Thalassomonhystera gracilima, Long & Thu & Gagarin & Tu, 2023

Long, Phan Ke, Thu, Nguyen Thi, Gagarin, Vladimir G. & Tu, Nguyen Dinh, 2023, Theristus coralis sp. n. and Thalassomonhystera gracilima sp. n. (Nematoda, Monhysterida) from coral reef off the coast of Vietnam, Amurian Zoological Journal XV (2), pp. 401-410 : 406-409

Genus Thalassomonhystera Jacobs, 1987 Thalassomonhystera gracilima sp. n.

( Figs. 3 , 4 ; Table 2)

https://www.zoobank.org/ NomenclaturalActs/ 0D822557-EFDE-4D73-9252- E0C28E74274D

Type material. Holotype male, inventory slide number MSS-sh, 23 deposited in the Vietnam National Museum of Nature, Vietnam Academy of Science and Technology (Hanoi, Vietnam).

Paratypes. 10 ♂, 10 ♀ deposited in the collection of nematodes of the Institute of Ecology and Biological Resources of the Vietnam Academy of Sciences and Technology (Hanoi, Vietnam) .

Measurements. Table 2.

Type locality. South China Sea, shallow area of the coast of Vietnam. Coral reef from Cam Ranh , Khanh Hoa Province. Coordinates : 12 ° 8ʹ33ʹʹN-12 ° 25ʹ18ʹʹN, 109 ° 7ʹ16ʹʹE-109 ° 14ʹ30ʹʹE. Depth : 2–5 m. Water salinity: 2.4–3.5 ‰.

Etymology. The specific epithet means “graceful”.

Description. Male. Body comparatively long and thin. Head end narrowed. Cuticle smooth under light microscope. Somatic setae not observed. Labia relatively high. Labial region not separated from body. Six internal labial sensila in the shape of papillae. Six outer labial sensila and four cephalic sensila in the shape of setae. Outer labial setae 12–16 µm long (65–80% of labial region width). Cephalic setae 7–10 µm long. Amphidial fovea circular, 9–11 µm diameter and situated at distance of 33–39 µm from anterior body end (1.8–2.1 labial region width). Cheilostoma spacious, with sclerotized walls. Pharyngostoma consists of two sections: anterior section wide, posterior section narrowed, in the form of tube. Teeth and onchiae in stoma absent. Pharynx slender, cylindroid, slightly widened at the posterior end. Cardia small, triangular, protrudes into the lumen of the intestine. Around cardia there are three oval granular glands. Renette and its excretory pore not observed.

Testis one, outstretched, situated to the right of the intestine. Spicules long, thin, arculate 3.0–3.4 times as long as cloacal body diameter. Distal end of spicules hooked. Gubernaculum and precloacal supplements absent. Tail long, with proximal conical and distal thin, cylindrical portions gradually going over into one another. Distal tail portion 1.3– 1.6 times as large as proximal portion. Tail tip with 2–3 subtermal setae. Caudal glands and spinerette present.

Female. General morphology similar to that of males. Structure of cuticle and anterior body end as in males. Ovary single, anterior, straight, relatively long, and located to rough of intestine. Vulva postequatorial, in the form of transverse slit. Vulva lips not sclerotized. Vagina comparatively short, with thin walls and stopping to wards to posterior body end. Uterus spacious, filled with numerous sperm. Postvulvar oval cell present. Tail long, with proximal conical and distal thin, cylindrical portions. Distal tail portion 3.2–3.6 times as large as proximal portion. Tail tip with 2–3 subterminal setae. Caudal glands and spinneret present.

Differential diagnosis. Th. gracilima sp. n. at structure specular apparatus (absence of gubernaculum) is close to Th. tasmaniensis ( Allgen, 1927) , found in coast zone of Tasmania, but differs from it by a longer and thinner body (L = 1026–1335 µm, a = 44–56 vs L = 610–785, a = 24–37 in Th. tasmaniensis ), a more slender tail in females (♀♀ c ʹ = 10.0– 12.2 vs ♀♀ c ʹ = 6.0– 6.5 in Th. tasmaniensis ), longer spicules with a different structure (spicules 51–57 µm long, with hooked at distal part vs 35 µm long, its distal part straight) and a different structure of pharyngostoma (divided into two section vs pharyngostoma whole, funnel-shaped) ( Allgen 1927).

Table 2 Morphometrics of Thalassomonhystera gracilima sp. n. (All measurements are in µm, expert for the rations a, b, c, c ʹ, V) ТабΛица 2 Морфометрия Thalassomonhystera gracilima sp. n. (Все размеры указаны в мкм ΑΛя соотношений a, b, c, c ʹ, V)

Figures

Fig 3. Thalassomonhystera gracilima sp. n. Holotype male and paratypes female. A — male head; B — male, anterior body end; C — female, vulva region; D — male, spicular apparatus; E — female, posterior body end; F — male, posterior body end. Scale bars: A–D — 15 µm; C, E, F — 30 µm; B — 50 µm Рис. 3. Thalassomonhystera gracillima sp. n., гоΛотип, самец и паратип, самка: A — самец, гоΛова; B — самец, переΑний конец теΛа; C — самка, обΛасть вуΛьвы; D — самец, спикуΛярный аппарат; E — самка, заΑний конец теΛа; F — самец, заΑний конец теΛа. ШкаΛы: A–D — 15 мкм; C, E, F — 30 мкм; B — 50 мкм

Fig 4. Thalassomonhystera gracilima sp. n. Holotype male and paratypes female. A — male, entire body; B — female, entire body; C, D — male, head; E — female, head; F — male, anterior body end; G — male, cardia region; H — male, cloaca region; I — female, vulva region; J — male, posterior body end; K — female, posterior body end; L — female, tail terminus. Scale bars: A, B — 100 µm; F, I, K — 50 µm; C, D, E, G, H, I, L — 10 µm Рис. 4. Thalassomonhystera gracilima sp. n., гоΛотип, самец и паратип, самка: A — самец, общий виΑ; B — самка, общий виΑ; C — самка, гоΛова; E — самка, гоΛова; F — самец, переΑняя часть теΛа; G — самец, обΛасть карΑии; H — самец, обΛасть кΛоаки; I — самка, обΛасть вуΛьвы; J — самец, заΑний конец теΛа; K — самка, заΑний конец теΛа; L — самка, хвостовой конец. ШкаΛы: A, B — 100 мм; F, I, K — 50 мм; C, D, E, G, H, I, L — 10 мм