Subsphaerolaimus minor, Gagarin, Vladimir G. & Thanh, Nguyen Vu, 2015

Gagarin, Vladimir G. & Thanh, Nguyen Vu, 2015, Subsphaerolaimus minor sp. n. and Micromicron cephalatum Cobb, 1920 (Nematoda) from the Yen River Estuary of Vietnam, Zootaxa 3994 (3), pp. 396-410 : 397-402

Subsphaerolaimus minor sp. n.

( Figs 1 , 2 ; Table 1)

Type material. Holotype male, slide reference number TY 2.2.21, deposited in the Nature Museum of the Vietnamese Academy of Sciences and Technology, Hanoi, Vietnam.

Paratypes. One female, slide reference number TY 2.2.19, deposited in the Nature Museum of the Vietnamese Academy of Science and Technology. Three males and two females deposited in the nematode collection in the Institute Ecology and Biological Resources, Vietnamese Academy of Sciences and Technology, Hanoi, Vietnam. One male slide reference number TY 9.2.9; one female slide reference number TY 7.3.3.

Measurements. Table 1.

Type habitat and locality. Vietnam, Quang Ninh Province, Donghg Rhi, Yen River Estuary, mangrove forest. Latitude: 21º11.019ʹ – 21º15.901ʹ N; Longitude: 107º22.269ʹ–107º23.554ʹ E, depth 1.0– 1.5 m, silted sand, with 4.2–4.9 ‰ salinity.

Etymology. The specific epithet means “small” or “small size”.

Description. Male. Body short and slender. Cuticle and subcuticle smooth, without longitudinal ridges and transversely striated. Thickness of cuticle 0.4–0.8 µm. Somatic setae present, 6–12 µm long. Anterior body end narrowed. Labial region slightly flattened anteriorly, continuous with the body outline. Inner labial sensillae in the shape of small, poorly visible papillae. Outer labial and cephalic sensillae in the shape of short setae and united in almost one circle. Its length 3.5–4.0 µm or 23–28 % of the labial region width. Subcephalic setae 13–19 µm long and arranged in 8 groups, with 4 setae per group. Cheilostoma with ribs; gymnostoma narrow, with strongly sclerotized walls; stegostoma small, funnel-shaped. Amphidial fovea circular and occupying 23–27 % of corresponding body diameter. Amphidial fovea situated at distance 13–16 µm from anterior body end (0.9–1.1 labial region width). Pharynx muscular, cylindroid. Cardia conical, muscular, surrounded with intestinal tissue. Renette cell, canal and excretory pore not observed.

Testes paired, opposed. Anterior testis outstretched, situated to the left side of the intestine. Posterior testis reflexed, situated to the right side of the intestine. Spicules comparatively thin, bent, with small, round capitulum. Gubernaculum muff-forming (tubular), 9–11 µm long. Supplements absent. Tail slender, elongate-conical, gradually narrowing. Caudal setae present. Caudal glands and spinneret well developed. Subterminal setae 10–14 µm long.

Female. General appearance, structure of cuticle and anterior body end similar to that of male. Cuticle smooth. Labial region continuous with the body outline. Inner labial sensillae in the shape of the small papillae. Outer labial and cephalic sensillae in the shape of short setae and united in one circle. Subcephalic setae arranged in 8 groups, on 4 setae in group, 13–18 µm long. Cheilostoma with ribs; gymnostoma narrow, with sclerotized walls; stegostoma small, funnel-shaped. Amphidial fovea circular and occupying 20–25 % of corresponding body diameter. Amphidial fovea situated at distance 1.0–1.2 labial region width from anterior body end. Pharynx muscular, cylindroid. Rectum 1.0–1.2 times as long as anal body diameter.

ТABLE 1. Morphometrics of Subsphaerolaimus minor sp. n.

Reproductive system monodelphic, prodelphic; ovary situated to the left side of the intestine. Germinal zone of oogonia arranged in one or two rows; growth zone with a single row of gradually enlarging oocytes. Vagina short, curved to anterior body end. Uterus spacious, filled with small rounded spermatozoa. No postvulval uterine sac. Vulva posterior to mid-body, crescent-shaped; its lips not cuticularized and not protruding. Tail slender, elongateconical, gradually narrowing. Caudal glands and spinneret well developed. Subterminal setae 10–15 µm long.

Diagnosis. Subsphaerolaimus minor sp. n. is characterized by small body size (L = 572–725 µm), presence of six inner labial papillae; short outer labial and cephalic setae, 3.5–4.0 µm long; subcephalic setae arranged in 8 groups, with 4 setae per group, 13–18 µm long; cheilostoma with ribs; gymnostoma narrow, with strongly sclerotized walls; stegostoma small, funnel-shaped; amphidial fovea circular and situated at distance 0.9–1.2 labial region width from anterior body end; testes pair, opposed; spicules thin, with small, round capitulum; gubernaculum muff-forming (tubular); supplements absent; tail slender, elongate-conical, gradually narrowing; caudal glands and spinneret well developed; subterminal setae 10–15 µm long.

Differential diagnosis. Subsphaerolaimus minor sp. n. is the smallest species of the genus Subsphaerolaimus Lorenzen, 1978 . The new species is morphologically close to Subsphaerolaimus lamasus ( Gerlach, 1956) Lorenzen, 1978 , but differs in the shorter body (L = 572–715 µm versus L = 900 µm in S. lamasus ), comparatively shorter pharynx (b = 5.1–6.4 versus b = 4.6 in S. lamasus ) and shorter cephalic setae (3.4–4.0 µm long versus 6–9 µm long in S. lamasus ) ( Gerlach 1956).

Discussion. The genus Subsphaerolaimus was established by Lorenzen in 1978. At present, the genus contains seven valid species ( Table 3 , Fig. 3 ). Subsphaerolaimus litoralis Lorenzen, 1978 is the type species for the genus and has been found on the coast of Southern Chile. The species has medium-sized body and comparatively long subcephalic setae (25–28 µm long) ( Lorenzen 1978). S. brevicaudata Jensen, 1992 was found in a deep-sea zone of the Norwegian Sea and is characterized by its longer body (L = 2821 µm), long spicules (115 µm in length) and very short cephalic and subcephalic setae (1–3 µm) ( Jensen 1992). S. gerlachi ( Wieser, 1959) Lorenzen, 1978 collected on the coast of Washington, USA, has comparatively long cephalic setae (12 µm) ( Wieser 1959). S. lamasus has been found in mangrove forests of coastal Brazil. This species has a medium-sized body (L = 900 µm) and comparatively long cephalic setae (6–9 µm) ( Gerlach 1956). S. seticaudatus Gourbault & Boucher, 1981 has been found in deep-sea muds of the South East Atlantic and has a comparatively long body (L = 1491 µm) and relatively short pharynx (b = 3.8) ( Gourbault & Boucher 1981). S. major Nguyen & Gagarin, 2009 and S. minor sp. n. inhabit mangrove forests in river estuaries of Vietnam. S. major is characterized by comparatively long cephalic and subcephalic setae (8.5–10.0 µm and 21–38 µm long, respectively) and long spicules (46–49 µm), while S. minor sp. n. has a short body (L = 572–715 µm) and comparatively short cephalic setae (3.5–4.0) ( Nguyen & Gagarin 2009, present paper).

Author, Year Species name Sex, number L a b c of specimen

Lorenzen, 1978 S. litoralis 1♂ 800 16 4.7 6.4 1♀ 960 24 5.2 8.7 Gerlach, 1956 S. lamasus 1♂ 900 18 4.6 7.2 Author, Year Species name cʹ V c.s. subc.s. spic Lorenzen, 1978 S. litoralis 2.6 – 8 25–28 28 3.0 64 8 – –

Jensen, 1992 S. brevicauda 2.0 – 1–3 1–3 115 Wieser, 1959 S. gerlachi 3.5 – 12 36–41 26 2.7 64 – – –

Gerlach, 1956 S. lamasus 4.0 – 6– 9 11–14 30 Gourbault & Boucher, 1981 S. seticaudatus 4.9 67 4 8–10 –

Figures

FIGURE 1. Subsphaerolaimus minor sp. n. Holotype male and paratype female. A: male, entire body; B: female, entire body; C: male, head; D: female, head; E: female, vulva region; F: male, specular apparatus; G: female, tale; H: male, tail. Scale bars: A, B— 75 µm; E— 40 µm; G, H— 30 µm; C, D – 15 µm; F— 10 µm.

FIGURE 2. Subsphaerolaimus minor sp. n. Holotype male and paratype female. A: male, entire body; B: male, anterior body end; C: male, head; D: female, head; E: vulva region; F: male, cloaca region; G: male, tail, H: female, tail. Scale bars: A— 100 µm; B, E – H— 20 µm; C, D— 10 µm.

FIGURE 3. Pictorial key for valid species of genus Subsphaerolaimus.