Polycelis yangchengensis, Dong, Chen, Zhang & Liu, 2017

Dong, Zi-Mei, Chen, Guang-Wen, Zhang, He-Cai & Liu, De-Zeng, 2017, A New Species Of Polycelis (Platyhelminthes, Tricladida, Planariidae) From China, Acta Zoologica Academiae Scientiarum Hungaricae 63 (3), pp. 263-276 : 264-270

Polycelis yangchengensis sp. n.

(Figs 1–8)

Materialexamined – Holotype: CQ1,onesetofsagittalsectionson 5 slides,Cheng- qianggenofTaihangMountainsinYangchengCounty, ShanxiProvince, 05 July 2002, alt. 1658 mat 112°09.133 ′ E, 35°16.398 ′ N; watertemperature 5.5–10.5°C, pH 6.0.

Paratypes: CQ2, ChengqianggenofTaihangMountainsinYangchengCounty, Shanxi Province, 05 July 2002, sagittalsectionson 8 slides; CQ3–4, ibid, transversesectionson 9, and 10 slides, respectively; CQ5–6, ibid, horizontalsectionson 6, and 8 slidesrespectively .

Othermaterial : RB1–2,RenbiRutofTaihangMountainsinYangchengCounty, Shanxi Province, 06 July 2002, alt. 1371 mat 112°08.424 ′ E, 35°16.251 ′ N; watertemperature 5.5–10.5°C, pH 6.0, sagittalsectionson 9, and 8 slides; RB3, 4, 5, ibid, horizontalsectionson 6, 8, and 9 slidesrespectively; RB6–7, ibid, transversesectionson 15, and 10 slidesrespectively .

Diagnosis – Prepharyngealtestes, fillingmostofthedorso- ventralspace extendingfromtheleveloftheovaries. Penisalongconewithwell-developed musculature.Boundarybetweenpenisbulbandpenispapillavague.Bulbar cavitynotobserved.Twospermductsenteringtotheejaculatoryductsepa- ratelyatthe 1/3rd–1/4thaslongasthepenisnearthedistalportion. Bursal canalwithaninnerwell-developedcoatofcircularmusclesandathinouter longitudinalone. Chromosomecomplementconsistingofadiploidnumber of 38 chromosomes, withkaryotypeformula 2n = 38 = 24m + 14sm.

Etymology – Thisspeciesisnamedafterthegeographiclocation (Yangchengcounty)

whereitstypespecimenwasfound.

Externalcharacters – Thegeneralappearanceofthelivingspecimensofthisspecies isshowninFigs 1A, B. Thelivingsexuallymatureindividualsmeasureupto 12–17mm inlengthand 1.5–2.5 mminwidth. Inlife, theheadhasabroad, subtriangularformand frontalbodymarginprovidedwithamedianbulge, withapairofratherpointedauricles extendinganterolaterally. Posteriorlytotheauricles, thebodyisslightlynarrowerand thengraduallywidensagain. Afterthis, thebodyremainsaboutthesamewidthuntilthe

regionofthecopulatorycomplex. Posteri-

orlytothecopulatorycomplex, thebody

graduallybecomesnarrowertoendina

blunt tail (Figs 1A, B).

Thecoloroflivingspecimensistawny

todarkchocolate- brownofthedorsalside,

while, theventralsideisslightlylighterthan

thatofthedorsalbodysurface. Thecolorof

fixedspecimensisgraywhite. Inlivingfully

sexuallymaturespecimens, thecopulatory

bursa, thepenisandapartofspermiducal

vesiclecanbeseenfromtheventralside

(Figs 1A, B).

Thespeciespossessesnumerous

smalleyesarrangedintwobands (80–140

intotal) neartheanteriorandthelateral

marginsofthehead. Therearenoeyesin

themid- dorsalpartofthehead. Theseocu-

larbandsarewidestattheleveloftheau-

riclesandterminatesomedistancebehind

theauriclesattheanteriorone- fifthlevel Fig. 1. Photographsof Polycelisyangchengen- oftheprepharyngealregion. Withineach sis, livespecimens: A = sexuallyimmaturein- bandthesmalleyesaredistributedirregu- dividual, B = sexuallymatureindividuallarly (Figs 1A, B).

Thepharynxisinsertedintheposteriorhalfofthebody. Itislongandstrongly musculaturewithalengthnearly 1/3–1/4thaslongasthebodylengthandwithawidthof nearly 1/3rdofthebodywidth. Themouthislocatedatthehindendofthemiddle 1/4th ofthebody. Thegenitalporeisfoundinthemidlineatratherposteriorlevelofthemiddle ofthepostpharyngealregion, theratioofthedistancesbetweenmouthtogonoporeand genitalporetotheendofthetailis 4:3 (Figs 1A, B).

Internalcharacters – Thepharynxhasastructuretypicalofthegenus Polycelis inthe familyPlanariidae, themusculatureofthepharynxconsistsoftwolayers: outerepithelium ofpharynxunderlainbyalayeroflongitudinalmuscles, followedbylayerofcircularmuscles. Athicklayerofcircularmuscleunderinnerpharynxepitheliumisfollowedbyathin layeroflongitudinalmusclefibers.

Theanteriorintestinaltrunkhas 6–10 pairsoframus; eachoftheposteriortrunks shows 12–16 ramus.

Thenumeroustestesarewell-developed, large, andovalinshape. Fullysexuallyma- tureindividualshave 50–60 testesintotal, distributedintotwolongitudinalbands, oneon eachsideoftheanteriorintestinaltrunk (Fig. 2C).Thetestesextendfromthelevelofthe ovariestotherootofthepharynx (Figs 2C, 4A, B). Mosttestesfillalmostcompletelythe dorso- ventralspace (Figs 2A, B). Thetwospermductsenlargetoformspermiducalvesicles oneithersideoftheposteriorpartofthepharynx, whichdecreaseindiameterbeforepen- etratingtheproximal, anterolateralwallofthepenis ( Fig. 3A). Withinthepenis, thesperm ductsrunseparatelyforaconsiderabledistance, andthenenterintotheejaculatoryduct respectivelyonlyatthe 1/3rd–1/4thaslongasthepenisnearthedistalportion ( Figs 3B–F).

Apairofmoderatelysizedovariesissituatedintheusualventralspacejustbehind thebrainandbetweenthesecondandthirddiverticulaoftheanteriorintestinaltrunk; it Fig. 2. Photomicrographsshowingthetestesindifferentsectionsof Polycelisyangchengensis: A = specimenRB7-2, transversesection, B = specimenRB2-5, sagittalsection, AandB showingthetestesfillingthedorso- ventralspace, C = specimenRB4-3, horizontalsection

showingthetestesextendingtotherootofthepharynx

thetwospermductsandejaculatory

posteriorpart (thepositionofthepenispapilla) hastheshapeofanelongatedcone, and itsdorso- ventrallipissymmetrical, theejaculatoryductisratherwideandopensattipof penis (Figs 5, 6A–C). Themusculatureofthepenisiswell-developed, consistingofavery thicklayerofinnercircularfibersandathinlayerofouterlongitudinalone (Figs 5, 6D).

Karyology – Weexamined 100 well-dispersedmetaphaseplatesof Polycelisyangchengensis.In 69.82. % ofthemetaphaseplatesthechromosomenumberwas 2n = 38. Karyotype parameters, includingtherelativelength, armratio, andcentromereindex, aregiveninTa- ble 1. AchromosomalplateandtheidiogramofthekaryotypeareshowninFigs 7A, Band C. Theresultsindicatethatthekaryotypeof Polycelisyangchengensis showsadiploidnumberof 38, withakaryotypeformulaof 2n = 38 = 24m + 14sm, inwhichNos 6, 9, 10, 13, 14, 16 and 19 aresubmetacentricandtheothersaremetacentric. Thefirstpairofchromosomes isclearlylargerthantheotherpairsbeing 5.37 timesaslargeasthesmallestchromosome.

Distributionandecology – Thisspeciesisdistributedabovealt. 1100 m andshowstheobviousverticaldistribution (Figs 8A, B). Theywerefound togetherwith Dugesia speciesataboutalt. 1000 m, the Dugesia speciesaredistributedbelowalt. 1000 minthesamemountain. Uptothepresent, wehave notobservedfreshlyregeneratedanteriororposteriorendsbothinthelocality andthelaboratoryculture, so, wepresumethatthisspeciesreproducesonly sexually. Itsbreedingseasonisusuallyfromautumntothenextspring (Octo- bertoFebruaryofnextyear). Thenewlylaidcocoonsarered- brown (Fig. 8C), andthenturnbrownishdarkafter 2 to 3 days, theyhatchabout 70–110 days

Fig. 5. Polycelisyangchengensis: HolotypeCQ1, sagittalreconstructionofthecopulatoryapparatus (anteriortotheright)

afterlayingat 4°Cinthelaboratoryand 50–80 daysinthefieldlocations, 4 to 6 juvenilesemergefromonecocoonandtheyare 3–5 mmlongand 0.6–1.0 mm wide. Thecocoonissphericalinshape (2–2.5 mmindiameter) andwithout astalk, thenewjuvenileplanariansarewhiteandtranslucent, theyattainthe colorofmaturespecimensinthecourseofthefirstmonth (Fig. 8C).