Dicharax fraterculus (Bavay & Dautzenberg, 1900)

Asami, Takahiro, 2017, Revision of the Alycaeidae of China, Laos and Vietnam (Gastropoda: Cyclophoroidea) I: The genera Dicharax and Metalycaeus, Zootaxa 4331 (1), pp. 1-124 : 62-64

Dicharax fraterculus (Bavay & Dautzenberg, 1900)

FIGUrE 41 .

Alycaeus (Charax) fraterculus Bavay & Dautzenberg, 1900a: 120 .

Alycaeus (Charax) fraterculus Bavay & Dautzenberg, 1900b: 457 –458, pl. 11, figs 11–14. Alycaeus (Dicharax) fraterculus — Kobelt, 1902: 370.

Types examined. MNHN IM- 2012-27 168 (TypE spECImEN, prObabLy HOLOTypE), HaUT TONkIN, LEG. MEssaGEr.

Museum material examined. MNHN IM-2012-27037 /7, TONkIN, LEG. MEssaGEr ; MNHN IM-2012-27026/6, HT-TONkIN, COLL. STaadT 1969; MNHN IM-2012-27025/4, HaUT-TONkIN, COLL. DENIs 1945; MNHN IM-2012-27031/ 4, HT-TONkIN, LEG. MEssaGEr, COLL. LETELLIEr 1949; MNHN IM-2012-27038 /38 (sOmE Of THE jUvENILEs arE vEry wEaTHErEd), TONkIN, LEG. MEssaGEr ; MNHN IM-2012-27032/2, QUaNG HUyEN, COLL. FIsCHEr; SMF 192349 /1, TONkIN, BaC-KaN, LEG. MEssaGEr , COLL. C. BOsCH Ex COLL. H. ROLLE; SMF 192349 /1, TONkIN, BaC-KaN, LEG. MEssaGEr , COLL. C. BOsCH Ex COLL. H. ROLLE; NHMUK 1901.4.25.33–34/2, TONkIN, prObabLy LEG. MEssaGEr ; NHMUK 1904.8.1.13–14/2, TONkIN, (rarIssImE) ; NHMUK 1910.1.21.11–12/2, TONkIN, THaT KHé, prObabLy LEG. MEssaGEr ; NHMUK 20150479 /5, TONkIN, V.W. MaCANdrEw COLL .; NHMUK 20150480 /2, TONkIN, E.R. SykEs COLL., 1954.

New material examined. HE/5, PGB/1 ( Ex COLL. HEmmEN), Vn 10-68 VIETNam, CaO BằNG PrOvINCE, rIGHT Off OLd rd., Ca. 33 km frOm CaO BằNG TO ĐôNG KHê, 22°27.547'N, 106°22.331'E, LEG. CH. & J. HEmmEN , 26 Mar 2010; HE/6, Vn 10-69 VIETNam, CaO BằNG PrOvINCE, Ca. 34.5 km frOm CaO BằNG TO ĐôNG KHê (LEfT Off NEw rd.), 22°27.439'N, 106°24.994'E, LEG. CH. & J. HEmmEN , 26 Mar 2010; HE/2 + 1 jUvENILE sHELL, Vn 09-21 VIETNam, CaO BaNG PrOvINCE, Ca . 38.8 km S Of CaO BaNG, Ca. 508 m, 22°27.445'N, 106°24.023'E, LEG. CH. & J. HEmmEN , 15 OCT 2009; HE/4, 2011/85 VIETNam, CaO BằNG PrOvINCE, CaO BằNG 34.5 km TOwards ĐôNG KHê, LEfT sIdE Of THE rOad, 500 m, 22°27.487'N, 106°25.047'E, LEG. A. HUNyadI , 15 NOv 2011; HA/3, 2011/84 VIETNam, CaO BằNG PrOvINCE, ĐôNG KHê 3 km TOwards ĐèO LũNG PHầy, rIGHT sIdE Of THE rOad, 390 m, 22°24.223'N, 106°25.937'E, LEG. A. HUNyadI , 15 NOv 2011; HE/1, Vn 11-159 VIETNam, LạNG SƠN PrOvINCE, aT km 74.8 ON rOad 1B, ĐồNG ĐăNG TO THáI NGUyêN (8 km S BắC SƠN), 21°54.543'N, 106°17.298'E, LEG. CH. HEmmEN, 0 2 Apr 2011; HE/8, PGB/2 (Ex COLL. HEmmEN), Vn 10-76 VIETNam , SƠN La PrOvINCE , Ca. 32 km frOm MộC CHâU TO Hà N ộI (OLd rOad), 20°47.351'N, 104°50.063'E, LEG. CH. & J. HEmmEN, 0 2 Apr 2010.

Diagnosis. A mEdIUm sIzEd spECIEs wITH TypICaL Dicharax - TypE rIbs ON R2, GLOssy R1 aNd R3, LONG R3 wITH bLUNT swELLING aNd sTrONGLy CrENULaTEd INNEr LIp.

Description. SHELL ( FIGUrE 41A ) bEIGE; sHELL OUTLINE sLIGHTLy OvaL frOm dOrsaL vIEw, spIrE aLmOsT fLaT, bOdy wHOrL rOUNdEd; prOTOCONCH LOw, CONsIsTING Of sLIGHTLy mOrE THaN 1.5 wHOrLs, GLOssy; R1 CONsIsTs Of sLIGHTLy mOrE THaN 1.75 wHOrLs, COarsELy, raTHEr IrrEGULarLy rIbbEd, rIbs wEakEr ON EdGE Of bOdy wHOrL (HErE THE sHELL Is aLmOsT smOOTH); TraNsITION bETwEEN R1 aNd R2 CLEarLy vIsIbLE dUE TO sUddEN INCrEasE Of rIb dENsITy; LENGTH Of R2 aNd R3 LEss THaN a HaLf wHOrL COmbINEd (abOUT 150–160 dEGrEEs), R2 sLIGHTLy sHOrTEr THaN R3; R2 vEry fINELy aNd dENsELy rIbbEd, rIbs LOw, CUrvEd TOwards THE apErTUrE; CrOss-sECTIONaL vIEw Of R2 COULd NOT bE ExamINEd, bUT prObabLy sImILar TO THOsE Of THE OTHEr spECIEs HavING CUrvEd rIbs; TraNsITION bETwEEN R2 aNd R3 CLEarLy vIsIbLE bECaUsE rIbbING sTOps aT OrIGIN Of TUbE, R3 aLmOsT smOOTH, ONLy wITH barELy vIsIbLE, IrrEGULar GrOwTH LINEs; CONsTrICTION bETwEEN R2 aNd R3 NOT CONspICUOUs; apErTUrE ExTErNaLLy sLIGHTLy, INTErNaLLy sTrONGLy CrENULaTEd by HavING fIvE sTrONG kNOTs; OUTEr LIp NOT vEry HIGH bUT sHarp, sLIGHTLy rEfLECTEd, sITUaTEd CLOsE TO THE apErTUrE, INNEr LIp THICkENEd.

Measurements (in mm). D = 4.6–5.4, H = 2.1–3.0 (N = 22, spECImENs frOm dIffErENT sampLEs).

Operculum. THE OpErCULUm Of THE HOLOTypE Is aLmOsT smOOTH, bUT THaT Of sampLE MNHN IM-2012-27038, wHICH Is IdENTICaL wITH THE TypE CONCHOLOGICaLLy, Has CLOsELy COILEd OpErCULUm (ObsErvEd IN 3 spECImENs). THE INNEr sUrfaCE Of THE OpErCULUm COULd NOT bE ExamINEd.

Variation in specimens. THE sHELLs frOm sOUTHErN SON La PrOvINCE ( VN 10-76) HavE sLIGHTLy wIdEr UmbILICUs THaN THE ONEs frOm LaNG SON aNd CaO BaNG PrOvINCEs, aNd THE dIsTaNCE bETwEEN THE INNEr aNd OUTEr pErIsTOmEs Is smaLLEr ( THE pErIsTOmE Is OvEraLL THINNEr). THE pOpULaTIONs frOm LaNG SON aNd CaO BaNG PrOvINCEs sHOw NO NOTabLE varIabILITy IN TErms Of sHELL CHaraCTErs.

Differential diagnosis. Dicharax fraterculus dIffErs frOm D. anthostoma by THE smaLLEr, fLaTTEr sHELL, smOOTHEr R1 aNd ENTIrELy smOOTH R3, wEakEr CONsTrICTION aNd swELLING ON R3, OUTEr LIp sITUaTEd CLOsEr TO THE INNEr LIp, wHICH Has mOrE CUrvEd LObEs. SEE aLsO REmarks.

Distribution. THIs spECIEs Is kNOwN frOm NOrTHErN VIETNam (sOUTHErN SON La, LaNG SON aNd QUaNG UyEN PrOvINCEs) ( FIGUrE 32 ).

Remarks. INITIaLLy wE CONsIdErEd syNONymIzING Alycaeus fraterculus wITH Dicharax fimbriatus , bECaUsE IT CaN bE INTErprETEd THaT THE fOrmEr faLLs wITHIN THE HUGE mOrpHOLOGICaL varIabILITy Of THE wIdEsprEad aNd CONCHOLOGICaLLy dIvErsE LaTTEr. WE dECIdEd TO kEEp D. fraterculus as a sEparaTE spECIEs bECaUsE D. fraterculus Has CONsErvaTIvE aNd CLEarLy rECOGNIzabLE TraITs (COmbINaTION Of sTrONGLy CrENULaTEd pErIsTOmE; GLOssy R1 aNd R3; LONG R2–R3, bLUNT swELLING ON R3), aNd THE raNGEs Of D. fraterculus aNd D. fimbriatus OvErLap wITHOUT mOrpHOLOGICaLLy INTErmEdIaTE fOrms.

Figures

FIGURE 32. Distribution of Dicharax species. Triangle: Dicharax fraterculus (Bavay & Dautzenberg, 1900); Circle: Dicharax depressus (Bavay & Dautzenberg, 1912).

FIGURE 41. Shells of Dicharax fraterculus (Bavay & Dautzenberg, 1900). A. holotype (MNHN IM- 2012 - 27168). B. Vn 10 - 76. Scale represents 5 mm. All photos: B. Páll-Gergely.