Dicharax ellipticus, 2017

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 : 23-25

Dicharax (?) ellipticus Páll-Gergely n. sp.

FIGUrEs 15A–B , 16 .

Type material. HOLOTypE RMNH 5004014 , MAA7 VIETNam, QUaNG NINH PrOvINCE, Ha LONG Bay arEa , TIEN ONG CavE ON HaNG TraI IsLaNd, COLLECTEd INsIdE THE CavE, 20°48.96'N, 107°07.33'E, LEG. W. J.M. MaassEN, 0 6 SEp 2003 (LOCaLITy COdE: WMVT.0328); HE/1 paraTypE, Vn 11-104 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 .

Etymology. THE spECIfIC EpITHET rEfErs TO THE ELLIpTICaL OUTLINE Of THE HOLOTypE.

Diagnosis. A vEry smaLL spECIEs wITH fLaT R2 aNd rOUNdEd pErIsTOmE wITH CONspICUOUsLy THICkENEd basaL LIp.

Description of the holotype. SHELL GLOssy, TraNsparENT, COLOUrLEss; sHELL OUTLINE OvaL frOm dOrsaL vIEw, sHapE Of LasT HaLf wHOrL CONspICUOUsLy sIGmOId (THE dOrsaL sUrfaCE Of R3 apprOaCHEs THE LEvEL Of THE prOTOCONCH) rEsULTING IN a NEarLy fLaT sHELL UNUsUaL fOr THE GENUs; bOdy wHOrL rOUNdEd; prOTOCONCH LOw, smOOTH, GLOssy; bOUNdary bETwEEN prOTOCONCH aNd TELEOCONCH NOT vIsIbLE, THEIr LENGTH apprOx. 2.5 wHOrLs COmbINEd; bOUNdary bETwEEN R1 aNd R2 NOT CONspICUOUs, bECaUsE R2 aLsO ENTIrELy smOOTH, wITH NarrOw LIGHT (= mICrOTUNNELs) aNd THICk dark (= arEa bETwEEN THE mICrOTUNNELs) TraNsvErsE sTrIpEs aLTErNaTE; R2 ( FIGUrEs 16B–D ) vEry sHOrT, wITH aLTOGETHEr 13 mICrOTUNNELs; TUbE CONspICUOUsLy THICkENEd aNd ELEvaTEd frOm THE sUTUrE; R3 apprOx. TwO TImEs LONGEr THaN R2, aLsO GLOssy aNd smOOTH; CONsTrICTION bETwEEN R2 aNd R3 CLEarLy vIsIbLE; R3 wITH bLUNT swELLING; apErTUrE rOUNdEd, pErIsTOmE sLIGHTLy adNaTE TO pENULTImaTE wHOrL; OUTEr pErIsTOmE sLIGHTLy ExpaNdEd ON dOrsaL sIdE bUT NOT rEfLECTEd; vENTraL sIdE sTrONGLy THICkENEd aNd rEfLECTEd (HErE THE EdGEs Of THE TwO LIps arE sITUaTEd far frOm EaCH OTHEr); INNEr pErIsTOmE NOT CONspICUOUs, rELaTIvELy wEak; UmbILICUs pECULIarLy sHapEd dUE TO THE sTraIGHT pOrTION (maINLy THE R2) Of THE LasT HaLf wHOrL.

Measurements (in mm). D = 2.3, H = 1.1 (HOLOTypE); D = 2.7, H = 1.5 (paraTypE).

Operculum. UNkNOwN.

Variation in specimens. BOTH sampLEs THaT arE IdENTIfIEd as Dicharax ellipticus n. sp. CONTaIN a sINGLE sHELL, THErEfOrE THE varIabILITy wITHIN pOpULaTION rEmaINs UNkNOwN. THE sHELL frOm SON La PrOvINCE Is LarGEr THaN THE ONE frOm QUaNG NINH PrOvINCE, Has a mOrE rOUNdEd sHELL aNd a mOrE THICkENEd vENTraL sIdE Of THE pErIsTOmE.

Differential diagnosis. THE COmbINaTION Of THE vEry smaLL sHELL, GLOssy R1, smOOTH R2, aNd THE sIGNIfICaNTLy THICkENEd basaL parT Of THE pErIsTOmE dIsTINGUIsHEs Dicharax ellipticus n. sp. frOm aLL OTHEr aLyCaEId spECIEs Of THE rEGION IN qUEsTION. THE ONLy spECIEs frOm THE rEGION HavING sImILar R2 (ENTIrELy smOOTH sUrfaCE wITH LIGHT aNd dark TraNsvErsE sTrIpEs aLTErNaTE) Is Dicharax (?) moellendorffi . THaT spECIEs Is, HOwEvEr, mUCH LarGEr THaN D. ellipticus n. sp., Has mUCH LONGEr R2 aNd R3, aNd dIffErENT sHELL sHapE. SEE aLsO UNdEr D. abdoui n. sp.

SpECIEs Of sImILar sIzE ( Dicharax parvulus [ MöLLENdOrff, 1887], D. canaliculatus [vON MOELLENdOrff, 1894], D. microdiscus [ MöLLENdOrff, 1887]) wErE dEsCrIbEd frOm MaLaysIa, aNd HavE rEGULarLy rIbbEd R1 aNd LaCk THE wIdENEd basaL parT Of THE pErIsTOmE.

Distribution. THE TwO kNOwN sHELLs wErE COLLECTEd frOm QUaNG NINH aNd SON La PrOvINCEs. THE dIsTaNCE bETwEEN THEsE TwO sITEs Is apprOxImaTELy 260 km ( FIGUrE 7 ).

Remarks. A sHELL fOUNd IN a sampLE Of D. depressus (PaC-KHa, COLL. STaadT, 1969, MNHN IM-2012-27047) Is sImILar TO D. ellipticus n. sp. IN HavING a smOOTH R2, bUT dIffErs frOm IT by THE absENCE Of a THICkENEd basaL pErIsTOmE. IT Is NOT a paraTypE, aNd fUTUrE rEsEarCH sHOULd CLarIfy ITs IdENTITy.

Figures

FIGURE 7. Distribution of narrow range or single-site endemic Dicharax species. Filled circle. Dicharax tangmaiensis (Chen & Zhang, 2001). Filled triangle, top up. Dicharax (?) alticola Páll-Gergely & Hunyadi n. sp. Filled diamond. Dicharax (?) immaculatus Páll-Gergely n. sp. Empty diamond. Dicharax microcostatus Páll-Gergely n. sp., Dicharax micropolitus Páll- Gergely & Hunyadi, n. sp. and Dicharax bison Páll-Gergely & Hunyadi n. sp. Filled triangle, top down. Dicharax robustus Páll-Gergely & Hunyadi, n. sp. Empty triangle, top down. Dicharax draco Páll-Gergely & Hunyadi n. sp. Empty square. Dicharax imitator Páll-Gergely & Hunyadi n. sp. Empty triangle, top up. Dicharax (?) moellendorffi (Kobelt & Möllendorff, 1886). Filled square. Dicharax (?) ellipticus n. sp. Cross. Dicharax (?) abdoui Páll-Gergely n. sp. Empty circle shows the position of Tchen K’eou (Chengkou), which is the type locality of Alycaeus pentagonus Heude, 1886 (synonym of Alycaeus anthostoma Möllendorff, 1885), Dicharax diminutus (Heude, 1885), Dicharax (?) fargesianus (Heude, 1885), Dicharax planorbulus (Heude, 1885), Metalycaeus muciferus (Heude, 1885), Alycaeus dolomiticus Heude, 1890 (synonym of Alycaeus rathouisianus Heude, 1882), Dicharax (?) dolichodeiros (Heude, 1890), Metalycaeus (?) elevatus (Heude, 1886), Metalycaeus (?) expansus (Heude, 1890).

FIGURE 15. Shells of Dicharax species. A. Dicharax (?) ellipticus Páll-Gergely n. sp. (holotype, RMNH 5004014). B. Dicharax (?) cf. ellipticus Páll-Gergely n. sp., Vn 11 - 104. C. Dicharax canaliculatus (von Moellendorff, 1894) (lectotype, SMF 109468); D: Dicharax microdiscus (Möllendorff, 1887) (lectotype, SMF 109496). E. Dicharax parvulus (Möllendorff, 1887) (lectotype, SMF 109507). Scale represents 3 mm. All images: B. Páll-Gergely.

FIGURE 16. SEM images of the holotype (RMNH 5004014) of Dicharax (?) ellipticus Páll-Gergely n. sp. A. whole shell. B – D. R 2. All images: B. Páll-Gergely.