Dicharax depressus
Creators: name: Asami, Takahiro
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Architaenioglossa
Alycaeidae
Dicharax
Dicharax depressus

description: Dicharax depressus (Bavay & Dautzenberg, 1912)
FIGUrEs 12E–F, 13D, 28E–H, 29E–F, 31A–C.
Alycaeus depressus Bavay & Dautzenberg, 1912: 51 –52, pl. 4, figs 10–13.
Types examined. MNHN IM- 2012-27 165 (TypE spECImEN, prObabLy HOLOTypE), PaC-KHa, LEG. MEssaGEr.
Museum material examined. MNHN IM-2012-27039 (2 sHELLs), PaC-KHa, LEG. MEssaGEr; MNHN IM-2012- 27028/4 (mIxEd sampLE wITH " Dicharax sp.": MNHN IM-2012-27047), PaC-KHa, COLL. STaadT, 1969; MNHN IM- 2012-27030/3, TONkIN, PaC-KHa, COLL. DENIs 1945; SMF 192368/2, TONkIN, COLL. C. BOsCH Ex COLL. H. ROLLE; NHMUK 1910.1.21.13–14/2, TONkIN, PaC KHa, prObabLy LEG. MEssaGEr.
New material examined. HE/1, Vn 10-109 VIETNam, SON La PrOvINCE, E Of SON La, 0.5 km ON sECONdary rOad, 21°15.310'N, 103°59.399'E, LEG. CH. & J. HEmmEN, 10 OCT 2010; HE/3, Vn 12-283 VIETNam, SON La PrOvINCE, rOad NO. 104 PHa KHEN TO MOC THUONG, aT km 12.4, 20°54.054'N, 104°39.522'E, LEG. CH. HEmmEN, 0 3 OCT 2012; HE/1, Vn 12-104 VIETNam, SƠN La PrOvINCE, rIGHT sIdE Off rOad MộC CHâU TO SƠN La, 20°52.567'N, 104°35.310'E, LEG. CH. HEmmEN, 14 OCT 2011; HA/2, 2012/60 VIETNam, SƠN La PrOvINCE, MộC CHâU 5 km TOwards SƠN La, rIGHT sIdE Of THE rOad NO. 6, 755 m, 20°52.551'N, 104°35.318'E, LEG. A. HUNyadI, 0 6 JUNE 2012; DDS/15, DDS2 VIETNam, SON La, VaN HO DIsTrICT, VaN HO COm., LImEsTONE fOrEsTs IN Pa CHE VIL., 1050 m, 20°47'07"N, 104°45'21"E, LEG. Đ.S. Đỗ, 26 OCT 2013; HA/1, 2012/62 VIETNam, SƠN La PrOvINCE, Hà N ộI 156 km TOwards MộC CHâU, rIGHT sIdE Of THE rOad NO. 6, 1100 m, 20°46.085'N, 104°53.888'E, LEG. A. HUNyadI, 0 6 JUNE 2012; HE/1, Vn 12-223 VIETNam, THaNH HOa PrOvINCE, PU LUONG NaTUrE REsErvE, PHO DONG, 20°26.960'N, 105°10.927'E, LEG. CH. HEmmEN, 15 Apr 2012; WM/3, MAA4 VIETNam, THaNH HOa PrOvINCE, PU LUONG NaTIONaL Park, LImEsTONE HILL bEHINd raNGEr sTaTION, 20°26.95'N, 105°10.93'E, LEG. W. J.M. MaassEN, 22 SEp 2003 (LOCaLITy COdE: WMVT.0345); SMF 346380 /3, Ch 1 VIETNam, THaN HOa PrOvINCE, PU LONG NaTIONaL Park, Am vILLaGE, 20°27.39'N, 105°13.65'E, LEG. W. J.M. MaassEN, 21 SEp 2003, Ex COLL. HEmmEN, PGB/1; SMF 346382/1, samE daTa, LEG. HEmmEN, 21 SEp 2003; WM/50, MAA1 samE daTa, LEG. W.J.M. MaassEN, 21 SEp 2003 (LOCaLITy COdE: WMVT.0344), HNHM 99727 /1 (fIGUrEd sHELL), PGB/ 5 (Ex COLL. MaassEN); JUO/1 (sHELL, bOdy IN ETHaNOL, radULa ON dOUbLE-faCEd adHEsIvE TapE), 20080510B VIETNam, NGHE AN PrOvINCE, PU HUONG NaTUrE REsErvE, CON CUONG DIsTrICT, ANH SON, DINH SON, 67 m, 19°01.76055'N, 104°55.92037'E, LEG. K. OHara, K, OkUbO & J.U. OTaNI, 10 May 2008; MNHN IM-2012-27166 /2, 08L06 CENTraL LaOs, XIENG KHOUaNG PrOvINCE, apprOx. 18 km SW Of BaN KO KIENG, apprOx. 22 km SW Of VIENG THONG, ON THE rIGHT sIdE Of Nam KHaN, LImEsTONE, bLaCk sOIL IN LImEsTONE pOCkETs, CLay, UNdEr rOCks aNd LOGs aT basE Of CLIff IN sECONdary fOrEsT, 560 m, 19°54.842'N, 103°14.392'E, LEG. A. AbdOU, I.V. MUraTOv, 28 OCT 2006; MNHN IM-2012- 27165 /4, 34L06 CENTraL LaOs, LUaNG PrabaNG PrOvINCE, apprOx. 6 km N Of PHOU KHOUN, LImEsTONE, CLay, UNdEr rOCks IN dry sECONdary fOrEsT UNdEr aNd abOvE CLIff, 1244 m, 19°29.653'N, 102°24.470'E, LEG. A. AbdOU, I.V. MUraTOv, 16 NOv 2006; MNHN IM-2012-27171 /3, 3L05 NOrTHErN LaOs, PHONGsaLy PrOvINCE, SE Of PHONGsaLy, jUsT S Of UppEr rEaCHEs Of Nam FaN (rIvEr), 1215 m, 21°39.654'N, 102°09.484'E, dry OLd fOrEsT, LEG. A. AbdOU, I.V. MUraTOv, 0 6 Mar 2005; MNHN IM-2012-27169 /1 jUvENILE sHELL, 13L05 NOrTHErN LaOs, PHONGsaLy PrOvINCE, W Of PHONGsaLy E Of Nam HONG (rIvEr), 953 m, 21°41.382'N, 102°04.053'E, Dry OLd fOrEsT, LEG. A. AbdOU, I.V. MUraTOv, 11 Mar 2005; MNHN IM-2012-27168 /20 (mOsTLy wEaTHErEd sHELLs), 11L04 NOrTHErN LaOs, PHONGsaLI PrOvINCE, OLd fOrEsT jUsT sOUTH Of Nam LaN RIvEr, GypsUm, CLay, sTN. 11L04, 21°20.152'N, 101°50.575'E, LEG. A. AbdOU, I.V. MUraTOv & N. PHOTHIHOUmpHaNH, 21 NOv 2004; MNHN IM-2012-27170 /2 (ONE wEaTHErEd aNd ONE jUvENILE sHELL), 13L04 NOrTHErN LaOs, PHONGsaLI PrOvINCE, CLay, yOUNG fOrEsT NOrTH Of Nam LaN RIvEr, sTN. 13L04 21°19.940'N, 101°52.136'E, LEG. A. AbdOU, I.V. MUraTOv & N. PHOTHIHOUmpHaNH, 22 NOv 2004; MNHN IM-2012-27167 /1, 08L04 NOrTHErN LaOs, PHONGsaLI PrOvINCE, OLd fOrEsT aT 24 km rOad pOsT bETwEEN (SE Of) BOUN NEUa aNd (SW Of) PHONGsaLy, 1208 m, 21°36.095'N, 101°58.818'E, LEG. A. AbdOU, I.V. MUraTOv, 18 NOv 2004.
Diagnosis. A smaLL spECIEs wITH TypICaL Dicharax - TypE rIbs ON R2 aNd sIGNIfICaNTLy THICkENEd pErIsTOmE.
Description of the holotype. SHELL (FIGUrE 31A) LIGHT GrEy; sHELL OUTLINE OvaL frOm dOrsaL vIEw, bOdy wHOrL rOUNdEd; prOTOCONCH LOw, CONsIsTING Of aLmOsT 1.5 wHOrLs; R1 CONsIsTs Of 1.75 wHOrLs, GLOssy wITH rEGULar, dENsE rIbs, wHICH GradUaLLy TraNsfOrm TO aN IrrEGULarLy rIbbEd sECTION HavING wIdELy spaCEd rIbs aT ENd Of R1; rIbs LOw aNd bLUNT ON wHOLE sHELL; TraNsITION bETwEEN R1 aNd R2 vEry CLEarLy vIsIbLE; R2 vEry dENsELy rIbbEd; rIbs CUrvEd TOwards apErTUrE; COmbINEd LENGTH Of R2 + R3 Is apprOxImaTELy 100–110 dEGrEEs; R3 sLIGHTLy LONGEr THaN R2; TraNsITION bETwEEN R2 aNd R3 rELaTIvELy CLEarLy vIsIbLE dUE TO THE dIsappEaraNCE Of THE rIbs Of R3; CONsTrICTION bETwEEN R2 aNd R3 sHaLLOw; R3 smOOTH, GLOssy, wITH sOmE wIdELy-spaCEd GrOwTH LINEs ON THE TErmINaL parT; apErTUrE sLIGHTLy TEardrOp-sHapEd; pErIsTOmE vEry THICk OvEraLL; bOUNdary bETwEEN TwO LIps barELy vIsIbLE; OUTEr LIp ExpaNdEd aNd sHarp IN dIrECTION Of UmbILICUs aNd basE Of sHELL, bUT OTHErwIsE raTHEr bLUNT. SEE rEmarks rEGardING THE fINE mOrpHOLOGy Of R2 rIbs.
Measurements (in mm). D = 2.9–4.8, H = 1.7–2.8 (N = 20, sHELLs frOm mULTIpLE sampLEs), sEE aLsO TabLE 2.
Operculum. THE OpErCULUm Of THE HOLOTypE Has a rEddIsH brOwN, LOw, mULTIspIraL LamELLa ON THE OUTEr sUrfaCE. THE OUTEr sUrfaCE Of THE OpErCULUm Of THE 2012/62 spECImEN Had NO LamELLa, ONLy THE mULTIspIraL sTrUCTUrE COULd bE sEEN. THE INNEr sUrfaCE Of sampLE 20080510B was ExamINEd; IT Is CONCavE, wITH aN ELEvaTEd CENTraL NIppLE.
Anatomy. ONE maLE spECImEN was aNaTOmICaLLy ExamINEd (20080510B, COLL. JUO, FIGUrEs 12E–F). THE pENIs Is LarGE aNd rECTaNGULar, sLIGHTLy LONGEr aNd mUCH THICkEr THaN THE rIGHT TENTaCLE.
Radula. THE radULa Of ONE spECImEN was ExamINEd (samE spECImEN THaT was aNaTOmICaLLy ExamINEd). THE TEETH arE vEry sImILar TO THOsE Of Dicharax alticola n. sp., bUT aLL CUsps arE mOrE ELONGaTEd, mOrE sLENdEr aNd mOrE sHarpLy pOINTEd (FIGUrE 13D).
Variation in specimens. POpULaTIONs Of Dicharax depressus sHOw CONsIdErabLE varIabILITy IN TErms Of sHELL sIzE, sCULpTUrE Of R1 (smOOTH TO rEGULarLy, sTrONGLy rIbbEd) aNd THE sHapE Of THE bOdy wHOrL (rOUNdEd TO bLUNTLy kEELEd). TabLE 2 COmpILEs THE varIabLE TraITs aNd THEIr CHaraCTEr sTaTEs IN ExamINEd pOpULaTIONs.
Differential diagnosis. Metalycaeus latecostatus Is sOmEwHaT sImILar TO THE kEELEd aNd rIbbEd pOpULaTIONs Of D. depressus. Metalycaeus latecostatus, HOwEvEr, Has aN ELEvaTEd prOTOCONCH wITH spIraL sTrIaE. SOmE Dicharax depressus pOpULaTIONs arE sympaTrIC wITH sOmE aTypICaL LOOkING D. cristatus pOpULaTIONs. THEy CaN bE dIsTINGUIsHEd by THE sHELL sIzE (D. depressus Is smaLLEr), THE apErTUrE THICkNEss (THICkEr IN D. depressus) aNd THE pOsITION Of THE swELLING ON R3 (sITUaTEd CLOsEr TO THE apErTUrE IN D. cristatus). Dicharax fimbriatus CaN bE dIsTINGUIsHEd frOm D. depressus by THE CrENULaTEd pErIsTOmE. Dicharax depressus Has a THICkEr pErIsTOmE aNd LarGEr sHELL THaN D. diminutus.
THE MaLaysIaN Dicharax diplochilus (MöLLENdOrff, 1887) (ExamINEd sampLE: MaLakka, BUkIT PONdONG, PErak, COLL. MöLLENdOrff, SMF 109476, LECTOTypE) Is sImILar TO D. depressus IN GENEraL sHELL sHapE. THE mOsT CONspICUOUs dIffErENCE bETwEEN THE TwO spECIEs arE THE LENGTH Of R2 (sHOrT IN diplochilus aNd mOdEraTELy LONG IN depressus), aNd THE fOrmaTION Of THE pErIsTOmE. NamELy, IN D. depressus THE INNEr LIp Is prOmINENT, THICkENEd aNd prOTrUdING, aNd THE OUTEr LIp Is ExpaNdEd, raTHEr bLUNT, wHErEas IN D. diplochilus THE INNEr LIp Is NOT CONspICUOUs, rENdErING THE sHarp OUTEr LIp Is dOmINaNT. MaLaysIaN Dicharax oligopleuris (MöLLENdOrff, 1887) (ExamINEd sampLE: MaLakka, PErak, SMF 109226, LECTOTypE aNd SMF 109227, paraLECTOTypEs) Is mUCH smaLLEr THaN D. depressus, aNd aLsO Has sHOrTEr R2.
Distribution. Dicharax depressus Is rEpOrTEd frOm NOrTHErN VIETNam (LaO CaI, SON La, THaNH HOa, NGHE AN prOvINCEs) aNd NOrTHErN LaOs (LUaNG PrabaNG, PHONGsaLI aNd XIENG KHOUaNG prOvINCEs) (FIGUrE 32).
Remarks. THE CrOss sECTIONaL vIEw Of R2 was ExamINEd IN ONE spECImEN (MAA1, FIGUrEs 28G–H): aNTErIOr CrUsT fOrms a sIGNIfICaNTLy ELEvaTEd, HOLLOw rIb, wHICH Has a sTrONGEr aNTErIOr aNd wEakEr pOsTErIOr prOjECTION; aNTErIOr CrUsT fOLds sTrONGLy OvEr THE mUCH wEakEr pOsTErIOr CrUsT; pOsTErIOr CrUsT THICk, IT Is aLsO OCCasIONaLLy HOLLOw; CrOss sECTIONaL vIEw Of THE mICrOTUNNEL Is dEfOrmEd TEardrOp-sHapEd.
Dicharax depressus Has bEEN dEsCrIbEd frOm PaC KHa, NOrTHErN VIETNam, wHICH Is sITUaTEd NEar THE bOrdEr wITH YUNNaN, CHINa. SHELLs Of a NEwLy COLLECTEd pOpULaTION IN THaN HOa PrOvINCE (CH1; apprOx. 250 km frOm THE TypE LOCaLITy), aNd NGHE AN PrOvINCE (20080510B; apprOx. 390 km frOm THE TypE LOCaLITy) arE NEarLy IdENTICaL wITH THE HOLOTypE Of D. depressus. SOmE sampLEs COLLECTEd IN THE VIETNamEsE SON La prOvINCE HavE a raTHEr kEELEd bOdy wHOrL (EspECIaLLy frOm apErTUraL vIEw) aNd HavE vEry sTrONG rIbs ON R1 (FIGUrE 31C). THEsE kEELEd pOpULaTIONs arE LOCaTEd bETwEEN smOOTH sHELLEd pOpULaTIONs. THErEfOrE, wE aTTaCH NO sUbGENErIC dIffErENTIaTION Of THE rIbbEd aNd kEELEd vErsUs THE smOOTH aNd rOUNdEd sHELLEd pOpULaTIONs.
THE spECImEN frOm pOpULaTION 2012/62 Has sOmE spIraL sTrIaTION ON R1, wHICH Has NOT bEEN dETECTEd IN aNy OTHEr Dicharax sampLEs. THIs spIraL sTrIaTION Is LOw aNd mIGHT NOT bE HOmOLOGOUs wITH THE mOrE ELEvaTEd spIraL sTrIaE Of THE GENUs Metalycaeus.
description: Published as part of Asami, Takahiro, 2017, Revision of the Alycaeidae of China, Laos and Vietnam (Gastropoda: Cyclophoroidea) I: The genera Dicharax and Metalycaeus, pp. 1-124 in Zootaxa 4331 (1) on pages 43-45, DOI: 10.11646/zootaxa.4331.1.1, http://zenodo.org/record/1009725