinces of Chanthaburi, Chiang Mai, Chonburi, Kamphaeng Phet, Kanchanaburi, Lampang, Lamphun, Loei, Lop Buri, Nakhon Phathom, Nakhon Ratchasima, Nakhon Sawan, Nan, Phetchabun, Pharae, Sakon Nakhon, Tak, Trat, Ubon Ratchathani and Udon Thani in Thailand.

In this survey, specimens were collected from Chanthaburi and Chonburi, and confirmed to be H. silenus . Geographically, the population in Trat is also likely to be conspecific. Hence, Loria, 2020: 251) is most likely to be H. silenus . As stated in of the provinces which were considered as the localities of Prendini & Loria (2020: 286), H. silenus is endemic to western H. laoticus listed by Prendini & Loria (2020), these three Cambodia, bordering the eastern Thailand. The records of H. provinces are probably the records of H. silenus in reality; laoticus from the east of Thailand are, as confirmed in this therefore, we removed those provinces from the distribution study, in fact H. silenus . Prendini & Loria (2020: 248, 286) of H. laoticus in our study. In fact, Prendini & Loria (2020: argued that the Mekong River (in Laos and Cambodia) and 251–252) did not verify the specimens collected from these Annamite Mountains (in Laos) are the geographic barriers areas according to their material list, although they included that delimit the distribution of H. silenus (Mekong River is them as the distribution areas for H. laoticus in the previous west to Annamite Mountains). H. silenus was considered to text ( Prendini & Loria, 2020: 247). Also, they corrected a few be distributed to the east of Annamite Mountains (Prendini regions plotted in figure 158 that were not mentioned in the & Loria, 2020: 248) and blocked by the Mekong River in the text. H. silenus was also collected from Nakhon Pathom and west ( Prendini & Loria, 2020: 286). This is geographically Nakhon Ratchasima in this study, which shows a sympatric confusing as the western delimitation by Mekong River does distribution with H. laoticus in those two provinces without not necessarily prevent H. silenus occurring in the west of clear boundaries. Two provinces, Ratchaburi and Sakon Annamite Mountains. As they also stated (Prendini & Loria, Nakhon, inferred from iNaturalist were further confirmed by 2020: 286), although H. laoticus distribute to the west of the the second author (no specimen collected). Annamite Mountains, individuals of H. silenus were also Prendini & Loria (2020: 247) listed Laos and Cambodia collected on the west side of Mekong River (therefore, it also as the two additional countries where H. laoticus occurs is found on the western side of the Annamite Mountains). besides Thailand. Whereas Laos is the type locality of this We believe that H. laoticus does not occur in Cambodia and species that lies in the north of Thailand, the record from the records from Cambodia and southern Thailand are all H. northwestern Cambodia (Siem Reap Province; Prendini & silenus .

Morphological comparison of H. laoticus and H. silenus

H. laoticus and H. silenus are two highly resemblant sister species, but they can be distinguished by the following characters ( H. laoticus vs. H. silenus ): (1) granulation of carapace: essentially smooth with scarce granules vs. conspicuously granular (especially on the lateral surfaces) ( Figs. 24–27 ); (2) granulation of tergites: smooth and lustrous ( Figs. 72–75 ) vs. granular and matte ( Figs. 76– 79 ); (3) proximal lobe on the cutting edge of pedipalp movable finger: weakly sexual dimorphic vs. strongly sexual dimorphic (more developed in males and stronger than males of H. laoticus ) ( Figs. 44–47 ); (4) dorsal profile of carapace: triangular vs. rectangular ( Figs. 24–27 ). Upon examining the relative position of trichobothria on the chela, it was found that the Et 1 – Est interval was wider in H. laoticus than in H. silenus ( Figs. 54–57 ), although trichobothrial patterns can vary slightly among individuals and regional populations. However, this rule held true for all individuals examined in this study; hence, this method is assumed to be effective for discriminating the two species. Several continuous and discrete morphometrics overlap between the two species ( H. laoticus vs. H. silenus ): (1) total length: both 90–125 mm; (2) PTC: both 15–19 in sexes; (3) FL/CL: both <0.74; (4) ChL/W: 2.0–2.3 vs. 2.0–2.4.

The key characters are the differences in carapace granulation and finger lobe ( Kovařík, 2004: 21, as H. petersii ; Prendini & Loria, 2020: 246, 283, 286). The adult male specimen collected from Chanthaburi in this survey showed granular carapace ( Fig. 24 ) and tergites, and pronounced finger lobes ( Fig. 44 , 77 ), consistent with the characters of H. silenus and thus confirming the occurrence of this species in Thailand. The female from Chonburi also exhibited numerous granules on its carapace ( Fig. 25 ) and tergites, confirming the occurrence of H. silenus in another province of Thailand. On the other hand, a pair of specimens collected from Lamphun were smooth on carapace ( Figs. 26–27 ) and tergites, and therefore concluded as H. laoticus .

Figures

Figures 4–11: Comparison of Heterometrus spp. in Thailand, metasoma and telson in dorsal aspect. Figures 4–5. H. cimrmani, male from Trang (4) and female from Nakhon Si Thammarat (5), THNHM. Figures 6–7. H. minotaurus, male (6) and female from Surat Thani (7), THNHM. Figures 8–9. H. silenus, male from Chanthaburi (8) and female from Chonburi (9), TUPC. Figures 10–11. H. laoticus, male (10) and female from Lamphun (11), TUPC.

Figures 12–19: Comparison of Heterometrus spp. in Thailand, metasoma and telson in ventral aspect. Figures 12–13. H. cimrmani, male from Trang (12) and female from Nakhon Si Thammarat (13), THNHM. Figures 14–15. H. minotaurus, male (14) and female from Surat Thani (15), THNHM. Figures 16–17. H. silenus, male from Chanthaburi (16) and female from Chonburi (17), TUPC. Figures 18–19. H. laoticus, male (18) and female from Lamphun (19), TUPC.

Figures 20–29: Comparison of Heterometrus spp. in Thailand, prosoma in dorsal aspect. Figures 20–21. H. cimrmani, male from Trang (20) and female from Nakhon Si Thammarat (21), THNHM. Figures 22–23. H. minotaurus, male (22) and female from Surat Thani (23), THNHM. Figures 24–25. H. silenus, male from Chanthaburi (24) and female from Chonburi (25), TUPC. Figures 26–27. H. laoticus, male (26) and female from Lamphun (27), TUPC. Figures 28–29. H. spinifer, males from Yala (28) and Narathiwat (29), TUPC.

Figures 30–39: Comparison of Heterometrus spp. in Thailand, chela in dorsal aspect (trichobothria indicated by red circles). Figures 30–31. H. cimrmani, male from Trang (30) and female from Nakhon Si Thammarat (31), THNHM. Figures 32–33. H. minotaurus, male (32) and female from Surat Thani (33), THNHM. Figures 34–35. H. silenus, male from Chanthaburi (34) and female from Chonburi (35), TUPC. Figures 36–37. H. laoticus, male (36) and female from Lamphun (37), TUPC. Figures 28–29. H. spinifer, males from Yala (38) and Narathiwat (39), TUPC.

Figures 40–49: Comparison of Heterometrus spp. in Thailand, chela in external aspect (trichobothria indicated by red circles). Figures 40–41. H. cimrmani, male from Trang (40) and female from Nakhon Si Thammarat (41), THNHM. Figures 42–43. H. minotaurus, male (42) and female from Surat Thani (43), THNHM. Figures 44–45. H. silenus, male from Chanthaburi (44) and female from Chonburi (45), TUPC. Figures 46–47. H. laoticus, male (46) and female from Lamphun (47), TUPC. Figures 48–49. H. spinifer, males from Yala (48) and Narathiwat (49), TUPC.

Figures 50–57: Comparison of Heterometrus spp. in Thailand, chela in ventral aspect (trichobothria indicated by red circles). Figures 50–51. H. cimrmani, male from Trang (50) and female from Nakhon Si Thammarat (51), THNHM. Figures 52–53. H. minotaurus, male (52) and female from Surat Thani (53), THNHM. Figures 54–55. H. silenus, male from Chanthaburi (54) and female from Chonburi (55), TUPC. Figures 56–57. H. laoticus, male (56) and female from Lamphun (57), TUPC.

Figures 76–79: Heterometrus silenus, in dorsal(76, 78) and ventral(77, 79) aspects; scale bar = 10 mm.Figures 76–77. Male from Chanthaburi, TUPC. Figures 78–79. Female from Chonburi, TUPC.

Figures 72–75: Heterometrus laoticus, in dorsal (72, 74) and ventral (73, 75) aspects; scale bar = 10 mm. Figures 72–73. Male from Lamphun, TUPC. Figures 74–75. Female from Lamphun, TUPC.