Theristus coralis, 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 : 402-405

Genus Theristus Bastian, 1865 Theristus coralis sp. n.

( Figs. 1 , 2 ; Table 1)

https://www.zoobank.org/NomenclaturalActs/ 9D55AE0E- A48A-4B01-8421-30A460914D30

Type material. Holotype male, inventory slide number Tso 1, 3 deposited in the Vietnam National Museum of Nature, Vietnam Academy of Science and Technology (Hanoi, Vietnam).

Paratypes. 10 ♂, 8 ♀ 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 1.

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 : 2–8 m. Water salinity: 2.4–3.5 ‰.

Etymology. The specific epithet means “coral”.

Description. Male. Body comparatively large, slender. Cuticle finely annulated, thin. Head end narrowed. Body width at the posterior end of the pharynx exceeds labial region width in 2.1–2.6 times. Somatic setae not observed. Labia relatively high, labial region not separated from body. Six internal labial sensillae in the shape of papillae. Six outer labial sensillae and four cephalic sensillae in the shape of setae. Outer labial setae 14–17 µm long, 61– 70% of labial region width. Cephalic setae 10– 12 µm long. Cheilostoma spacious, its walls sclerotized. Pharyngostoma also spacious, with sclerotized walls. Teeth and onchae absent in stoma. The fovea of amphids are circular, 10–12 µm diameter (50–55% of the body width at this level) and located at distance of 20–25 µm from anterior end of body. Pharynx is muscular only slightly widening towards its base. Cardia small, protrudes into the lumen of middle intestine. Around cardia there are three large, oval formations with granular structure (glands?). Renette and its excretory pore not found.

Testes two, opposed. Anterior testis straight, located to the left of the intestine. Posterior testis curved, short, barely visible. Spicules thin, curved, with poorly expressed head. Spicules about 1.7 times as long as body cloacal diameter. Gubernaculum grooved, like a “sleeve”, encloses distal ends of spicules. Distal end gubernaculum armed well sclerotized

Table 1 Morphometrics of Theristus coralis sp. n. (All measurements are in µm, expert for the rations a, b, c, cʹ, V) ТабΛица 1 Морфометрия Theristus coralis sp. n. (Все размеры указаны в мкм ΑΛя соотношений a, b, c, c ʹ, V)

claw-shape formation. Precloacal ventromedial supplement absent. Tail elongate-conical. Caudal glands hardly visible. Spinneret present. Subterminal setae absent.

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 left of intestine. Vulva postequatorial in the form of transversal slit. Vulva lips not sclerotized and do not protrude beyond the contours of body. Vagina relatively short, thin-walled and stopping towards the posterior body end. Uterus filled with numerous sperm. In two females two eggs, 67–70x35–40 µm size. Posterior uterus sack present, 60–82 µm long. The tail elongate-conical, gradually tapering. Caudal glands and spinneret present. Subterminal setae absent.

Differential diagnosis. Theristus coralis sp. n. is included in the flevensis group of the genus Theristus Bastian, 1865 , which includes 13 valid species ( Nguyen Dinh Tu, Gagarin 2017). New species is morphologically close to Th. macroflevensis Gerlach, 1954 and Th. metaflevensis Gerlach, 1955 but differs from both species by the presence of cardial glands and the posterior uterus sack in females ( Nguyen Dinh Tu, Gagarin 2017). In addition, it differs from the first by the shorter body (L = 1404–1740 µm vs L = 1797– 1865 µm in Th. macroflevensis ), comparatively longer pharynx (b = 4.4–5.5 vs b = 5.7–6.5 in Th. macroflevensis ), less slender tail (c ʹ = 3.9–5.6 vs c ʹ = 5.5–6.6 in Th. macroflevensis ), closer to anterior body end located vulva (V = 65–69% vs V = 74–76% in Th. macroflevensis ) and shorter gubernaculum (24–29 µm long vs 35 µm long in Th. macroflevensis ( Gerlach 1954) . Th. coralis sp. n. differs from Th. metaflevensis Gerlach, 1955 by the longer pharynx (b = 4.4–5.5 vs b = 6.9–7.7 in Th. metaflevensis ), comparatively shorter tail (c = 7.9–9.6 vs c = 6.7–7.5 in Th. metaflevensis ), closer to anterior body end located vulva (V = 65–69% vs V = 87% in Th. metaflevensis ), longer outer labial setae (13–17 µm long vs 11–12 µm long in Th. metaflevensis ) and shorter gubernaculum (24–29 µm long vs 42 µm long in Th. metaflevensis ) ( Gerlach 1955).

Figures

Fig 1. Theristus coralis sp. n., holotype male and paratypes female: A — male head; B — anterior body of male; C — vulva region; D — spicular apparatus; E — posterior end of male; F — posterior end of female. Scale bars: A — 20 µm; D — 40 µm; B, C, E, F — 70 µm

Fig 2. Theristus coralis sp. n. Holotype male and paratype female. A — male, entire body; B — female, entire body; C — male, head; D — male, head; E — male, anterior body end; F — male, cloaca region; G — female, vulva region; H — male, posterior body end; I — male, posterior body end; J — female, tail terminus. Scale bars: B — 200 µm; A — 100 µm; E, G, H, I — 50 µm; C, D, F, J — 10 µm Рис. 2. Theristus coralis sp. n., гоΛотип, самец и паратип, самка: А — самец, общий виΑ; B — самка, общийвиΑ; С —самец, гоΛова;D —самец, гоΛова;Е — самец, переΑнийконец теΛа; F — самец, обΛасть кΛоаки; G — самка, обΛасть вуΛьвы; H — самец, заΑний конец теΛа; I — самец, заΑний конец теΛа; J — самка, конец хвоста. Масштабные Λинейки: B — 200 мкм; А — 100 мкм; E, G, H, I — 50 мкм; C, D, F, J — 10 мкм