Thalassomonhystera tortospicula, Meng & Liang & Wang, 2025

Meng, Zhiyu, Liang, Huixin & Wang, Chunming, 2025, Phylogenetic analysis within Monhysteridae and Thoracostomopsidae based on rDNA sequences and two new species from the Yellow Sea, China, Zoosystematics and Evolution 101 (3), pp. 1339-1358 : 1339-1358

Thalassomonhystera tortospicula sp. nov.

Figs 1 , 2 , Table 3

Type material.

Four males and three females were collected from Station CDLJ in March 2023. Holotype: • ♂ 1 on slide number 23 CDLJ 4-4 , paratypes: • m # 2, m # 3, m # 4 and f # 1 on 23 CDLJ 4-1 ; f # 2 on 23 CDLJ 4-3 , f # 3 on 23 CDLJ 4-4 .

Type locality and habitat.

All specimens were collected from Changdao Island, Shandong Province, China. 37°54'N, 120°45'E (LJ), 0–2 cm sediment depth, sandy sediment.

Etymology.

The specific name refers to spicules shape jointed.

Measurement.

All measurement data can be found in Table 3 .

Description.

Male. Body medium-sized, anterior and posterior body ends narrowed. Cuticle finely striated. Inner labial sensillae papilliform. Six outer labial setae and four head setae short and in one circle. Cervical setae not found. Amphidial fovea small and circular (28–33 % c. b. d.), situated at the end of buccal cavity. Cheilostoma extensive with sclerotized walls. Buccal cavity funnel-shaped. The pharynx slender, muscular, slightly expanding to its base. Nerve ring at 49–63 % of pharynx length. Cardia muscular and inverse triangular-shaped, protruding into the lumen of the intestine. Excretory gland positioned posterior to the pharynx region and excretory pore posterior to nerve ring.

Single testis outstretched and located to the right of the intestine. Spicules paired and strongly curved, proximal end not cephalated and twisted at one-third from proximal end, distal end tapered, 1.5–1.6 cloacal body diameters in length. Gubernaculum with dorsal-caudal directed apophysis, 0.36–0.42 cloacal body diameters. Tail conical-cylindrical, cylindrical portion 27.6–31.2 %. Three caudal glands in line with a common secretory pore.

Female. Similar to males in most respects except amphidial fovea smaller (20.6 % – 21.9 %). Ovary outstretched and prodelphic, located to the right of intestine. Vulva located at posterior portion of the body (62–64 % of the body length from the anterior end), 212–238 µm from anus.

Diagnosis.

Thalassomonhystera tortospicula sp. nov. is characterized by body medium sized, outer and labial setae short, amphidial fovea positioned at the buccal cavity, spicules twisted, gubernaculum with dorsal-caudal directed apophysis, tail conical-cylindrical.

The new species differs from other species of Thalassomonhystera in the spicules anterior twisted. Thalassomonhystera tortospicula sp. nov. is similar to Thalassomonhystera attenuata Jacobs, 1987 , Thalassomonhystera lepta Gagarin & Nguyen Dinh Tu, 2021 , Thalassomonhystera parva ( Bastian, 1865) Jacobs, 1987 , Thalassomonhystera siamensis Kito & Aryuthaka, 1998 with amphidial fovea position, but differs from T. attenuata in spicules length (1.5–1.6 cloacal body diameters vs. 1.1 cloacal body diameters) and gubernaculum length (9–11 µm vs. 7 µm) ( Jacobs 1987); differs from T. lepta in outer labial setae length (4 µm vs. 6.5–8.5 µm) and tail shape (conical-cylindrical vs. elongated conical) (Gagarin and Tu 2021); differs from T. parva in absence of cervical setae (present in T. parva ), secretory pore position (posterior to nerve ring vs. anterior to nerve ring) ( Jacobs 1987); differs from T. siamensis in body length (883–1039 µm vs. 497–655 µm), absence of cervical setae (present in T. siamensis ), and gubernaculum apophysis shape (straight vs. curved) ( Kito and Aryuthaka 1998).

Figures

Figure 1. Thalassomonhystera tortospicula sp. nov. A. Lateral view of the male anterior region; B. Lateral view of the female anterior region; C. Lateral view of the female posterior body; D. Lateral view of the male entire body; E. Lateral view of the female entire body; F. Lateral view of the male posterior body, showing the tail region; G. Spicules and gubernaculum. Scale bars: 30 µm (A, B, C, F); 100 µm (D, E); 20 µm (G).

Figure 2. Thalassomonhystera tortospicula sp. nov. A. Lateral view of the male anterior region, showing amphidial fovea; B. Lateral view of the male anterior region, showing cephalic setae and buccal cavity; C. Lateral view of the male posterior region, showing spicules; D. Lateral view of the male posterior body, showing gubernaculum. Scale bars: 20 µm (A – D).