Encentrum essexis, Desmet, Willemh. & ARaYa, JEnnYM. SCHMId-, 2014

Desmet, Willemh. & ARaYa, JEnnYM. SCHMId-, 2014, Encentrum Essexis Sp. N. (Monogononta: Dicranophoridae), A New Rotifer Inhabiting Stream Benthos From East England, Acta Zoologica Academiae Scientiarum Hungaricae 60 (3), pp. 199-206 : 201-205

publication ID	https://doi.org/ 10.5281/zenodo.12626190
persistent identifier	https://treatment.plazi.org/id/03BF8405-FFA9-FFE1-284B-10D9FDFFFB7C
treatment provided by	Felipe
scientific name	Encentrum essexis
status	sp. nov.

Treatment

Encentrum essexis View in CoL sp. n.

(Figs 1–13)

Typelocality. BlackwaterRivercatchment (Kelvedon, Essex, EastAnglia, England, UK).

Holotype. Aparthenogeneticfemaleinapermanent, glycerineglassslidemountde- positedintheRoyalBelgianInstituteofNaturalSciences, ( R.B.I.N.), Brussels. Reg. N °. IG 32585 , RIR 213.

Paratypes. Oneslidewithparatype, andatrophipreparationmountedinFaure, in R.B.I.NReg. N°. IG 32585 , RIR 214. Threeotherslideswithparthenogeneticfemalesandtwo stubswithtrophipreparationsforSEMintheDepartmentofBiology, UniversityofAntwerp .

Diagnosis. Amedium- sized (± 170 μm) Encentrum . Coronaventral, small. Toesmoreorlessconicalindorsal/ventralview, withthreeelongatedropshapedlightrefractingbodiesleadingtotipoftoe (secretionreservoirs?); a weaklyindicatedtransversalfoldat 1/3 fromtip. Trophiof Isoencentrum - type, outlineofclosedramihexagonal. Innermarginofsubbasalramichambers withshorttooth. Intramalleiextendedtowardstrophiaxisintolongspiniform process. Eachramuswithtwolargepreuncinalteeth.

Etymology. Thespeciesname essexis isalatinizationofthetypelocality, Essex, asa nouninthegenitivecase.

Description. Parthenogeneticfemale. Body (Figs 1, 2) stout, fusiform, broadestatc. 1/3 fromanteriormarginindorsalview. Cuticlesmooth, notsticky. Headshort, c. 1/6 of totallength, veryslightlytiltedventrally, twotransversaldorso-lateralfoldsdistally; rostrumsmall, broadlyrounded; neckfoldapparentlyabsent; dorsalantennanearmiddleof head. Coronasmall, ventral. Trunkapparentlywithoutpseudosegments; inlateralview archeddorsally, highestinanteriorhalf, almoststraightventrallyorthenarrowerdistal partslightlydecurvedventrally; tailinconspicuous; lateralantennaeindistal 1/3 oftrunk. Footshort, withlargeproximal, andshortdistalpseudosegment. Toes (Figs 3–5) short, c. 1/18 oftotallength, withreservoirsindistalfootpseudosegment; moreorlessconicalin dorsal/ventralview, terminatingindistincttubuli; inlateralviewwithslightlydecurved dorsalmarginandweaklyindentedventralmargin; basesoftoessetclosetogether; each toewiththreeelongatedrop-like, light- refractingstructureswithtiny‘ canal’ leadingtotip (secretionreservoirs?).

Eyespot(s) apparentlyabsent. Brainfairlysmall, saccate; subcerebralglandspresent. Proventriculuspresent. Gastricglandsrounded, large, stalksmediumlong. Bladdernor- mal. Pedalglandsverylarge, extendingintotrunk, ovalinlateralview, indorsal/ventral viewwithobliqueproximalmargin, distalpartwithdistinctgranules; twosmallaccessory gland-likestructuresmedio-ventrally. Footdistallywithsinglemedio-dorsalsensorycell ofcaudalantenna. Vitellariumwith 8 nuclei.

Trophi (Figs 6–13). Ramioutlinehexagonal. Medianramiopeningbroadlywedge- shaped. Ramistout, eachwithaslender, offsetandincurvedapicaltooth; innermargin ofsubbasalramichamberswithshorttoothdistally; basifenestraesmall, subbasifenestrae large. Twopreuncinalteethofmorestrongerbuiltthanapicalramusteeth; outermargin oftheventralpreuncinalteethcontinuouswiththeramioutline, thedorsalonesplaced atarightangletothetrophiaxis; ventralpreuncinalteethwithcardalapophysis. Ful- crumslightlyshorterthanrami, narrowandparallel- sidedindorsal/ventralview, inlateral viewwithbroadbase, graduallytaperingdistally, slightlydecurvedventrally. Uncisingle- toothed, toothslightlyshorterthanshaft, expandedinthedorso-ventralplane; dorsalapophyseswelldeveloped; shaftsdistallywithdistinctdorsalexpansion. Intramallei ( Fig. 13 View Figs 7–13 ) moreorlesstrapezoidinlateralview; anteriormarginwithtwobroadandfairlyshallow apophyses; medialmarginventrallywithdistalpartextendedintolongspiniformprocess pointingtothetrophiaxis. Supramanubrianarrow, tipsrecurvedrostrally. Manubriaincurvedinthreeweaksteps; caudawithsmallcrutch; headwithtriangularexpansionand opening.

Male unknown.

Measurements. Length (N = 5) 162–183 μm (mean = 171 μm), toe 9–13 μm (mean = 11 μm); trophi (N = 3) 23–24 μm, ramus 8.5–10 μm, fulcrum 6.5–8 μm, uncus 8–9 μm, intramalleus 4–6 × 2 μm, supramanubrium 5–5.5 μm, manubrium 16–18 μm.

Figs 1–6. Encentrumessexis sp. n.: 1 = female, ventralview, 2 = female, lateralview, 3 = toes, dorsalview, 4–5 = toes, lateralview, 6 = trophi, dorsalview.Scalebars: 1, 2: 50 μm; 3–6: 10 μm.

Comments. Onthebasisofthemorphologyofthetrophi, e.g. thepres- enceofsupramanubria, theposteriortaperingandventrallydecurvedful- crum, andtheshapeoftheramioutline, thenewspeciesbelongstothesubge- nus Isoencentrum De Smet, 1997 .

The trophi of E. essexis sp. n. remind its congeners E. frenoti De Smet, 2002 , E. graingeri Chengalath, 1985 , E. spinosum Koch- Althaus, 1962 and E. tobyhannaensis Myers, 1940 , whichshowatoothonthesub-basalramicham- berslikewise. Ofthese, E. frenoti and E. graingeri aremarineelements, and theothersinhabitfreshwaters. Encentrumessexis sp. n. sharesthecharacter twopairsofpre- uncinalteethwith E. graingeri , butdiffersbythehexagonal ramioutline (circularin E. graingeri ), andtheuncinalteethwhichareslightly shorterthantheshaft (shaft- lengthin E. graingeri ). Theotherspeciesdisplay asinglepairofpreuncinalteeth (however, notconfirmedbySEMfor E. spinosum and E. tobyhannaensis ), and show an obpyriform ( E. frenoti , E. spinosum ) or heart- shaped ( E. tobyhannaensis ) ramioutline. Apronouncedlongspiniform processonthemedialintramalleusmarginisonlypresentinthenewspecies. Furthermajordifferencesarefoundinanatomicalandexternalmorphologi- calfeatures. Thethreelight- refractingbodiesineachtoearepresentinthe newspeciesonly. Themostobviousdifferencesto E. frenoti arethelackof S-shapedglandularappendagesconnectedtothebrain, thenormalbladder (longin E. frenoti ), andthecontinuousoutlineofthetoes (toesabruptlyoffset nearmid-lengthin E. frenoti ). Encentrumessexis sp. n. differsfrom E. graingeri byitsmorerobusttoes, theventralcorona (obliquein E. graingeri ), andthe medium- longstalksofthegastricglands (long-stalkedin E. graingeri ).

Thenewspeciesdiffersfrom E. spinosum bytheabsenceoflongitudinal foldsintheanteriorhalfofthetrunk. Encentrumessexis sp. n. isdistinctfrom E. tobyhannaensis byitsconicaltoes (parallel- sidedinthelatter), andtheabsenceofalongretrocerebralsacandzoochlorellaeinthestomachwall, and thepresenceofgastricglands.

Distributionandecology. Todate, E. essexis sp. n. isonlyknownfrom itstypelocality: theBlackwaterRivernearKelvedon (51°50’0”N, 0°43’0”E) in Essex, UK. The specimens of E. essexis were found in only one of 25 benthic samples. Inthesamearea, therewasadiverseprotozoanandinvertebrate assemblagesincluding 34 testatespecies, 20 speciesofchironomids, 7 oligochaeteand 21 rotiferspecies. ThemostabundanttaxainFebruary 2000 were testateamoebae (76%), followedbyciliates (12%) androtifers (7%) (SCHMId & SCHMId- ARaYaunpubl.). Amongrotifers, themostabundantspecieswere Philodina flaviceps Bryce, 1906 (10%), Encentrum spp. (59%), and Colurella adriatica Ehrenberg, 1831 (6%) co-occurringwiththenew Encentrum species.

Furtherupstreaminthesamecatchment, REIssandSCHMId- ARaYa (2008) foundverydiverseciliateandmeiofaunalassemblagescomposedof 32 spe- ciesofciliates, 52 speciesofrotifersandafurther 35 speciesbelongingtoi.e. oligochaetes, copepods, gastrotrichsandnematodes. Therotiferswerevery abundantinthePantstreamandaccountedformorethan 80% ofthetotal meiofaunalabundanceinspring, buttheydidnotcontributesubstantiallyto biomassandsecondaryproduction (REIss & SCHMId- ARaYa 2008). Themost abundantamongtherotiferswere Proalesfallaciosa Wulfert, 1937 (27%), Notholca squamula (Müller, 1786) (23.6%), Resticula sp. (6.7%), and Cephalodella spp. (6.7%) (REIsspers. comm.). Thegenuswithmostspecieswas Cephalodella ( C. cf. euderbyi Wulfert, 1940 , C. gibba (Ehrenberg, 1830) , C. globata (Gosse, 1887) , C. cf. intuta Myers, 1927 , C. megalocephala (Glascott, 1893) , C. pachyodon Wulfert, 1937 , C. ventripes (Dixon-Nutall, 1901) andseveraltypesof Cephalodella spp. ), followed by Encentrum ( E. cf. uncinatum (Milne, 1886) , E. putorius Wulfert, 1936 , E. cf. eurycephalum Wulfert, 1936 , E. incisum Wulfert, 1936 , and Encentrum spp. ), Dicranophorus ( D. forcipatus (Müller, 1786) , and Dicranophorus spp. ) and the bdelloid Philodina ( P. acuticornis Murray, 1902 , P. citrina Ehrenberg, 1832 , P. flaviceps and Philodina spp. ). This largely agrees with former observationsthatthreefamilies, Dicranophoridae , NotommatidaeandPhilodi- nidae, accountformostoftheabout 150 rotiferspeciesreportedfrombenthos ofloticenvironments (SCHMId- ARaYa 1998 b, WaLLaCE etal. 2006).

Thegenus Encentrum View in CoL isomnivorous, comprisingspeciesfeedingonde- tritusandassociatedbacteria, unicellularalgae, diatoms, testateamoebae, euglenoids, ciliates, nematodes, rotifers, etc. ( DESMET 1997). Somespecies feedequallyondifferentfooditems, e.g. diatomsandotherrotiferspecies (SCHMId- ARaYa & SCHMId 1995). Examinationofthegutcontentsof E. essexis sp. n. revealsthatitselectivelyfeedsondiatoms, suchas Naviculalanceolata (Agardh) Ehrenberg, 1838.

Acknowledgements – TheLaboratoryofCellBiologyandHistology, UniversityofAnt- werp, providedthenecessarySEMfacilities. Dr. B. VanDeVijverkindlyidentifiedthedia- toms. JSAisgratefultostudentsfromtheDiversityofLifemodule (2009–2011) atQMUL forconstantmotivation.