Metaxonchium bonkowskii, Nguyen & Peña-Santiago, 2018

Nguyen, Thi Anh Duong & Peña-Santiago, Reyes, 2018, Two new species of the genus Metaxonchium Coomans & Nair, 1975 (Nematoda, Dorylaimida, Belondiridae) from Vietnam, Zootaxa 4415 (1), pp. 150-160 : 151-156

Metaxonchium bonkowskii sp. n.

( FIgS 1–4 )

Material examined: TwENTY fOUR fEmAlES fROm HUU LIEN NATURAl RESERvE, IN vERY gOOd cONdITION.

Morphometrics: SEE TAblE 1.

Description. Female: MOdERATElY SlENdER TO SlENdER (a = 27–32) NEmATOdES Of mEdIUm SIzE, 1.69–2.23 mm lONg. BOdY cYlINdRIcAl, vISIblY TAPERINg TOwARdS THE ANTERIOR ENd, lESS SO TOwARdS THE POSTERIOR ENd SINcE THE cAUdAl REgION IS SHORT ANd ROUNdEd. HAbITUS cURvEd vENTRAd UPON fIXATION, C– TO O– SHAPEd. CUTIclE 2.0–2.5 µm THIck IN ANTERIOR REgION, 2.5–4.0 µm AT mId–bOdY ANd 10–12 µm ON dORSAl SIdE Of TAIl; TwO–lAYEREd, cONSISTINg Of OUTER lAYER dISTINcTlY THINNER THAN THE INNER ONE, wITH cONSTANT THIckNESS THROUgHOUT THE bOdY, APPARENTlY dIvIdEd IN TwO SUblAYERS, ANd bEARINg vERY fINE TRANSvERSE STRIATION ONlY dISTINcTlY PERcEPTIblE wITH SEM, ANd THIck INNER lAYER, ESPEcIAllY ObvIOUS AT cAUdAl REgION wHERE IT dISPlAYS dISTINcT RAdIAl STRIATION. LATERAl cHORd vERY NARROw, 3.5–6.0 µm bROAd, lESS THAN ONE TENTH (5–9%) Of mId–bOdY dIAmETER, gRANUlAR IN APPEARANcE, wITH vERY SmAll OvOId glANd bOdIES. LIP REgION SlIgHTlY cAP–lIkE, OffSET bY wEAk bUT PERcEPTIblE cONSTRIcTION, 2.6–2.9 TImES AS bROAd AS HIgH ANd UP TO ONE–fIfTH (13–20%) Of bOdY dIAmETER AT NEck bASE. IN OUR SEM ObSERvATIONS, THE lIPS ARE SEPARATEd bY RAdIAl (lONgITUdINAl) INcISURES; IN THE cASE Of THE TwO SUbdORSAl ANd THE TwO SUbvENTRAl ONES, THESE dO NOT REAcH THE lIP REgION bASE; lATERAl lIPS APPARENTlY SmAllER THAN THE OTHERS (THE AvAIlAblE PIcTURES dO NOT AllOw cONfIRmATION Of THIS POINT), SO THAT THE lIP REgION SHOwS A bIRAdIAl SYmmETRY; lAbIAl PAPIllAE vERY dISTINcT, wEAklY PROTRUdINg, cONSISTINg Of A cENTRAl PORE SURROUNdEd bY A cIRcUlAR INcISURE; cEPHAlIc PAPIllAE, vERY lOw, REdUcEd TO A SImPlE PORE NOT SURROUNdEd bY ANY INcISURE; ORAl APERTURE SOmEwHAT HEXAgONAl; ORAl fIEld SmAll SINcE THE INNER lAbIAl PAPIllAE ARE SITUATEd clOSE THE ORAl APERTURE. AmPHId fOvEA cUP–lIkE, ITS APERTURE 8.5–9.5 µm bROAd, OccUPYINg NEARlY THE ENTIRE (81–95%) lIP REgION dIAmETER. CHEIlOSTOm A TRUNcATE cONE, lAckINg ANY dIffERENTIATION. OdONTOSTYlE TYPIcAl Of THE gENUS, fUSIfORm, SHORT ANd STRONg, ONlY SlIgHTlY lONgER (1.1–1.3 TImES) THAN lIP REgION dIAmETER, 4.0–4.8 TImES AS lONg AS wIdE ANd 0.59–0.67% Of bOdY lENgTH; APERTURE 3.0–4.0 µm lONg, OccUPYINg ONE–fOURTH TO ONE–THIRd (24– 33%) Of OdONTOSTYlE lENgTH. GUIdINg RINg THIN, SImPlE bUT vISIblY REfRAcTIvE, AT 11.0–12.0 µm OR 1.1–1.2 TImES THE lIP REgION dIAmETER fROm THE ANTERIOR ENd. OdONTOPHORE ROd–lIkE 16.5–17.5 µm, 1.1–1.2 TImES THE OdONTOSTYlE lENgTH, bEARINg A vERY SlIgHT THIckENINg AT ITS APPROXImATE mIdPOINT. PHARYNX cONSISTINg Of A SlENdER ANd wEAklY mUScUlAR ANTERIOR PORTION SEPARATEd fROm THE bASAl EXPANSION bY A SHORT ISTHmUS–lIkE SEcTION, ANd A bASAl EXPANSION 10–18 TImES AS lONg AS bROAd, 6.0–9.0 TImES lONgER THAN bOdY dIAmETER AT NEck bASE, ANd OccUPYINg 67– 77% Of TOTAl NEck lENgTH; A vERY dISTINcT SPIRAl mUScUlAR SHEATH, wITH NEARlY STRAIgHT mUScUlAR bANdS, ENvElOPS THE wHOlE bASAl EXPANSION. CARdIA cONOId TO cONIcAl, 27– 45 X 17–24 µm wIdE, SURROUNdEd bY INTESTINAl TISSUE. GENITAl SYSTEm mONOdElPHIc–OPISTHOdElPHIc. ANTERIOR gENITAl bRANcH REdUcEd TO A UTERINE SAc 75–135 µm lONg, 1.1–1.9 TImES THE bOdY dIAmETER OR 4–7% Of bOdY lENgTH, OccASIONAllY cONTAININg SPERm cEllS, ANd wITHOUT ANY RUdImENTS Of OvIdUcT OR OvARY. POSTERIOR bRANcH wEll dEvElOPEd, 200–293 µm OR 11–15% Of TOTAl bOdY lENgTH; -THESE vAlUES, HOwEvER, SHOUld bE TAkEN wITH cAUTION SINcE THE gENITAl TRAcT vERY OfTEN bEcOmES EXTREmElY cONvOlUTEd— REflEXEd OvARY vARIAblE IN lENgTH, 70–157 µm, wITH OOcYTES ARRANgEd fIRST IN SEvERAl ROwS ANd THEN IN A SINglE ROw; OvIdUcT jOININg THE OvARY SUbTERmINAllY, 83–113 µm lONg OR 1.4–1.6 bOdY dIAmETERS lONg, ANd cONSISTINg Of A TUbUlAR PART cOmPOSEd Of PRISmATIc cEllS ANd A wEll dEvElOPEd pars dilatata wITH dISTINcT lUmEN; A

mARkEd NARROwINg wITH ASSOcIATEd SPHINcTER SEPARATES OvIdUcT ANd UTERUS; UTERUS 108–187 µm lONg ANd TETRAPARTITE, i.e., wITH bROAd PROXImAl REgION wITH vISIblE lUmEN, A NARROwER INTERmEdIATE REgION wITH NARROw TO ImPERcEPTIblE lUmEN, A SHORT bUT dIlATEd REgION cONTAININg AbUNdANT REfRAcTIvE gRANUlAR bOdIES (Z ORgAN), ANd A SPHERIcAl dISTAl PART, AlSO wITH vISIblE lUmEN; UTERINE Egg OvOId, 132–149 X 43 –58 µm. VAgINA EXTENdINg INwARdS 28–34 µm lONg, OccUPYINg TwO–fIfTHS TO ONE–HAlf (40–52%) Of THE cORRESPONdINg bOdY dIAmETER: pars proximalis 16– 22 X 12–15 µm, wITH NEARlY STRAIgHT wAllS ANd SURROUNdEd bY mOdERATElY dEvElOPEd, cIRcUlAR mUScUlATURE; pars refringens cONSISTINg (IN lATERAl vIEw) Of TwO TRAPEzOIdAl PIEcES 5.5–6.5 X 6.0–7.0 µm ANd wITH A cOmbINEd wIdTH Of 12–16 µm; pars distalis cONSPIcUOUS, 5.5–6.5 µm lONg. VUlvA A TRANSvERSE, AbOUT 12 µm lONg SlIT. PREREcTUm 2.6–4.9, REcTUm 1.0–1.2 ANAl bOdY dIAmETERS lONg. ANUS A TRANSvERSE, AbOUT 8 µm lONg SlIT, wITH SlIgHTlY PROTRUdINg ANTERIOR lIP. CAUdAl REgION SHORT ANd ROUNdEd, NEARlY HEmISPHEROId; cAUdAl PORES TwO PAIRS AT THE POSTERIOR HAlf Of TAIl, ONE lATERAl, ANOTHER SUbdORSAl.

Male: NOT fOUNd bUT PRESUmAblY EXISTINg AS A fEw fEmAlES cONTAIN SPERm cEllS IN THEIR gENITAl TRAcT.

Diagnosis. Metaxonchium bonkowskii sp. n. IS cHARAcTERIzEd bY ITS 1.69–2.23 mm lONg bOdY, lIP REgION OffSET bY cONSTRIcTION ANd 9.5–10.5 µm bROAd, OdONTOSTYlE 11–12 µm lONg ON vENTRAl SIdE ANd 12–13 µm lONg ON dORSAl SIdE, NEck 673–868 µm lONg wITH PHARYNgEAl EXPANSION 461–649 µm lONg OR OccUPYINg 66–77% Of TOTAl NEck lENgTH, fEmAlE gENITAl SYSTEm mONO–OPISTHOdElPHIc, ANTERIOR gENITAl bRANcH REdUcEd TO UTERINE SAc 75–135 µm lONg OR 4–7% Of bOdY lENgTH, POSTERIOR UTERUS TETRAPARTITE ANd INclUdINg A Z–lIkE dIffERENTIATION, V = 51–55, ANd fEmAlE TAIl SHORT ANd ROUNdEd (20–27 µm, c = 68–97, c’ = 0.5–0.7).

Relationships. THE NEw SPEcIES RESEmblES M. japonicum ( AHmAd & NAz, 2010) PEñA-SANTIAgO, NIkNAm, ÁlvAREz-ORTEgA & JAbbARI, 2014, M. mizukuboi ( AHmAd & NAz, 2010) PEñA-SANTIAgO, NIkNAm, ÁlvAREz-ORTEgA & JAbbARI, 2014 ANd M. thornei ( HEcHlER, 1969) ANdRáSSY, 1996. IT cAN bE EASIlY dISTINgUISHEd fROm THESE THREE SPEcIES bY ITS lESS SlENdER bOdY (a = 22–32 vs a = 36–39, 46–52 ANd 33–42, RESPEcTIvElY), SHORTER (1.1–1.9 vs 3.3– 4.1, 2.7–3.2 ANd 2.0–2.7 TImES THE bOdY dIAmETER, RESPEcTIvElY) fEmAlE ANTERIOR gENITAl bRANcH, ANd, mOST ImPORTANTlY, TETRAPARTITE (vs TRIPARTITE) UTERUS wITH (vs wITHOUT) Z–lIkE dIffERENTIATION. IT AlSO dIffERS fROm M. japonicum ANd M. mizukuboi IN ITS cOmPARATIvElY SmAllER SIzE (bOdY lENgTH 1.69–2.23 vs 2.3–2.4 mm), ANd, mOREOvER, IT cAN bE SEPARATEd fROm M. mizukuboi bY AbSENcE (vs PRESENcE) Of A RUdImENTARY mASS (OvIdUcT/OvARY) AT THE TIP Of THE fEmAlE ANTERIOR gENITAl bRANcH. IT dIffERS fROm M. thornei IN HAvINg THE fEmAlE ANTERIOR gENITAl bRANcH wITHOUT (vs wITH) A PROXImAl cONSTRIcTION, ANd mORE ROUNdEd (NEARlY HEmISPHEROId vs PERcEPTIblY cONOId) ANd RElATIvElY SHORTER (20–27 µm, c = 68–97, c’ = 0.5–0.7 vs 30–36 µm, c = 52–66, c’ = 1.0–1.2) fEmAlE TAIl.

Metaxonchium bonkowskii sp. n. AlSO RESEmblES M. khainahillum ( GAmbHIR & DHANAcHANd, 1991) ANdRáSSY, 1996, M. spiculum ( AHmAd & JAIRAjPURI, 1982) ANdRáSSY, 1996 ANd M. tacitum ( AHmAd & JAIRAjPURI, 1982) ANdRáSSY, 1996 IN ITS gENERAl mORPHOlOgY. IT SHOUld bE NOTEd THAT THESE THREE SPEcIES ARE ATYPIcAl wITHIN THE gENUS (cf. PEñA–SANTIAgO et al., 2014) dUE TO AbSENcE Of AN ISTHmUS–lIkE NARROwINg SEPARATINg bOTH PHARYNgEAl SEcTIONS, wHIcH APPEAR AbUTTINg ANd wITH A dEEP cONSTRIcTION bETwEEN THEm. THE NEw SPEcIES, HOwEvER, dISPlAYS A SHORT ISTHmUS–lIkE NARROwINg bETwEEN THE PHARYNgEAl SEcTIONS. MOREOvER, THE THREE SPEcIES lAck A UTERINE Z–lIkE dIffERENTIATION.

Type locality and habitat. NORTHERN VIETNAm, HUU LIEN NATURAl RESERvE, LANg SON PROvINcE, (GPS cOORdINATES: 21° 42'51'' N ANd 106° 21'48''E, ElEvATION 502 m), IN SOIl Of NATIvE fOREST wHOSE dOmINANT PlANT SPEcIES ARE Machilus SP. ANd Dimocarpus SP.

Type material. FEmAlE HOlOTYPE ANd TEN fEmAlE PARATYPES dEPOSITEd wITH THE NEmATOdE cOllEcTION Of THE UNIvERSITY Of JAéN, SPAIN. TwElvE fEmAlE PARATYPES wITH NEmATOdE cOllEcTION Of THE INSTITUTE Of EcOlOgY ANd BIOlOgIcAl RESOURcES ( IEBR), HANOI, VIETNAm.

Etymology: THE NEw SPEcIES IS NAmEd AfTER PROf. MIcHAEl BONkOwSkI (UNIvERSITY Of COlOgNE, GERmANY) fOR HIS SUPPORT TO THE fIRST AUTHOR dURINg HER STAY IN GERmANY.

Remarks. THE NEw SPEcIES IS RATHER UNUSUAl wITHIN THE gENUS IN HAvINg A Z–lIkE dIffERENTIATION, cONSISTINg Of AbUNdANT REfRINgENT gRANUlES cONcENTRATEd IN A RElATIvElY SHORT SEcTION Of THE UTERUS clOSE TO THE dISTAl pars dilatata. A TOTAl Of SEvEN Metaxonchium SPEcIES (PEñA-SANTIAgO et al., 2014) SHOw AbUNdANT SclEROTIzEd APOPHYSES THROUgHOUT THE NARROwER, INTERmEdIATE SEcTION Of THE UTERUS, THE EcHINOPHOR UTERUS sensu ANdRáSSY (1996), bUT THIS TYPE Of dIffERENTIATION IS NOT TOTAllY cOmPARAblE wITH THAT HEREIN ObSERvEd.

Figures

FIGURE 1. Metaxonchium bonkowskii sp. n. (Female). A: Entire. B: Anterior region in lateral, median vieW. C: Anterior region in lateral surface vieW.D: Genital system. E: Pharyngeal enlargement.F: Posterior body region.G: Pharyngo–intestinal junction.H: Vagina.I: Caudal region.J: Oviduct–uterus junction. (Scale bars:A = 200 µm; B, C = 5 µm; D= 50 µm; E, H, I = 10 µm; F, G, J = 20 µm.)

FIGURE 2. Metaxonchium bonkowskii sp. n. (Female, LM). A, B, F: Entire.C, D, H: Anterior region in lateral, median vieW. E, I: Anterior region in lateral surface vieW. F: Genital system. G: Posterior body region. H: Vagina and uterine egg. I–K: Caudal region.L: Vagina. (Scale bars: A, B, F = 200 µm; C, D, E, H, I = 5 µm; G, L–N = 10 µm; G, J, K = 20 µm.)

FIGURE 3. Metaxonchium bonkowskii sp. n. (Female, LM). A, D: Genital system. B: Anteior uterine sac. C: Uterine egg. E, G, K: Oviduct–uterus junction, shoWing (arroWs) the Z–organ. F, H: Vagina. I: Sperm cells. J: Detail of Z–organ granules. (Scale bars: A, C, D, G = 50 µm; B, E = 20 µm; F, K = 10 µm; H–J = 5µm.)

FIGURE 4. Metaxonchium bonkowskii sp. n. (Female, SEM). A: Lip region in sublateral vieW. B: Same in face vieW. C: Caudal region in lateral vieW.D: Same in ventral vieW.E: Vagina in ventral vieW.(Scale bars: A, B = 2 µm; C–E = 4 µm.)