Cactodera chenopodiae Feng & Wang & Xiao & Pereira & Xuan & Wang & Liu & Chen & Duan & Zhu 2018, n. sp.

Cactodera chenopodiae * n. sp.

(Figs. 1–5, Tables 1)

*specific epithet after the host, Chenopodium album L.,

Measurements. See Table 1.

Description. Females. Body ovate to rounded or subspherical in shape with small vulval cone (Fig. 1C, 1D), female body pearly-white (Fig. 1G, 1H). Females with small vulval cones having slightly protruding lips (Fig. 1C, 1D). Female full of eggs and gelatinous egg sac not observed (Fig. 1I). Outer cuticular layer marked by a rugose pattern. Head slightly set off from the elongate and protruding neck, stylet and stylet knobs well developed (Fig. 1A). Excretory pore located at same level as end of isthmus (Fig. 1B). Anus distinct (Fig.1E, 1F).

Cysts. Rounded to lemon-shaped, from light to dark brown with small vulval cone (Figs. 1K, 1L, 4A, 5F). Cyst surface with zigzag pattern at mid-body and not prominent on surface of the vulval cone (Fig. 4C, 4D). Cone is circumfenestrate and lacks an underbridge, bullae and vulval denticles (Fig. 1C, 1D, 4D). Anus distinct and encircled within a disc-like cuticular region (Fig. 4B).

Males. Not found.

J2s. Vermiform, tapering anteriorly and posteriorly (Fig. 2A). Stylet knobs rounded to slightly projecting anteriorly (Fig. 2B). Lip region slightly set off with four annuli. In en face view, an elongated labial disc surrounded by four submedial and two lateral lips (Fig. 4E, 5G). Excretory pore near level of gland lobe, hemizonid was one and a half annulus above excretory pore (Fig. 2B, 2E, 2F 5B). Lateral field with four lines with outer two ridges partially areolated along the body. (Figs. 2G, 4F, 5C). Tail tapering, with hyaline region; the hyaline region is often shorter than the stylet. Transition to hyaline region usually clearly demarcated by an outline that is V-shaped, U-shaped, or rarely sloping ventrally (Fig. 2C, 2D, 5D).

Eggs. Surface with heavy punctations visible both under LM and SEM (Figs. 1J, 4G–I). Only found inside cysts.

Type host and locality. Common lambsquarter, C. album in the Beiling Park, Shenyang, Liaoning province, China. Coordinates: 41°50’38” N, 123°25’44” E, 51 m a.s.l.

Type material. Holotype female, seven paratype females, twenty paratype cysts and twenty paratype J2s were deposited for curation in the collection of the Nematology Institute of Northern China (NINC), Shenyang Agricultural University, Shenyang, China.

Biology. Cactodera chenopodiae n. sp. was found on roots of C. album among other native vegetation of China. On the type host, the cyst nematode ranges from endoparasitic to semi-endoparasitic. Juveniles were detected on the roots of the host plant by acid fuchsin staining(Fig.3A). Moreover, some maturing juveniles (presumed to be sedentary J2s, J3s and J4s) were found with the anterior portion of their body penetrating into the roots (Fig. 3B–C).

Diagnosis and relationships. Cactodera chenopodiae n. sp. belongs to the genus Cactodera which includes species characterized by a small vulval cone and a circumfenestrate terminal pattern. The new species can be differentiated from the fourteen other Cactodera species by a combination of morphological and molecular characters.

The ranges of many morphological characters of C. chenopodiae overlap with those of other Cactodera species and isolates, including with certain C. cacti isolates from different regions of the US [e.g., Michigan, Graney & Bird (1990)]; yet, morphometric analyses of C. chenopodiae n. sp. demonstrate that the means for these morphological features are distinctive relative to C. cacti. For example, females of C. chenopodiae n. sp. have a larger L/W ratio [1.6 (1.4–1.7) vs. 1.2 (1.0–1.4)], and J2s have a smaller b ratio [3.8 (3.6–4.1) vs. 6 (5.6–6.8)] as well as a longer hyaline region [22.7 µm (17.5–28.4) vs. 17.6 µm (13.7–20.5)]. Cactodera chenopodiae n. sp. is also distinguished from C. milleri, known to parasitize common lambsquarter in Michigan, US (Graney & Bird, 1990), by the cyst having an anus set off within a distinctive disc-shaped cuticular pattern (Fig. 1E–F, 4B) and by having a greater fenestral diameter [23.5 µm (19.9–26.3) vs. 18.7 µm (14.3–22.0)]. Moreover, J2s stages have a larger b ratio [3.8 (3.6–4.1) vs. 2.9 (2.6–3.1)] and a longer hyaline region [22.7 µm (17.5–28.4) vs. 18.2 µm (14.6– 21.2)] when compared to C. milleri.

All measurements are in µm. a CV: coefficient of variation.

As for closely related species (i.e. based on molecular data), C. chenopodiae n. sp. is distinguished from C. estonica (Kirjanova & Krall, 1963) Krall & Krall, 1978, by the eggshell pattern (i.e., punctate in C. chenopodiae vs. smooth in C. estonica) and larger b ratio in J2s [3.8 (3.6–4.1) vs. 2.8 (2.7–2.9)]. In addition, C. chenopodiae n. sp. differs from C. rosae Cid del Prado & Miranda, 2008 by a longer hyaline region [22.7 µm (17.5–28.4) vs. 6.3 µm (4.0–6.8)]