Dicharax plicilabris ( Möllendorff, 1886 )

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 : 68-70

Dicharax plicilabris ( Möllendorff, 1886)

FIGUrE 33D .

Alycaeus plicilabris Möllendorff, 1886: 167 , pl. 5, fig. 5.

Alycaeus (Chamalycaeus) plicilabris — Kobelt & Möllendorff, 1897: 149. Alycaeus (Chamalycaeus) plicilabris — Kobelt, 1902: 361.

Chamalycaeus plicilabris plicilabris — Yen, 1939: 29, pl. 2, fig. 32.

Chamalycaeus (Chamalycaeus) plicilabris plicilabris — Zilch, 1957: 145, pl. 5, fig. 14.

Types examined. LECTOTypE ( SMF 39229) aNd 4 paraLECTOTypEs ( SMF 39229) Of A. plicilabris CHINa, PrOv. HUNaN , COLL. O. BOETTGEr Ex COLL. MöLLENdOrff.

Diagnosis. A smaLL spECIEs wITH TypICaL Dicharax - TypE rIbs ON R2, bLUNT swELLING ON R3 aNd CrENULaTEd pErIsTOmE.

Description. SHELL ( FIGUrE 33D ) LIGHT OCHrE; sHELL OUTLINE OvaL frOm dOrsaL vIEw, spIrE sLIGHTLy ELEvaTEd, EdGE Of bOdy wHOrL rOUNdEd; prOTOCONCH LOw, CONsIsTING Of 1.5 wHOrLs, raTHEr GLOssy; R1 CONsIsTs Of 1.5–1.75 wHOrLs, rEGULarLy, dENsELy rIbbEd; TraNsITION bETwEEN R1 aNd R2 CLEarLy vIsIbLE dUE TO dENsEr rIbs ON R2; R2 wITH rIbs CUrvING TOwards apErTUrE; CrOss-sECTIONaL vIEw Of R2 COULd NOT bE ExamINEd, bUT IT Is prObabLy sImILar TO THOsE Of THE OTHEr spECIEs HavING CUrvEd rIbs; LENGTH Of R2 aNd R3 Is apprOx. 110–120 dEGrEEs COmbINEd; R3 sLIGHTLy LONGEr THaN R2; TraNsITION bETwEEN R2 aNd R3 CLEarLy vIsIbLE, INdICaTEd by a sLIGHT CONsTrICTION; R3 NEarLy smOOTH, ONLy sOmE IrrEGULar, LOw GrOwTH LINEs arE vIsIbLE; apErTUrE rOUNdEd, bUT ExTErNaLLy sLIGHTLy CrENULaTEd; OUTEr LIp sLIGHTLy rEfLECTEd, sHarp; INNEr LIp THICkENEd, bOUNdary Of TwO LIps Is HardLy vIsIbLE.

Measurements (in mm). D = 3.4–3.5, H = 2.2–2.4 (N = 2, SMF 39230).

Operculum. THE INNEr sUrfaCE COULd NOT bE ExamINEd. THE OUTEr sUrfaCE Is smOOTH, bUT THE mULTIpLE wHOrLs arE vIsIbLE.

Variation in specimens. THE varIabILITy wITHIN THE ONLy kNOwN sampLE Is LOw.

Differential diagnosis. THE OvEraLL sHELL CHaraCTErs (rIb dENsITy, prOpOrTIONs Of rEGIONs) Of D. plicilabris aGrEE wITH THOsE Of D. diminutus , bUT dIffEr IN THE fOLLOwING fEaTUrEs: D. plicilabris Is sLIGHTLy LarGEr THaN D. diminutus , IT Has mOrE ELEvaTEd spIrE (mOrE pOINTEd apEx), LONGEr aNd THINNEr R3, THICkEr aNd wIdEr INNEr LIp aNd kNOTs INsIdE THE apErTUrE. SEE aLsO UNdEr D. fargesianus aNd THE REmarks.

Distribution. ONLy THE OrIGINaL sampLE Is kNOwN frOm THE TypE LOCaLITy.

Remarks. Dicharax plicilabris Is smaLLEr, fLaTTEr, aNd Has a bLUNTEr swELLING ON R3 THaN mOsT D. fimbriatus pOpULaTIONs. THE TwO spECIEs, HOwEvEr, arE pOssIbLy CONspECIfIC bECaUsE bOTH pOssEss a CrENULaTEd pErIsTOmE, aNd sImILarLy LONG R2 aNd R3. If THEy arE CONspECIfIC, THE NamE plicilabris MöLLENdOrff, 1886 Has prIOrITy OvEr fimbriatus Bavay & DaUTzENbErG, 1912 . WE prOvIsIONaLLy kEEp Dicharax plicilabris as a sEparaTE spECIEs bECaUsE Of THE fOLLOwING. Dicharax plicilabris Is mOsT sImILar TO D. diminutus . IT Is pOssIbLE THaT THE CrENULaTEd pErIsTOmE appEarEd INdEpENdENTLy IN D. plicilabris , aNd ITs aNCEsTOrs arE D. diminutus -LIkE spECImENs pOssEssING rOUNdEd apErTUrEs. THUs, THE TwO spECIEs ( diminutus aNd plicilabris ) arE prObabLy CLOsELy rELaTEd, aNd THE sImILarITy wITH D. fimbriatus Is ONLy dUE TO paraLLEL EvOLUTION. THIs HypOTHEsIs Is sUppOrTEd by THE GEOGrapHIC dIsTrIbUTION Of THE THrEE spECIEs IN qUEsTION. MOsT Dicharax fimbriatus spECImENs wE ExamINEd HavE bEEN COLLECTEd IN GUaNGxI, YUNNaN, GUIzHOU prOvINCEs aNd sOUTHErN HUNaN. ALTHOUGH rECENT COLLECTION aCTIvITy was sOmEwHaT LEss INTENsIvE IN THE NOrTHErN rEGIONs (NOrTHErN SICHUaN, CHONGqING, HUbEI) THaN IN THE sOUTH, IT sEEms THaT THE arEa Of Dicharax fimbriatus Is rEsTrICTEd TO sOUTHErN prOvINCEs (wITH THE ExCEpTION Of a sINGLE LOCaLITy IN NOrTHErN SICHUaN).

Figures

FIGURE 33. Shells of Dicharax species. A – C. Dicharax diminutus (Heude, 1885). A. SMF 39255. B. Dicharax diminutus (lectotype of A. nanus Möllendorff, 1886, SMF 39246). C. 20060109 A, coll. PGB. D. Dicharax plicilabris (Möllendorff, 1886). Scale represents 5 mm. All photos: B. Páll-Gergely.