Mononchus truncatus Bastian, 1865

Andrássy, István, 2011, Three new species of the genus Mononchus (Nematoda: Mononchida), and the “ real ” Mononchus truncatus Bastian, 1865, Journal of Natural History 45 (5 - 6), pp. 303-326 : 317-326

Mononchus truncatus Bastian, 1865

( Figures 8A–E and 9A–J )

Females (n = 22): L = 1.72–2.12 mm; a = 27–35; b = 3.8–4.3; c = 7.5–8.4; c’ = 6.3–7.6; V = 52–56%.

Male: L = 1.80 mm; a = 38; b = 3.9; c = 10.8; c’ = 3.7.

General characters

A medium-sized species, close to 2 mm, but usually shorter. Body hardly bent after fixation, 38–40 µm wide at posterior end of buccal cavity, 60–62 µm wide at cardia and 62–74 µm wide at mid-body region. Cuticle practically smooth and thin, 2.0–2.5 µm on most of body. Lip region narrow, not offset, 24–25 µm wide at lateral lips. Lips amalgamated. Body at proximal end of pharynx 2.1–2.6 times as wide as labial region. Oral field slightly protruded, 2–3 µm high. Amphids small, their aperture levelling to the entrance of buccal capsule.

Distance between the oral field and beginning of buccal capsule 8–9 µm long. Buccal capsule large, 41–46 µm long, occupying 9–10% of pharyngeal length, 18–21 µm wide at anterior third and 16–18 µm wide at posterior third, 2.2–2.5 / 2.3– 2.8 times as long as wide, or 1.7–1.8 times as long as lip region width. Dorsal tooth strong, 4–6 µm long from base to apex, its apex lying 10–12 µm from beginning of buccal capsule, or at 25–29% of buccal length. Transversal subventral ridges lying anterior to tooth apex. Buccal wall mostly 1.6–2.0 µm thick. Distance between tooth apex and opposite wall of buccal cavity 10–11 µm. Pharynx 444–506 µm long, heavily muscular and practically cylindrical. Pharyngeal musculature surrounding the posterior 24–28% of buccal cavity. Nerve ring situated at anterior third of neck length. Cardia simple. Rectum nearly as long as anal body diameter.

Female

Genital system amphidelphic, each gonad as long as 4.0–8.8 body diameters or occupying 12–26% of body length. Vulva transverse with small sclerotized lips. Ovaries reflexed, well developed but rarely reaching the uterus–oviduct junction. Uterine eggs one to four at a time, 66–86 by 48–58 µm. Distance between posterior end of pharynx and vulva 1.1–1.3 times as long as pharynx. Vulva–anus distance equal to 2.4–3.0 tail lengths. Tail long and slender, 220–280 µm long, occupying 10–13% of entire length of body, first conical then tapering gradually to become almost cylindrical, ventrally curved on its tip; 8–10 µm wide at posterior third. Caudal spinneret terminal, subterminal papillae very small.

Male

Males are much less frequent than females: it is good when one male can be found among a hundred females. The general morphology is similar to that of the female but the tail is relatively and absolutely shorter. Genital system diorchic, testes opposite, outstretched. Spicula very long and slender, 102 µm in length and about 4 µm in width, twice as long as anal body diameter. Lateral guiding pieces slen- der. Gubernaculum thin, 22 µm long. Precloacal supplements 15 + 5 (15 normal and five reduced), regularly spaced. Tail 166 µm long, 9.2% of entire length of body; ventro-medial or ventro-lateral caudal papillae small, six pairs.

Remarks

Mononchus truncatus was described by Bastian (1865) from an aquatic habitat near Falmouth, England. Clark (1960) gave a redescription of this species on the basis of specimens collected at the type locality, and designated a female as neotype. Baqri and Jairajpuri (1972) when giving a comprehensive description of M. aquaticus Coetzee, 1968 , a related species of M. truncatus , compared the former with the topotypes of Clark, and gave some morphometric data of the latter species. Finally, Coomans and Khan (1981) published a fine and exact drawing of the anterior end (buccal region) of Clark’s neotype.

According to the above publications, the type / neotype specimens of M. truncatus are characterized by the following main morphometric structures (see also Table 1). Females: L = 1.6–2.1 mm; a = 26–40; b = 3.4–4.3; c = 6.4–8.6; c’ = 6–8; V = 48–55%; labial width 27–28 µm; length of buccal capsule 43–50 µm; position of dorsal tooth apex at 23–28%; buccal length 1.7 times the lip region width; tail 230–283 µm long .

These morphometric data characterize this species well. Hence, the “real” Mononchus truncatus is a medium-sized representative of the genus with an average body length of 1.86 mm, possessing a comparatively narrow labial region, large buccal cavity, relative posterior position of the dorsal tooth apex, and an elongated tail. To make this characterization more unique, some further morphological features should be added (see the above description).

The specimens studied here are from various places of the littoral zone of Lake Balaton, Hungary. They were collected in the summer months of the years 1992–1994 by the present author. On Table 1 the measurements of these specimens are compared with those of the type or neotype specimens of Mononchus truncatus . It can be seen that the populations from the Balaton region well correspond to the criteria of the “real” M. truncatus .

Other publications also contain adequate descriptions of this species. Andrássy (1985; as M. bellus ): L = 1.54–1.79; labial width 24–26 µm; buccal capsule 40–47 µm; tooth apex 30–33%; c’ = 6.0–8.2.

Mononchus species L (mm) a b c c’ V Lip r. width Buccal Tooth (µm) length apex (µm) (%)

Tail length Supple- (µm) ments

Spicula (µm)

agilis ♀ 2.9–3.1 17–19 3.4–3.7 9.8–11.6 3.2–3.9 51–55 45–49 81–84 12–14 Gagarin and Mat., 2004 ♂ 2.8–3.2 18–25 3.6–3.8 12.0–15.1 2.0–2.7

268–294 30–31 186–192

altiplanicus 2.6–2.8 38–42 3.7–3.8 7.4–8.6 7.7–8.7 53–56 31–33 57–61 28– 30 sp. nov. –

angarensis 5.1–5.6 37–43 4.6–5.3 16–19 2.5 48–58 70 (?) 81–86 15–25 Gagarin, 1984 4.6–4.8 29–45 3.5–4.0 17–24

aquaticus 1.2–1.7 20–37 4.2–5.0 8–12 5–6 46–59 18–24 26–32 20–25 Coetzee, 1968 1.5–1.7 26–32 4.3–4.9 11–26

clarki 1.8 25 3.5 33 2.0 59–60 28 42 26 Altherr, 1972 –

himalayensis 1.6–1.9 33–38 3.6–3.7 5.4–6.5 8.8–10.4 48–54 23–26 40–47 25–31 Rawat and Ahmad, 2000 –

italicus 1.06 28 3.7 14.9 2.4 54 22 33 30 Andrássy, 1959 –

laminatus 1.5–1.9 21–32 4.2–4.7 9.7–12.0 3.6–4.9 50–55 23–25 29–31 19–23 Zullini et al., 2002 –

loofi 1.1–1.3 26–30 5.0–5.6 9.4–10.9 3.9–4.8 50–53 16–18 21–23 28–33 Winiszewska, 1998 –

maduei 3.5–4.8 24–29 4.0–5.0 18–23 2.0 55–62 26–30 47–55 12–14 Schneider, 1925 3.4–4.3 28–34 4.2–5.6 26–39

medius 1.4–1.8 32–38 3.7–4.4 6.6–8.1 7.7–8.5 50–52 20–21 35–37 31–34 313–368

288–324

120–200

54

255–305

71

155–184

112–134

–

37–39

10–13

–

–

–

–

– –

300–330

38–46

–

–

–

–

–

170–210(12-) 22–27 120 205–225 – –

sp. nov. –

mulveyi 2.8–3.4 35–44 2.8–3.3 16–20 2.5–2.8 50–60 33–36 54–58 17–20 170–200 22–26 + 6 110–130 Andrássy, 1985 2.7–3.0 30–33 3.1–3.3 20–23

niddensis 2.6–3.5 32–43 3.8–4.2 12–15 5–6 51–56 28–32 46–60 12–16 200–250 26–33 134–140 Skwarra, 1921 2.5–3.5 30–38 3.3–3.7 12–17

nudus 1.6–2.1 22–35 3.9–4.6 9–12 2.8–4.1 49–57 22 26–44 22–24 176 – – Gagarin, 1991 –

oblongus 1.6–1.9 25–29 3.5–3.7 6.0–7.1 7.5–9.0 52–54 22–23 48–51 21–23 264–276 – –

sp. nov. –

pulcher 1.7–2.1 35–39 4.4–4.8 8.7–9.7 6–7 49–52 23–25 32–38 20–22 190–220 Andrássy, 1993 –

sandur 1.5–1.8 27–38 3.6–4.8 4.5–7.6 7.2–10.8 47–56 18–24 28–35 23–35 224–306 Eisendle, 2008 1.2–1.7 29–35 3.7–4.0 7.9–11.4 3.8–5.1

sinensis 1.3–1.8 19–38 4.0–4.6 7.2–8.7 4.0–6.7 47–50 20–22 32–34 25 170–205 Soni et al., 1983 –

superbus 5.0–6.4 44–50 3.8–4.5 13.0–13.2 5–6 51–53 52–56 72–80 23–24 370–420 Mulvey, 1978 4.5–6.0 39–46 4.0–4.6 19.5–24.0

syrmatus 1.6–1.7 32–35 3.5–3.9 4.2–5.0 13–15 47–50 25–27 38–42 29–32 344–390 Andrássy, 2008 –

tajmiris 3.2–4.4 17–18 3.2–3.5 13–20 1.9–2.5 55–60 40–44 105–123 16–27 253 Gagarin, 1991 3.4–4.2 18–21 3.4–3.9 16–20

truncatus 1.5–2.1 26–40 3.4–4.2 5.8–8.4 6–8 48–55 24–28 40–50 25–32 200–280 Bastian, 1865 1.7–2.0 32–45 3.9–4.1 9–10

tunbridgensis 0.9–1.4 20–35 4.2–5.3 9–11 4.0–5.8 51–55 14–16 18–20 10–12 100–150 Bastian, 1865 1.2–1.3 34 4.6–4.9 13

–

16–18

–

36–40

–

41–47

15–22

16–17

–

57–68

–

160–190

–

90–110

85–110

55–60

Chaves (1990; as M. bellus ): L = 1.9–2.2 mm; labial width 26–28 µm; buccal capsule 44–49 µm; tooth apex 26–32%; c’ = 5.3–7.3.

Jiménez-Guirado and Peña-Santiago (1991): L = 1.52–2.17; labial width 25–30 µm; buccal capsule 37–49 µm; tooth apex 23–29%; c’ = 5.8–8.8.

De Bruin and Heyns (1992): L = 1.66–2.15 mm; labial width 23–28 µm; buccal capsule 42–49 µm; tooth apex 21–29%; c’ = 6.6–9.5.

Eyualem and Coomans (1997): L = 1.46–1.49 mm; labial width 23–25 µm; buccal capsule 39–41 µm; c’ = 6.0–7.2.

According to the rich literary data on “ Mononchus truncatus ”, this species appears to have a worldwide distribution. Whether, however, all these data actually refer to M. truncatus or to one or other related species, cannot be resolved.

Key to Mononchus species

1. Large species, 2.6–6.4 mm .............................................. 2

Smaller species, 0.9–2.1 mm ............................................. 9

2. Tail very short, about two anal body diameters long...................... 3

Tail longer, (3–) 4–9 anal body diameters................................ 6

3. Posterior third of tail digitate, ventrally curved........... mulveyi Andrássy

Posterior third of tail not digitate, more or less straight................... 4

4. Buccal cavity 100–120 µm, nearly thrice as long as wide............................................................................. tajmiris Gagarin

Buccal cavity 50–90 µm long, about twice as long as wide................ 5

5. Buccal cavity 80–90 µm long; spicula 300 µm long...... angarensis Gagarin

Buccal cavity about 50 µm long; spicula 120 µm long.... maduei Schneider

6. Body 5.0– 6.4 mm long................................... superbus Mulvey

Body 2.6–3.5 mm long.................................................. 7

7. Buccal cavity 80–84 µm long; tail as long as 3–4 anal body diameters................................................. agilis Gagarin and Mataphonov

Buccal cavity 46–60 µm long; tail as long as 5–9 anal body diameters..... 8

8. Dorsal tooth apex at 12–16%; tail 5–6 times the anal body width long............................................................... niddensis Skwarra

Dorsal tooth apex at 28–30 %; tail 8–9 times the anal body width long............................................................. altiplanicus sp. nov.

9. Monodelphic species.................................... italicus Andrássy

Didelphic species...................................................... 10

10. Tail quite short, 1.5–2 anal body diameters, spinneret subdorsal........................................................................ clarki Altherr

Tail 3 anal body diameters or longer (c’ = up to 15), spinneret terminal............................................................................ 11

11. Buccal cavity small, 18–23 µm long.................................... 12

Buccal cavity larger, 26–50 µm long.................................... 13

12. Buccal cavity very narrow, nearly thrice as long as wide, dorsal tooth apex quite close to the beginning of buccal capsule......... tunbridgensis Bastian

Buccal cavity more spacious, twice as long as wide, dorsal tooth apex at onethird of buccal capsule............................. loofi Winiszewska

13. Tail 7–15 (mostly 9–14) times the anal body width long................. 14

Tail 3–8 (mostly 4–7) times the anal body width long.................... 16

14. Tail 340–390 µm, as long as 13–15 anal body diameters........................................................................... syrmatus Andrássy

Tail 220–300 µm, as long as 8–11 anal body diameters.................. 15

15. Buccal cavity 40–47 µm long; one prevulval papilla present.......................................................... himalayensis Rawat and Ahmad

Buccal cavity 28–35 µm long; prevulval papilla absent...... sandur Eisendle

16. Vulval lips not sclerotized......................... sinensis Soni and Nama

Vulval lips distinctly sclerotized........................................ 17

17. Dorsal tooth apex at about 30 %, transversal subventral ribs anterior to tooth apex.................................................................. 18

Dorsal tooth apex at 20–25%, transversal subventral ribs at level of or posterior to tooth apex................................................ 19

18. Lip region wider, 24–28 µm; cylindrical portion of tail 10–12 µm thick............................................................. truncatus Bastian

Lip region narrower, 20 µm; cylindrical portion of tail 5–7 µm thick................................................................... medius sp. nov.

19. Amphid aperture posterior to dorsal tooth...................................................................... laminatus Zullini, Loof and Bongers

Amphid aperture anterior to dorsal tooth.............................. 20

20. Tail 3–4 anal body widths long............................. nudus Gagarin

Tail 5–7 anal body widths long......................................... 21

21. Buccal cavity oblong, 47–50 µm long, longer than two labial diameters.............................................................. oblongus sp. nov.

Buccal cavity barrel-shaped, 26–38 µm long, conspicuously shorter than two labial diameters....................................................... 22

22. Body 1.7–2.1 mm long; buccal cavity 32–38 µm long, twice as long as wide........................................................... pulcher Andrássy

Body 1.2–1.7 mm long; buccal cavity 26–32 µm long, two and a half times as long as wide........................................... aquaticus Coetzee

Figures

Figure 8. Mononchus truncatus Bastian, 1865. (A) Anterior end; (B) vulval region; (C, D) female posterior end; (E) cloacal region of male. Scale bars 20 µm each.

Figure 9. Mononchus truncatus Bastian, 1865. (A–C) Anterior end; (D, E) vulval region with two and four eggs, respectively; (F–H) female posterior end; (I) male posterior end; (J) cloacal region of male.