Aphelenchoides spicomucronatus Truskova, 1973

Girgan, Chantelle, Swart, Antoinette, Marais, Mariette & Fourie, Hendrika, 2018, Aphelenchoides spp. (Nematoda: Aphelenchida) and Panagrolaimus leperisini (Nematoda: Rhabditida) found associated with grass seeds in the Telperion Nature Reserve, South Africa, Zootaxa 4370 (2), pp. 137-155 : 146-149

Aphelenchoides spicomucronatus Truskova, 1973

( Fig. 5 & 6 )

Aphelenchoides spicomucronatus was first described from the roots of Glycine hispida (Moench) Maxim. ( Truskova, 1973) . However, only three females were examined in describing the species. It was reported for the second time by Rashid et al. (1986) from soil samples collected in Brazil. To date these are the only reports of this species.

Measurements. See table 4.

Description. Female (n = 1): Body slender, habitus slightly curved ventrally. Cuticle finely annulated, annule width approximately 1 µm at mid-body. Lateral field marked with four incisures ( Fig. 5B ). Head slightly offset. Lip region flattened anteriorly ( Fig. 5A ) 3 µm high and 6 µm broad. Stylet 11 µm long with distinct basal swellings. Median bulb spherical in shape with prominent centrally located valves ( Fig. 5A ). Nerve ring situated 74 µm from anterior end, less than one corresponding body width from base of median bulb. Excretory pore 85 µm from anterior end, opposite posterior end of nerve ring ( Fig. 5A ). Ovary outstretched with oocytes arranged in a single row ( Fig. 5D & 6A ). Spermatheca containing spherical sperm cells ( Fig. 6B ). Sperm cells also observed in uterus ( Fig. 6B ). Vulval lips slightly protruding with the vagina occupying less than half the corresponding body width, curving anteriorly. Post-vulval uterine sac 57 µm in length, about three times vulval body width and shorter than half vulva-anus distance ( Fig. 5E & 6D ). Tail conical, 40 µm long with a centrally located mucro ( Fig. 5C & 6C ). Anus distinct, with the anterior lip protruding slightly.

Male: Not found.

Discussion. The female Aphelenchoides specimen recovered from Eragrostis gummiflua samples was identified as A. spicomucronatus based on the characteristic tail mucro shape and presence of four lateral field incisures. Measurements and morphological details match those of Truskova (1973) and Rashid et al. (1986). This specimen differs only in having the excretory pore situated opposite the posterior end of the nerve ring. In both published accounts of A. spicomucronatus , the excretory pore is situated between the median bulb and the nerve ring. However, Rashid et al. (1986) did state that the excretory pore position varied from opposite the median bulb to one median bulb length posterior to it.

Other discrepancies were noted in the above-mentioned descriptions. In Rashid et al. (1986) the spermathecae of 19 females were reported to be empty. However, the original description by Truskova (1973) indicated that sperm cells were observed in the spermatheca and PUS, in all three specimens studied. Sperm cells were seen in the spermatheca of our Telperion specimen. In the original description, the lateral field was described as not visible, but Rashid et al. (1986) observed four incisures in the lateral field in cross sections. Our South African specimen has a lateral field with four incisures. This species is reported for the first time from South Africa. The specimen (accession number 50544) was deposited in the NCN.

Relationships. The Aphelenchoides specimen from Telperion was compared to those species with a tail with one (or sometimes two) terminal mucronate structures and four incisures in the lateral field ( Shahina 1996). Aphelenchoides haguei Maslen, 1979 and A. tuzeti B’Chir, 1979 both have longer stylets - 13 µm and 14 µm, respectively - compared to 11 µm in A. spicomucronatus . The following species have a slightly more posterior vulva position (vs. 69% in the South African species): A. absari Husain & Khan, 1967 (69–77%), A. brassicae Edward & Misra, 1969 (68–74%), A. cyrtus Paesler, 1959 (70–73%), and A. echinocaudatus Haque, 1968 (72%). A. parasaprophilus Sanwal, 1965 (680–750 µm), and A. subtenius ( Cobb, 1926) Steiner & Buhrer, 1932 (870–1150 µm) are larger (L = 669 µm for A. spicomucronatus ) and can also be differentiated by tail shape. A. eradicitus Eroshenko, 1968 (300–310 µm), A. parabicaudatus Shavrov, 1967 (310-350 µm), and A. platycephalus Eroshenko, 1968 (240-270 µm) are much smaller species. A. eradicitus also has a shorter stylet (10 µm compared to 11 µm in A. spicomucronatus ) and more anterior vulva (V = 64% vs. 69%). A. parabicaudatus can be differentiated by its shorter stylet (8 µm vs. 11 µm) and bifurcate tail tip. Aphelenchoides platycephalus has a more anterior nerve ring and a longer mucro.

Aphelenchoides richardsoni Grewal, Siddiqi & Atkey, 1992 is the most morphologically similar species in having more developed stylet knobs than the South African specimens. Other closely related species based on morphology are A. daubichaensis Eroshenko, 1968 , and A. tsalolikhini Ryss, 1993 . A. daubichaensis differs in tail shape, with a more centrally located terminal mucro and a shorter tail length (29–31 µm compared to 40 µm in A. spicomucronatus ). Aphelenchoides tsalolikhini also has a longer tail (c’ = 4.6–6.2 compared to 3.3 in A. spicomucronatus ), and different tail shape (long, thorn-like, ventrally situated mucro).

Figures

FIGURE 5. Aphelenchoides spicomucronatus female. A: Anterior region; B: Lateral field at mid-body; C: Tail region; D: Anterior end of reproductive system showing arrangement of oocytes; E: Vulval region showing post-vulval uterine sac.

FIGURE 6. Aphelenchoides spicomucronatus female. A: Anterior end of reproductive system showing arrangement of oocytes; B: Genital tract with arrow indicating spermatheca with sperm cells; C: Tail region; D: Vulval region showing postvulval uterine sac.