Dugesia ancoraria Zhu & Wang, 2024

Zhu, Ying, Huang, JiaJie, Sluys, Ronald, Liu, Yi, Sun, Ting, Wang, An-Tai & Zhang, Yu, 2024, Integrative description of a new species of Dugesia (Platyhelminthes, Tricladida, Dugesiidae) from southern China, with its complete mitogenome and a biogeographic evaluation, Zoosystematics and Evolution 100 (1), pp. 167-182 : 167

Dugesia ancoraria Zhu & Wang sp. nov.

Material examined.

Holotype: PLA-0251, a narrow artificial canal of Wenshan lake , Shenzhen city, Guangdong Province, China, 22°31'55"N, 113°56'21"E, 10 May 2021, coll. MY Xia and co-workers, sagittal sections on 14 slides.

Paratypes: PLA-0252, ibid., sagittal sections on 12 slides; PLA-0253, ibid., transverse sections on 35 slides; RMNH.VER.21525.1, ibid., sagittal sections on 12 slides.

Habitat.

Specimens were collected from a narrow artificial canal running from Wenshan lake (22°31'55"N, 113°56'21"E), which is located in Shenzhen city, Guangdong Province, China (Fig. 1A ). The animals were collected from Cladophora algae, as well as the stone wall of the canal, which had a water depth of 20-30 cm; water temperature was about 23 °C. Thirty specimens were collected, none of which was sexually mature. However, after six months of rearing under laboratory conditions, about 20 specimens eventually attained sexual maturity.

Diagnosis.

Dugesia ancoraria is characterised by the following characters: highly asymmetrical penis papilla, provided with a hunchback-like dorsal bump; vasa deferentia opening symmetrically into the mid-lateral section of the more or less ellipsoidal seminal vesicle, which may give rise to a narrow dorsal extension; long and narrow duct connecting seminal vesicle with small diaphragm; ejaculatory duct with a subterminal opening through the ventral surface of the penis papilla; asymmetrical oviducal openings, with the right oviduct opening into a section of the bursal canal that bends ventrally to communicate with the common atrium; the left oviduct opens into the bursal canal at the point where the latter meets the common atrium.

Etymology.

The specific epithet is derived from Latin adjective ancorarius, of the anchor, and alludes to the penis papilla, which has a hunchback-shape, reminiscent of an anchor, more or less.

Description.

Sexualized specimens measured 8.43-9.11 mm in length and 1.13-1.18 mm in width (n = 4; Fig. 5A, B ). Head of low triangular shape with blunt auricles. At the level of the auricles there is a pair of black, bean-shaped eyes, located in pigment-free areas. The distance between the eyes and the lateral body margin is about 0.36-0.46 mm, while the size of the eyecups varies between 210-230 μm. Each eyecup contains numerous retinal cells.

The ground colour of the dorsal surface is brown, dotted with dark brown and white specks; ventral surface much paler than dorsal surface; the body margin is pale (Fig. 5A, B ).

The cylindrical pharynx is positioned at about 1/2 of the body and measures about 1/5 of the total body length; the mouth opening is situated at the posterior end of the pharyngeal pocket. The musculature of the pharynx consists of an outer, subepithelial layer of circular muscle, followed by a layer of longitudinal muscle, while the inner musculature is composed of a thick, subepithelial layer of circular muscle, followed by 2-3 layers of longitudinal muscle. The gonopore is situated at about 1/5 of the length of the body, as measured from the posterior body margin (Fig. 5D ).

The globular ovaries are located at 1/6 - 1/7 of the distance between the brain and the root of pharynx. From the ovaries, the nucleated oviducts run ventrally in a caudal direction and open separately and asymmetrically into the female reproductive apparatus. Posterior to the gonopore, the right oviduct turns antero-medially and then opens into a section of the bursal canal that bends ventrally to communicate with the common atrium. The left oviduct opens into the bursal canal at the point where the latter meets the common atrium. (Figs 6A , 9B ).

A large sac-shaped copulatory bursa is situated immediately behind the pharyngeal pocket and occupies the entire dorso-ventral space; it is lined with a layer of vacuolated, nucleated cells (Figs 6B , 9B ). From the bursa, the bursal canal runs in a caudal direction dorso-laterally to the male copulatory apparatus. At the level of the gonopore, the bursal canal curves rather sharply downwards, thus giving rise to a more or less vertically oriented section that opens through the dorsal wall of the common atrium (Figs 6C , 9B ).

The bursal canal is lined by a nucleated, columnar glandular epithelium, which is underlain with a layer of longitudinal muscles, followed by 1-4 layers of circular muscles. Along the ventral coat of muscle, ectal reinforcement is present in the form of a single layer of longitudinal muscle running from about the opening of the canal into the common atrium to about 1/3 of the length of the bursal canal (Fig. 9B ). Shell glands discharge their cyanophil secretion into the most ventral section of the vertically running portion of the bursal canal, with some glands even discharging into the common atrium (Figs 6B, C , 9B ).

The large, near-globular testicular follicles are situated dorsally and extend posteriorly from a short distance behind the brain to well beyond the copulatory apparatus. The male atrium comprises most of the dorso-ventral space of the body (Figs 6A , 9A, B ). The large and oval-shaped penis bulb is composed of intermingled longitudinal and circular muscle fibres. The penis papilla has a more or less oblique, postero-ventral orientation or even a vertical orientation, and has a striking shape (Figs 6A , 9A ). The papilla is markedly asymmetrical as a result of the course of ejaculatory duct, which opens to the exterior through the postero-ventral wall of the penis papilla. Furthermore, near its root, the papilla has a dorsal bump, which gives it a hunchback appearance (Figs 6A , 9A ). The degree of development of this dorsal bump differs between specimens. In the holotype it is highly developed (Fig. 6A ), while in paratype PLA-0104 it is somewhat smaller, albeit still well-developed (Fig. 8A ), but in paratype PLA-0102 the bump is practically absent (Fig. 7A ). In addition, the asymmetrical appearance of the penis papilla is enhanced by the fact that the distal portion of the dorsal lip of the papilla gives rise to another bulge, which may be swollen or drawn-out to a greater or lesser extent. In paratype RMNH.VER.21525.1, it is a rather long-drawn bulge (Fig. 8A ), whereas in the holotype and paratype PLA-0102 it is more rounded (Fig. 7A ). The papilla is covered by a thin, nucleated epithelium, which is underlain with a well-developed, subepithelial layer of circular muscle, followed by a layer of longitudinal muscle at the ventral root.

The vasa deferentia have expanded to form spermiducal vesicles that are packed with sperm. At the level of the penis bulb, the ducts recurve, while decreasing in diameter, run postero-medially for some distance and, thereafter, recurve anteriad before opening separately into the mid-lateral portion of the seminal vesicle (Figs 6A , 9A, B ). The vesicle has a more or less ellipsoidal shape, while its dorsal wall may form a narrow extension, which was present in all specimens examined, excepting paratype RMNH.VER.21525.1. The seminal vesicle is lined by a ciliated, nucleated epithelium. A long and narrow duct connects the seminal vesicle with the small diaphragm, which communicates with the ejaculatory duct. The diaphragm receives the abundant secretion of erythrophil penial glands. From the diaphragm, the ejaculatory duct curves strongly postero-ventrally to open subterminally through the ventral epithelium of the penis papilla, thus giving rise to a highly asymmetrical papilla with a large dorsal lip and a small ventral lip (Figs 6A , 9A ). Particularly the blunt tip of the dorsal lip of the penis papilla is penetrated by the numerous openings of orange-staining glands.

The male atrium is lined by a nucleated epithelium. The dorsal part of the male atrium is surrounded by a layer of circular muscle, followed by 1-2 layers of longitudinal muscle, while a subepithelial layer of circular muscle, followed by a layer of longitudinal muscle constitutes the musculature on the ventral part of the atrium. The male atrium communicates with the common atrium via a broad opening. The common atrium is lined with a nucleated epithelium, which is underlain by 2-3 layers of circular muscle (Figs 6A , 9 ).

Figures

Figure 1. Locality and habitat of Dugesia ancoraria. A. Sampling locality in Guangdong Province, China; B, C. Habitat at sampling locality.

Figure 5. External morphology of Dugesia ancoraria. A. Living sexual animal in dorsal view; B. Living sexual animal in ventral view; C. Anterior end, dorsal view; D. Ventral view of rear end, showing pharynx, mouth and gonopore. Scale bars: 500 μm.

Figure 6. Dugesia ancoraria, holotype PLA- 0101, sagittal sections, anterior to the right. A. Photomicrograph showing copulatory bursa, ejaculatory duct, penis papilla, and seminal vesicle; B. Photomicrograph showing copulatory bursa, bursal canal, and gonopore; C. Photomicrograph showing copulatory bursa, and bursal canal. Scale bars: 100 μm.

Figure 7. Dugesia ancoraria, paratype PLA- 0102, sagittal sections. A. Photomicrograph showing ejaculatory duct, penis papilla, and seminal vesicle; B. Photomicrograph showing copulatory bursa, bursal canal, and gonopore. Scale bars: 100 μm.

Figure 8. Dugesia ancoraria, paratype RMNH. VER. 21525.1, sagittal sections. A. Photomicrograph showing ejaculatory duct, penis papilla, and seminal vesicle; B. Photomicrograph showing copulatory bursa, common atrium, and gonopore; C. Photomicrograph showing copulatory bursa, and bursal canal. Scale bars: 100 μm.

Figure 9. Dugesia ancoraria, Sagittal reconstruction of the copulatory apparatus of the holotype. A. Male copulatory apparatus; B. Female copulatory apparatus. Scale bars: 100 μm.