Nannolaimoides brevicaudatus, Chu, Hao & Huang, 2023

Chu, Mengdi, Hao, Yingdong & Huang, Mian, 2023, Two new species of Chromadorida (Nematoda) from the intertidal zone of the Yellow Sea, China, Journal of Natural History 57 (25 - 28), pp. 1364-1376 : 1370-1375

Nannolaimoides brevicaudatus sp. n.

( Figures 3 , 4 and Table 2 )

Type material

Three males and two females were collected from the Lanshan beach of Rizhao coast along the Yellow Sea (35.083°N, 119.317°E). Holotype male on slide RZLS 13–23 , paratypes: males 2– 3 and females 1–2 on slides RZLS 13–34 , RZLS 12–3 , RZLS 11–5 and RZLS 11–2 , respectively.

Type locality and habitat

Holotype was found in the surface layer of muddy sediment at Lanshan beach of Rizhao.

Etymology

The specific name is derived from the Latin adjective brevis (short) and Latin adjective caudatus, referring to its relatively short tail within the genus.

Measurements

All measurement data are given in Table 2 .

Description

Male. Body long and slender. Cuticle characterised by transverse rows of punctations, with lateral differentiation consisting of irregular large dots formed from level of amphid to level of cloaca. On the tail, cuticular lateral differentiation consisting of two longitudinal rows of large dots. Cuticular pores present, sparsely distributed in cuticle. Somatic setae not observed. Head tapered or slightly rounded. Six inner labial sensilla setiform, 2 µm long; six outer labial sensilla setiform, 4–5 µm long, together with four 6–7 µm cephalic setae in one circle. Amphideal fovea multispiral, with five turns, 41–50% of corresponding body diameter in width, 6 µm from the head end. Buccal cavity cup-shaped, with a pointed dorsal tooth and two smaller subventral teeth. Pharynx cylindrical, slightly enlarged at base, not forming bulb. Cardia conical. Nerve ring surrounding the pharynx in the middle of its length. Excretory pore not observed. Tail conico-cylindrical, 4.3–4.9 times as long as body diameter at cloaca. Caudal seta absent. Caudal glands not observed.

Reproductive system diorchic, testes opposed, reflexed at ends. Spicules slightly S-shaped without central lamella, proximal end bent dorsally, distal end tapered, 1.3– 1.5 times as long as body diameter at cloaca. Gubernaculum paired, expanded distally and tapered proximally, without apophysis and distinct denticles. One precloacal papilla and 14 button-shaped precloacal supplements almost equally arranged with cuticle slight annulated between them. Posteriormost supplement 31–34 µm and anteriormost one 232–257 µm in front of cloaca.

Females. Similar to males in morphological features except tail slightly longer (139– 155 µm vs 117–128 µm). Reproductive system amphidelphic with two opposite and reflexed ovaries, anterior one to the right of the intestine, posterior one to the left. Vulva located at 56–59% body length from the anterior end. Spermatheca present.

Differential diagnosis and discussion

Nannolaimoides brevicaudatus sp. nov. is characterised by a slender body with irregular lateral differentiation, cephalic setae 6–7 µm long, multispiral amphideal fovea with five turns and close to head end, spicules slightly S-shaped, gubernaculum paired, expanded distally and pointed proximally without denticles, a precloacal papilla and 14 button-shaped precloacal supplements almost equally arranged, tail conico-cylindrical without caudal setae.

Genus Nannolaimoides Ott, 1972 belongs to the family Cyatholaimidae Filipjev, 1918 . It was previously classified in the subfamily Pomponematinae Gerlach and Riemann, 1973 ( Tchesunov 2014; Nemys eds 2022). However, according to Hodda̍s classification system ( Hodda 2022), Nannolaimoides was placed in the subfamily Cyatholaiminae (where the family Cyatholaimidae was divided into two subfamilies: Cyatholaiminae Filipjev, 1918 and Paracanthonchinae De-Coninck, 1965). Nannolaimus armatus Gerlach, 1964 has been designated as the type species for this genus, and accepted as Nannolaimoides armatus ( Gerlach, 1964) Ott, 1972 . Currently, three species have been documented worldwide within this genus, namely N. armatus ( Gerlach, 1964) Ott, 1972 , N. decoratus Ott, 1972 , and N. effilatus ( Boucher, 1976) Platt and Warwick 1988 .

The new species is similar to N. decoratus Ott, 1972 in tail length, but differs from the latter species in its slender body (a = 67.6–79.2 vs 32.0–41.8), precloacal supplements (a precloacal papilla and 14 button-shaped precloacal supplements vs a precloacal spine and 16–18 cup-shaped supplements) and tail with cuticular lateral differentiation of two longitudinal rows of large dots. The present species can be easily differentiated from the other two species, N. armatus and N. effilatus , by its relatively shorter conico-cylindrical tail. Both of the latter species have long filiform tails and different precloacal supplements. Nannolaimoides armatus has 17 cup-shaped precloacal supplements and N. effilatus has 10–14 papilliform precloacal supplements.

Key to identification of species of the genus Nannolaimoides including the new species, N. brevicaudatus

1. Tail long (c′> 9), filiform .................................................................................................................... 2

– Tail comparatively short (c′<6.5), conico-cylindrical ............................................................ 3

2. Males with 10–14 papilliform precloacal supplements, spicules inflated in middle ...... ................................................................... N. effilatus ( Boucher 1976) Platt and Warwick 1988

– Males with 17 cup-shaped precloacal supplements, spicules symmetrical ....................... ................................................................................................. N. armatus ( Gerlach 1964) Ott 1972

3. Male with a precloacal papilla and 14 button-shaped precloacal supplements .............. ....................................................................................................................... N. brevicaudatus sp. nov.

– Male with a precloacal spine and 16–18 cup-shaped supplements ..................................... ............................................................................................................................ N. decoratus Ott, 1972

Figures

Figure 3. Nannolaimoides brevicaudatus sp. nov. (a) Entire male; (b) anterior part of male, showing buccal cavity, amphid, cuticle punctations and pores; (c) posterior portion of male, showing tail, spicule, gubernaculum and precloacal supplements; (d) spicule and gubernaculum; (e) entire female; (f) female tail. Scale bars: a, e = 50 μm; b = 10 μm; c, d, f = 20 μm.

Figure 4. Nannolaimoides brevicaudatus sp. nov. (a) anterior part of male, showing outer labial and cephalic setae, buccal cavity and tooth; (b) anterior part of male, showing amphid, cuticle punctations and pores; (c) posterior portion of male, showing spicule and tail; (d) posterior portion of male, showing spicule, gubernaculum and precloacal supplements. Scale bars: a, b = 10 µm; c, d = 20 μm.