Metaxonchium silvaticum, 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 : 156-160

Metaxonchium silvaticum sp. n.

( FIgS 5 & 6 )

Material examined: TwElvE fEmAlES ANd ONE mAlE fROm CAT BA NATIONAl PARk, IN AccEPTAblE cONdITION. Morphometrics: SEE TAblE 1.

Description. Adult: MOdERATElY SlENdER NEmATOdES (a = 26–28) Of mEdIUm SIzE bOdY 1.27–1.48 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 STRONglY cURvEd vENTRAd UPON fIXATION, G– TO NEARlY O–SHAPEd. CUTIclE 1.0–1.5 µm THIck IN ANTERIOR REgION, 1.5–2.5 µm AT mId–bOdY ANd 6.5–8.5 µm ON dORSAl SIdE Of TAIl; IT IS 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, ANd THIck INNER lAYER, ESPEcIAllY ObvIOUS IN cAUdAl REgION. CERvIcAl lAcUNAE OfTEN clEARlY vISIblE. LATERAl cHORd vERY NARROw, 3.0–5.5 µm wIdE OR 6– 11% Of mId–bOdY dIAmETER, Of gRANUlAR NATURE ANd lAckINg ANY OTHER dIffERENTIATION. LIP REgION SOmEwHAT cAP– lIkE, OffSET bY wEAk dEPRESSION, 2.0–2.3 TImES AS bROAd AS HIgH OR UP TO ONE–SIXTH (14–16%) Of bOdY dIAmETER AT NEck bASE; lIPS PRObAblY PARTIAllY AmAlgAmATEd. AmPHId fOvEA cUP–lIkE, ITS APERTURE 6.0–6.5 µm wIdE OR OccUPYINg mOST (86–93%) lIP REgION dIAmETER. CHEIlOSTOm A TRUNcATE cONE, lAckINg ANY dIffERENTIATION. OdONTOSTYlE TYPIcAl Of THE gENUS, fUSIfORm, SHORT ANd STRONg, vISIblY lONgER (1.2–1.3 TImES) THAN lIP REgION dIAmETER, 3.4–4.5 TImES AS lONg AS wIdE ANd 0.62–0.70% Of bOdY lENgTH; APERTURE 2.5–3.5 µm lONg, OccUPYINg ONE–THIRd TO TwO–fIfTHS (20–42%) Of ITS lENgTH. GUIdINg RINg THIN, SImPlE bUT vISIblY REfRAcTIvE, AT 8–9 µm OR 1.1–1.3 TImES THE lIP REgION dIAmETER fROm THE ANTERIOR ENd. OdONTOPHORE ROd–lIkE 12–13 µm, 1.3–1.6 TImES THE OdONTOSTYlE lENgTH. 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 12–17 TImES AS lONg AS bROAd, 7.0–9.8 TImES lONgER THAN bOdY dIAmETER AT NEck bASE, ANd OccUPYINg 65–76% Of TOTAl NEck lENgTH; A vERY dISTINcT SPIRAl mUScUlAR SHEATH, wITH NEARlY STRAIgHT mUScUlAR bANdS, ENvElOPS THE wHOlE bASAl EXPANSION. CARdIA cONOId TO cONIcAl, 16–28 X 11 –16 µm wIdE, SURROUNdEd bY INTESTINAl TISSUE.

Female: GENITAl SYSTEm mONOdElPHIc–OPISTHOdElPHIc. ANTERIOR bRANcH REdUcEd TO A SImPlE UTERINE SAc 65–80 µm lONg, 1.0–1.6 TImES THE cORRESPONdINg bOdY dIAmETER ANd OccUPYINg 4–6% Of bOdY lENgTH. POSTERIOR bRANcH vERY vARIAblE IN lENgTH, 143–226 µm, OccUPYINg 11–17% Of bOdY lENgTH. OvARY REflEXEd, AlSO vERY vARIAblE IN lENgTH, 63–226 µm, wITH OOcYTES ARRANgEd fIRST IN SEvERAl ROwS ANd THEN IN A SINglE ROw. OvIdUcT jOININg THE OvARY SUbTERmINAllY, 54–66 µm lONg, 1.0–1.3 bOdY dIAmETERS, ANd cONSISTINg Of A TUbUlAR PART mAdE Of PRISmATIc cEllS ANd A PERcEPTIblE pars dilatata wITH vISIblE lUmEN. A dISTINcT NARROwINg SURROUNdEd bY A cONSPIcUOUS SPHINcTER SEPARATES OvIdUcT ANd UTERUS. UTERUS 77–80 µm lONg, 1.5–1.6 bOdY dIAmETERS OR 4–6% Of bOdY lENgTH, cONSISTINg Of A PROXImAl REgION wITH vISIblE lUmEN, AN INTERmEdIATE REgION wITH lESS cONSPIcUOUS lUmEN, ANd A SmAll, NEARlY SPHERIcAl, dISTAl pars dilatata. ONE fEmAlE bEARINg AN OvOId UTERINE Egg, 150 X 43 µm. VAgINA EXTENdINg INwARdS 21–25 µm, OccUPYINg lESS THAN ONE–HAlf (39–45%) Of THE cORRESPONdINg bOdY dIAmETER: pars proximalis 13.0–14.5 X 10–14 µm, wITH SOmEwHAT SIgmOId wAllS SURROUNdEd bY wEAklY dEvElOPEd cIRcUlAR mUScUlATURE; pars refringens (IN lATERAl vIEw) cONSISTINg Of TwO TRAPEzOIdAl PIEcES mEASURINg 2.5–3.5 X 5.0–5.5 µm ANd wITH A cOmbINEd wIdTH Of 11–13 µm; pars distalis cONSPIcUOUS, 5.5–7.0 µm lONg. VUlvA A SOmEwHAT POST-EqUATOIRAl TRANSvERSE SlIT. PREREcTUm 3.0–5.0, REcTUm 1.0–1.3 ANAl bOdY dIAmETERS lONg. CAUdAl REgION SHORT ANd ROUNdEd, REgUlARlY cONvEX, ANd bEARINg AbUNdANT blISTER– OR SAccATE bOdIES THAT ARE ESPEcIAllY dISTINcT AT ITS vENTRAl SIdE; cAUdAl PORES TwO PAIRS, ONE SUbdORSAl, ANOTHER lATERAl.

Male: GENITAl SYSTEm dIORcHIc, TESTES OPPOSEd. IN AddITION TO THE Ad–clOAcAl PAIR, SITUATEd AT 11 µm fROm clOAcAl APERTURE, THERE ARE SEvEN, SPAcEd (9–15 µm APART) vENTROmEdIAN SUPPlEmENTS, THE POSTERIORmOST Of wHIcH IS SITUATEd 22 µm fROm THE AdclOAcAl PAIR, NEARlY lEvEl wITH THE SPIcUlE ANTERIOR ENd. SPIcUlES dORYlAImOId, cURvEd vENTRAd, 5.1 TImES AS lONg AS wIdE ANd 1.6 TImES THE clOAcAl bOdY dIAmETER; HEAd 4.8 TImES AS lONg AS wIdE, OccUPYINg 29% Of SPIcUlE lENgTH ANd wITH ITS dORSAl SIdE vISIblY cURvEd ANd lONgER THAN THE vENTRAl ONE ; vENTRAl HUmP ANd HOllOw POORlY mARkEd, THE fORmER SITUATEd AT 51% Of SPIcUlE lENgTH; cURvATURE 130°; mEdIAN PIEcE OccUPYINg TwO–fIfTHS (40%) Of mAXImUm SPIcUlE wIdTH, REAcHINg THE SPIcUlE TERmINUS. LATERAl gUIdINg PIEcE 10.5 µm lONg, 5.2 TImES lONgER THAN bROAd, wITH SOmEwHAT fURcATE TERmINUS.

Diagnosis. Metaxonchium silvaticum SP. N IS cHARAcTERIzEd bY ITS 1.28–1.43 mm lONg bOdY, lIP REgION OffSET bY wEAk dEPRESSION ANd 7.0 µm bROAd, OdONTOSTYlE fUSIfORm ANd 8–9 µm lONg, NEck 5 02–630 µm lONg, bOTH PARTS Of THE PHARYNX SEPARATEd bY A SHORT ISTHmUS–lIkE NARROwINg, PHARYNgEAl EXPANSION 346–470 µm lONg ANd OccUPYINg 65–76% Of TOTAl NEck lENgTH, fEmAlE gENITAl SYSTEm mONO-OPISTHOdElPHIc, ANTERIOR gENITAl bRANcH REdUcEd TO A SImPlE UTERINE SAc 65–80 µm lONg, 1.0–1.6 TImES THE cORRESPONdINg bOdY dIAmETER, POSTERIOR UTERUS TRIPARTITE (bUT NOT EcHINOPHOR) ANd 77–80 µm OR 1.5–1.6 bOdY dIAmETERS lONg, V = 52–57, TAIl SHORT ANd ROUNdEd (18–23 µm, c = 56–74, c’ = 0.6–0.8) wITH AbUNdANT blISTER–lIkE OR SAccATE bOdIES, SPIcUlES 41 µm lONg, ANd SEvEN SPAcEd vENTROmEdIAN SUPPlEmENTS.

Relationships. THE NEw SPEcIES RESEmblES M. khainahillum ANd M. thornei . IT dIffERS fROm M. khainahillum IN ITS SmAllER gENERAl SIzE (bOdY lENgTH 1.28–1.43 vs 1.70–1.88 mm), lESS SlENdER bOdY (a = 26–29 vs a = 37–43), lONgER ANTERIOR UTERINE SAc (65–80 vs 16–38 µm, 1.0–1.6 vs lESS THAN 1.0 TImES THE cORRESPONdINg bOdY dIAmETER), SHORTER (18–25 vs 25–30 µm) fEmAlE cAUdAl REgION wITH (vs wITHOUT) SAccATE bOdIES, ANd PRESENcE (vs AbSENcE) Of mAlES. IT cAN bE dIffERENTIATEd fROm M. thornei bY ITS SmAllER gENERAl SIzE (bOdY lENgTH 1.28–1.43 vs 1.75–1.98 mm), wEAklY (vs dISTINcTlY) OffSET lIP REgION, ANTERIOR UTERINE SAc wITHOUT (vs wITH) A PROXImAl cONSTRIcTION, SHORTER (18–25 vs 30–33 µm, c’ = 0.6–0.8 vs c’ = 1.0–1.2) ANd mORE ROUNdEd (vs cONOId TO cONIcAl wITH ROUNdEd TIP) TAIl wITH (vs wITHOUT) SAccATE bOdIES, ANd fEwER (7 vs 13–15) SPAcEd (vs cONTIgUOUS) mAlE vENTROmEdIAN SUPPlEmENTS.

Type locality and habitat. NORTHERN VIETNAm, CAT BA NATIONAl PARk, HAI PHONg PROvINcE (GPS cOORdINATES: 20° 47'45'' N ANd 107° 00'40''E, ElEvATION 170 m), IN SOIl Of A TROPIcAl fOREST wHOSE dOmINANT PlANT SPEcIES IS Cinnamomum SP.

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

Etymology: THE SPEcIfIc EPITHET IS A LATIN TERm THAT mEANS bElONgINg TO THE fOREST ANd REfERS TO THE HAbITAT, A TROPIcAl fOREST, wHERE THE SPEcIES wAS cOllEcTEd.

Figures

FIGURE 5. Metaxonchium silvaticum sp. n. (Female). A: Female, entire. B: Anterior region in lateral median vieW. C: Pharyngo–intestinal junction. D: Vagina. E: Male, entire. F–H: Female, caudal region. I: Female, genital system, J: Female: posterior body region. K: Male, caudal region. L: Spicule and lateral guiding piece. (Scale bars: A, E = 200 µm; B, D = 5 µm; C, F–H, K, L = 10 µm; I= 50 µm; J = 20 µm.)

FIGURE 6.Metaxonchium silvaticum sp. n. (Female, LM). A: Female, entire.B: Anterior region in lateralmedian view. C: Pharyngo–intestinal junction. D: Uterus. E: Male, entire. F: Vagina. G, Q: Spicule. H: Sperm cells. I, J, L, M, N: Female, caudal region. K: Female, posterior body region. O, P: Male, caudal region and spicule. (Scale bars: A, E = 200 µm; B, F, H = 5 µm; C, G, I, J, L–Q = 10 µm; D, K = 20 µm.)