Metadasynemoides Haspeslagh, 1973

Leduc, Daniel, 2024, Four new free-living marine nematode species (Plectida: Ceramonematidae) and two new species records (Desmodorida: Desmodorinae) from Rangitāhua / Kermadec Islands, Aotearoa / New Zealand, European Journal of Taxonomy 970, pp. 138-174 : 155-156

Metadasynemoides Haspeslagh, 1973

Type species

Metadasynemoides longicollis (Gerlach, 1952) Haspeslagh, 1973 .

Diagnosis (modified from Tchesunov & Mijutina 2002 and Holovachov 2014)

Body cuticle consists of 400–1000 equally narrow annules. Zygapophyses indistinct under light microscopy. Cuticular crests extend from near anterior margin of cephalic capsule to terminal cone. Lateral lines (parallel grooves as seen using SEM) may be present on cuticle beginning from amphids and extending close to level of anus/cloaca. Labial region distinctly set off from cephalic capsule. Setose outer labial sensilla and setose cephalic sensilla subequal in length and arranged in two separate but close circles both inserted on labial region anterior to margin of cephalic capsule. Amphid spirally coiled in 1–2 turns, loop-shaped, rounded or of other shape, often differing in shape between males and females.

Remarks

A key to all five valid species described prior to the present study is provided by Tchesunov & Miljutina (2002). Cuticular structures of Metadasynemoides cristatus (Gerlach, 1957) Haspeslagh, 1973 such as lateral lines were described in detail by Nicholas & Stewart (1990) based on light and electron microscopy.

List of valid species of Metadasynemoides Haspeslagh, 1973

M. cristatus (Gerlach, 1957) Haspeslagh, 1973

M. labiatus Tchesunov & Miljutina, 2022

M. latus (Gerlach, 1957) Haspeslagh, 1973

M. longicollis (Gerlach, 1952) Haspeslagh, 1973

M. spinosus (Gerlach, 1963) Tchesunov & Miljutina, 2002

M. taihua sp. nov.

Key to species of Metadasynemoides Haspeslagh, 1973 (modified from Tchesunov & Miljutina 2002)

1. Body length about 1500 µm or less .................................................................................................. 2

– Body length 2000–3000 µm. Cephalic setae 17 µm long; circles of outer labial and cephalic setae close to each other. Cephalic capsule stout and anteriorly truncated .................................................. ............................................................................... M. longicollis (Gerlach, 1952) Haspeslagh, 1973

2. Cephalic setae 5–12 µm long (up to 70% cbd) ................................................................................. 3

– Cephalic setae 24 µm long (> 100% cbd). Cephalic capsule elongate, tapered anteriorly. Amphid loop-shaped, with longer ventral branch ............................................................................................ ............................................................... M. spinosus (Gerlach, 1963) Tchesunov & Miljutina, 2002

3. Tail about 4.5–5.0 anal /cloacal body diameters long; ratio of c> 11. Amphid rounded, at least in females .............................................................................................................................................. 4

– Tail about 8–11 anal/ cloacal body diameters long; ratio of c <11. Cephalic capsule elongate, tapered anteriorly. Amphid of female loop-shaped, with longer ventral branch extending to the second postcephalic annule .......................................................... M. labiatus Tchesunov & Miljutina, 2022

4. Cephalic capsule stout and truncated anteriorly, cephalic ratio near 1 ............................................. 5

– Cephalic capsule elongate and tapered anteriorly. Cephalic ratio> 1. In male, amphid loop-shaped, with longer ventral branch extending to postcephalic annules. Outer labial setae longer than cephalic setae ......................................................................... M. cristatus (Gerlach, 1957) Haspeslagh, 1973

5. Body length about 1000–1200 µm, ratio of b = 4, ratio of c = 13–14. Male with spiral amphid with two turns ........................................................................ M. latus (Gerlach, 1957) Haspeslagh, 1973

– Body length about 1400–1500 µm, ratio of b = 6, ratio of c = 9–11. Male with loop-shaped amphid ................................................................................................................................ M. taihua sp. nov.