Axonolaimus dimorphous, Liang & Guo & Wang, 2024

Liang, Huixin, Guo, Wen & Wang, Chunming, 2024, Two new species of Nematoda: Gairleanema pulchra sp. nov. (Tripyloididae) and Axonolaimus dimorphous sp. nov. (Axonolaimidae) from the Yellow Sea, China, Zootaxa 5447 (4), pp. 547-561 : 554-557

Axonolaimus dimorphous sp. nov.

( Figures 3–4 , Table 3 )

Type material. Four males and three females were measured and studied. Holotype: ♂ 1 on 22LJW3–2–4; paratypes: ♂ 2 on 22LJW3–1–11, ♂ 3 on 22LJW3–4–2, ♂ 4 on 22LJW3–4–2, ♀ 1 on 22LJW3–1–12, ♀ 2 on 22LJW3–4–4 and ♀ 3 on 22LJW3–3–16.

Type locality and habitat. Specimens were collected from intertidal muddy sediment at Rizhao coast, Shandong Province, China, 35°18′N, 119°31′E; 0–2 cm sediment depth .

Etymology. Species epithet dimorphous refers to amphidial fovea different in male and female.

Descriptions

Males. Body cylindrical, tapering slightly towards both extremities. Cuticle finely striated. Two lateral dorsal and two latero-ventral rows of somatic setae present along entire body, 5–7 µm in length.Anterior body end blunt and slightly rounded, lips short. Inner and outer labial sensilla papilliform, four cephalic setae, 1.2–1.4 c.b.d. (corresponding body diameter) in length. Four cervical setae, 7–8 µm in length, situated slightly posterior to amphids. Amphidial fovea elongated loop-shaped, situated slightly posterior to cephalic setae and slightly longer than buccal cavity. Buccal cavity funnel-shaped, with cuticularized walls, 16–18 µm in depth, 6 µm in width, without odontia. Pharynx cylindrical with posterior portion slightly widened. Nerve ring located at about two-thirds of pharynx length from anterior end. Secretory-excretory gland situated 40 µm posterior to pharynx end, secretory-excretory pore 34 µm from anterior end. Cardia short, triangular shaped.

Reproductive system didelphic, with two opposed outstretched testes. Anterior testis to the left of intestine, posterior testis to the right of intestine. Spicules strongly cuticularized and arcuated, 1.2 cloacal body diameters along arc. Gubernaculum parallel to the distal end of spicules, with dorsal apophysis slightly directed to caudal position. Precloacal supplements absent. Tail conico-cylindrical with two rows of subventral setae and sparse subdorsal setae. Three caudal glands present.

Females. Similar to males in most characteristics. Amphidial fovea loop-shaped. Reproductive system with two opposed outstretched ovaries, anterior ovary to the left of intestine and posterior ovary to the right of intestine. Spermatheca not observed. Vulva located slightly posterior to mid-body.

Differential diagnosis and discussion

Axonolaimus dimorphous sp. nov. is characterized by four long cephalic setae, amphidial fovea elongated loop-shaped in males and loop-shaped in females, amphidial fovea at level of subcephalic setae, spicules arcuated, gubernaculum with dorsal apophysis slightly directed to caudal position and tail conico-cylindrical with caudal setae.

Axonolaimus dimorphous sp. nov. differs from the other species in presenting amphidial fovea elongated loop-shaped in males and loop-shaped in females. It is similar to A. demani , A. filipjevi , A. helgolandicus , A. hexapilus , A. orcombensis , A. tenuis and A. typicus in the amphidial fovea shape in females, but it differs from A. demani in the body length (1452–1751 μm vs. 800–1187 μm), cephalic setae length (14–16 μm vs. 3–5 μm), spicules length (27–29 μm vs. 18 μm), gubernaculum apophysis length (8–9 μm vs. 13 μm), and tail length (7.3–8.3 anal body diameter vs. 5–6.5 anal body diameter) ( Gerlach 1957); differs from A. filipjevi in the cephalic setae length (1.2–1.5 head diameter vs. 0.9 head diameter), presence of cervical setae (absent in A. filipjevi ), spicules length (1.2 anal body diameter vs. 1 anal body diameter), gubernaculum apophysis shape (dorsal, slightly directed to caudal position vs. dorsal-caudal directed) (calculated based on Timm 1954); differs from A. helgolandicus in spicules length (27–29 μm vs. 42 μm), gubernaculum apophysis shape and length (dorsal slightly directed to caudal position, 8–9 μm vs. dorsal-caudal directed, 24 μm in length), precloacal supplements absent (16 tiny preanal papillae in A. helgolandicus ) (calculated based on Lorenzen 1971); differs from A. hexapilus in the cephalic setae length (14–16 μm vs. 21–24 μm), spicules length (27–29 μm vs. 39 μm), precloacal supplements absent (present in A. hexapilus ), and tail shape (conico-cylindrical vs. obtuse conoid); differs from A. orcombensis in the body length (1452–1752 μm vs. 2980–3620 μm), cephalic setae length (14–16 μm vs. 23–27 μm), cervical setae (four cervical setae vs. eight long cervical setae), spicules length (27–29 μm vs. 43–48 μm), precloacal supplements absent (20–30 precloacal supplements in A. orcombensis ); differs from A. tenuis in the body length (1452–1752 μm vs. 3400–3800 μm), cephalic setae length (1.2–1.5 head diameter vs. 3 head diameter), spicules shape (arcuated vs. distal end with a hook), tail shape (tail conico-cylindrical vs. tail blunt); differs from A. typicus in the cephalic setae length (1.2–1.5 head diameter vs. 0.3 head diameter), presence of cervical setae (absent in A. typicus ), gubernaculum apophysis shape (dorsal slightly directed to caudal position vs. caudal directed).

Thus, 34 species should be considered valid and an identification key to valid species of the genus Axonolaimus is provided below.

Figures

FIGURE 3. Axonolaimus dimorphous sp. nov. A. Lateral view of male anterior end, showing amphidial fovea and cephalic setae; B. Lateral view of female anterior portion, showing amphidial fovea; C. Lateral view of male anterior portion, showing buccal cavity and pharynx region; D. Lateral view of female anterior portion, showing buccal cavity and pharynx region; E. Lateral view of male posterior portion; showing spicules and gubernaculum; F. Lateral view of female posterior portion. G. Lateral view of female entire body. Scales: A, B = 20 μm; C, D, E, F = 30 μm; G = 50 μm.

FIGURE 4. Axonolaimus dimorphous sp. nov. A. Lateral view of male anterior end, showing amphidial fovea and cephalic setae; B. Lateral view of female anterior portion, showing amphidial fovea; C. Lateral view of male posterior portion; showing spicules; D. Lateral view of male posterior portion; showing gubernaculum. Scales: A, B, C, D = 20 μm.