Dichromadora media, Liang & Guo & Wang, 2024

Liang, Huixin, Guo, Wen & Wang, Chunming, 2024, Two new species of Hypodontolaiminae (Nematoda, Chromadorida, Chromadoridae) from the Yellow Sea with a phylogenetic analysis in the subfamily, ZooKeys 1190, pp. 281-302 : 281

Dichromadora media sp. nov.

Figs 1 , 2

Diagnosis.

Medium body size, cuticle with transverse rows of dots and a lateral differentiation of two longitudinal larger dots, four long cephalic setae, buccal cavity large with one large, hollow and straight dorsal tooth and two small ventrosublateral teeth, amphidial fovea transverse oval in male and slit-shaped in female, pharynx with single posterior bulb, spicules curved and distally bifurcated, gubernaculum jointed, four (1+3) papilliform precloacal supplements, tail conical elongated with short spinneret.

Material examined.

Four males and three females were measured and studied. Holotype: ♂ 1 on slide 22ZJT8-1-2; Paratypes: ♂ 2 on 22ZJT8-1-2, ♂ 3 on 22ZJT8-1-2, ♂ 4 on 22ZJT8-2-5, ♀ 1 on 22ZJT8-2-7, ♀ 2 on 22ZJT8-2-7, and ♀ 3 on 22ZJT8-2-6.

Type locality and habitat.

Rizhao coast, Shandong Province, China, 35°27′N, 119°35′E, 0-2 cm sediment depth, sandy sediment.

Measurements.

All measurement data are given in Table 3 .

Description.

Males. Body cylindrical and medium sized (881-925 μm in length). Cuticle with transverse rows of dots and a differentiation consisting of two longitudinal rows of distinct larger dots starting posterior the amphidial fovea and extending to the tail tip (2 μm in width). Transverse bars connecting the two larger dots beginning from the middle of the pharynx to the middle of tail. Somatic setae present sparsely along the lateral differentiation in two longitudinal rows, short in the head and tail (9 μm in length), long in the middle of the body (12 μm in length). Inner and outer labial sensilla papilliform. Four cephalic sensilla setiform at the level of amphidial fovea (1.20-1.36 head diameter in length). Head blunt. Amphidial fovea oval (4 µm in width and 3 µm in length), small (26.7%-28.6% corresponding body diameter) and situated 0.47-0.57 head diameter from the anterior end. Buccal cavity cuticularized with a large, hollow and straight dorsal tooth and two small ventrosublateral teeth. Cheilostoma short with longitudinal cuticularized ribs. Pharynx cylindrical, anterior region surrounding buccal cavity slightly swollen, posterior region swollen into an elongated single bulb with plasmatic interruptions resembling a double bulb (18.8-20.0% of pharynx length). Nerve ring slightly posterior to middle pharynx region (53.6-60.9% of pharynx length). Renette cell of secretory-excretory system situated posterior to pharynx bulb, excretory pore located at anterior buccal cavity (6-8 μm from anterior end). Cardia not observed.

The reproductive system monorchid, with extended testis located to the right of intestine. Spicules equal and slightly curved, 23-25 μm (1.0-1.1 cloacal body diameter) along arc, proximal end slightly widened and distal end bifurcated. Gubernaculum jointed without apophysis. Four (1 + 3) precloacal supplements papilliform, anterior three supplements closely distanced and posteriormost supplement distant from the three anterior ones, distance between the supplements 9-12 μm, 8-9 μm, 16-19 μm, respectively, and posteriormost supplement 7-8 μm from cloaca. Tail elongated conical, gradually tapering, 4.5-5.0 cloacal body diameters. Spinneret very short, 1-2 μm in length.

Females. Similar to males in most characteristics. Amphidial fovea slit-like (50.0% corresponding body diameter). Cephalic setae short (10-11 μm in length). Reproductive system didelphic, with opposed and reflexed ovaries. Anterior ovary to right of intestine and posterior ovary to left of intestine. Eggs oval shaped, 8-10 × 10-11 μm. Vulva at the middle of the total body. Vagina short.

Etymology.

Species epithet media refers to the medium body size.

Remarks.

Dichromadora media sp. nov. differs from all other species of the genus Dichromadora by the amphidial fovea shape and jointed gubernaculum and it is similar to D. dissipata , D. quadripapillata , and D. sinica in body length and precloacal supplements number. However, it differs from D. dissipata in cephalic setae length (10-19 μm vs 9-9.5 μm), spicules length (23-25 μm vs 39 μm), gubernaculum shape (double-jointed without apophysis vs not jointed with dorsal apophysis) and precloacal supplements (1+3 vs 5); differs from D. quadripapillata in cephalic setae length (10-19 μm vs 4-5 μm), spicules shape (slightly curved and distally bifurcated vs curved with pointed distal end) and precloacal supplements shape (papilliform vs cup-shaped); differs from D. sinica in cuticle differentiation (lateral differentiation with transverse bars vs lateral differentiation without transverse bars), pharynx bulb shape (single bulb with plastic interruptions vs double bulb), spicules shape (slightly curved and distally bifurcated vs distal end with a hook), gubernaculum shape (jointed vs not jointed), and precloacal supplements arrangement (1+3 vs 3+1).

Dichromadora media sp. nov. shows a close relationship with D. sinica in the phylogenetic trees (Figs 5 , 6 ) based on rDNA sequences and it differs by 2% (39 in 1656 bp, including two gaps) in SSU and 5% (38 in 770 bp, including four gaps) in LSU D2-D3 fragment, but they can be morphologically differentiated based on pharynx bulb shape, spicule shape, gubernaculum shape and precloacal supplements.

Figures

Figure 1. Dichromadora media sp. nov. A lateral view of male anterior region showing cuticle and amphidial fovea (holotype) B lateral view of male buccal cavity (holotype); C lateral view of male anterior region showing pharyngeal region (holotype) D lateral view of female anterior region showing buccal cavity, amphidial fovea and pharyngeal region (22 ZJT 8 - 2 - 7) E lateral view of female whole body (22 ZJT 8 - 2 - 7) F lateral view of male posterior body, showing precloacal supplements and tail (holotype); G lateral view of spicules and gubernaculum (22 ZJT 8 - 2 - 5) H lateral view of female posterior body showing tail (22 ZJT 8 - 2 - 7). Scale bars: 20 µm (A-D, F, H); 50 µm (E).

Figure 2. Dichromadora media sp. nov. A lateral view of male anterior region showing tooth (arrow) (holotype) B lateral view of male anterior region showing cuticle, amphidial fovea (arrow) (holotype) C lateral view of male anterior region showing pharyngeal region (holotype) D lateral view of male posterior body, showing spicules (holotype) E lateral view of male posterior body, showing gubernaculum (22 ZJT 8 - 1 - 2) F lateral view of male posterior body, showing precloacal supplements (arrows) (holotype) G lateral view of female anterior region showing amphidial fovea (arrow) (22 ZJT 8 - 1 - 2) H lateral view of distal end of spicules (22 ZJT 8 - 2 - 5). Scale bars: 20 µm.

Figure 5. Bayesian inference tree of the subfamily Hypodontolaiminae inferred from Small Subunit (SSU) sequences under the general time-reversible (GTR) + gamma distribution (G) + proportion of invariable sites (I) model. Posterior probability (left) and bootstrap values (right) are given on corresponding clades. The sequences obtained in this study are shown in bold. The scales indicate substitutions per site.

Figure 6. Bayesian inference tree of the subfamily Hypodontolaiminae inferred from the D 2 - D 3 fragment of Large Subunit (LSU) sequences under the general time-reversible (GTR) + gamma distribution (G) model. Posterior probability (left) and bootstrap values (right) are given on corresponding clades. The sequences obtained in this study are shown in bold. The scales indicate substitutions per site.