Palamnaeus silenus Simon, 1884: 361 Heterometrus petersii : Kovařík,2004:32 Heterometrus silenus А Review of Heterometrus in Thailand (Scorpiones: Scorpionidae) Kawai, Kazusa Unnahachote, Thornthan Suttisatid, Yossaphon Tang, Victoria Euscorpius 2023 373 1 25   Heterometrus petersii : Kovařík,2004:32   8LXFQ 2830813 (Simon, 1884) Simon 1884 [928,1362,223,250] Arachnida Scorpionidae Heterometrus Animalia Scorpiones 16 15 Arthropoda species silenus  ( 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 inboth 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 Cambodiaand Vietnam.  COMMENTS.   Distribution of  H. laoticusand  H. silenusin Thailand  Kovařík (2004: 32, 34) listed Bangkok and Prachinburi as the distribution areas of  H. silenusin Thailand(misidentified as  H. petersii), considering them doubtful (as  H. laoticus). Prendini & Loria (2020: 247, 251–252) considered only  H. laoticusoccurs 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 Ratchathaniand Udon Thaniin 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. silenusis endemic to western  H. laoticuslisted by Prendini & Loria (2020), these three Cambodia, bordering the eastern Thailand. The records of H.provinces are probably the records of  H. silenusin reality;  laoticusfrom the east of Thailandare, as confirmed in this therefore, we removed those provinces from the distribution study, in fact  H. silenus. Prendini & Loria (2020: 248, 286) of  H. laoticusin our study. In fact, Prendini & Loria (2020: argued that the Mekong River (in Laosand 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. laoticusin the previous west to Annamite Mountains).  H. silenuswas 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. silenuswas 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. laoticusin those two provinces without not necessarily prevent  H. silenusoccurring 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. laoticusdistribute to the west of the the second author (no specimen collected). Annamite Mountains, individuals of  H. silenuswere also Prendini & Loria (2020: 247)listed Laosand Cambodiacollected on the west side of Mekong River (therefore, it also as the two additional countries where  H. laoticusoccurs is found on the western side of the Annamite Mountains). besides Thailand. Whereas Laosis the typelocality of this We believe that  H. laoticusdoes not occur in Cambodiaand species that lies in the north of Thailand, the record from the records from Cambodiaand southern Thailandare all H.northwestern Cambodia( Siem Reap Province; Prendini &  silenus.   Figures 68–71:  Heterometrus minotaurus, in dorsal (68, 70) and ventral (69, 71) aspects; scale bar = 10 mm. Figures 68–69.Male from Surat Thani, THNHM. Figures 70–71.Female from Surat Thani, THNHM.   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.   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 80–81:  Heterometrus spinifer, in vivo habitus and dorsal aspect. Figure 80.Male from Yala, TUPC. Figure 81.Male from Narathiwat, TUPC.   Figure 82: Arm-span competition between males of  Heterometrus cimrmanifrom Phattalung.   Figures 83: Arm-span competition between males of  Heterometrus spiniferfrom Yala (right) and Narathiwat (left).  Morphological comparison of  H. laoticusand  H. silenus   H. laoticusand  H. silenusare two highly resemblant sister species, but they can be distinguished by the following characters (  H. laoticusvs.  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– Estinterval was wider in  H. laoticusthan 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. laoticusvs.  H. silenus): (1) total length: both 90–125 mm; (2) PTC: both 15–19 insexes; (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 Chanthaburiin this survey showed granular carapace ( Fig. 24) and tergites, and pronounced finger lobes ( Fig. 44, 77), consistent with the characters of  H. silenusand thus confirming the occurrence of this species in Thailand. The female from Chonburialso exhibited numerous granules on its carapace ( Fig. 25) and tergites, confirming the occurrence of  H. silenusin another province of Thailand. On the other hand, a pair of specimens collected from Lamphunwere smooth on carapace ( Figs. 26–27) and tergites, and therefore concluded as  H. laoticus. [816,1029,609,633] LOCALITY, AND 16 15 1 holotype DEPOSITORY 16 15 1 holotype [943,1127,641,665] MNHN 16 15 RS 0023 1 holotype TUPC Thailand 12.816667 Pluang City 1292 102.11667 16 15 1 1 Chanthaburi TUPC Thailand Khao Khitchakut District 102.21667 16 15 1 1 Chanthaburi TUPC Thailand 13.183333 Bang Phra 1291 101.05 Si Racha District 16 15 1 1 Chon Buri TUPC Thailand 16.23 Mahasarakham Province 769 103.23 16 15 1 1 Mahasarakham Province