Macrostomum shenzhenensis Wang & Wang, n. sp.
Creators: name: Wang, Lei
name: Xin, Fan
name: Fang, Chu-Yu
name: Zhang, Yu
name: Wang, An-Tai
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Platyhelminthes
Rhabditophora
Macrostomida
Macrostomidae
Macrostomum
Macrostomum shenzhenensis

description: Macrostomum shenzhenensis Wang & Wang, n. sp.
(Figs. 2–4)
Material examined. Observations were made on live and preserved specimens. Holotype (PLA– Ma 0090): one mounted specimen. Paratypes (PLA– Ma 0091–96): six serially-sectioned specimens. The type specimens were collected from a brackish lake by Lei Wang in Shenzhen City, Guangdong Province, China (22°31′87″ N, 113°58′87″ E) (see Fig. 1 for sampling location) from October to December, 2015. All specimens are deposited in IZCAS.
Etymology. The name of this new species is derived from the name of Shenzhen City, Guangdong Province, China.
Description: The body is dorsoventrally flattened and transparent under transmitted light and whitish under reflected light. The body length and width of active adult specimens is 942 ± 85 µm (n=6) and 91 ± 17 µm (n=6), respectively (length-width ratio is 10:1) (Figs. 2 A, 4A). The whole body surface is covered with cilia which are 7 ± 1.4 µm (n=6) long. The average thickness of epidermis is 2 ± 0.3 µm (n=6). The rhabdites, 13 ± 2.8 µm (n=6) long, are scattered in groups (mostly 3–7 rhabdites in each group) over the entire body surface, with higher density along the dorsal body surface. There are tufts of sensory hair that are 22 ± 2.2 µm (n=6) long, sparsely distributed on the body edge. The front end is semi-elliptic in shape. The anterior and posterior body margin have tufts of rigid cilia that are 10 ± 0.9 µm (n=6) long (Fig. 2 G). A pair of kidney-shaped eyes is located at the anterior 15% of the body and the distance between the two eyes is 16 ± 3.6 µm (n=6). The mouth is 83 ± 10.0 µm (n=6) long. The pharynx is ventrally surrounded by a number of rod-shaped pharyngeal glands (Fig. 3 B). The width of the empty intestine is 3 ± 0.4 µm (n=6). Its tail is rounded, with numerous adhesive glands located at the posterior end of the body (Fig. 2 G).
The male reproductive system consists of a pair of testes and vasa deferentia, a false vesicula seminalis, a vesicula seminalis, a vesicula granulorum, a penis stylet and a male gonopore (Figs. 2 B–C, 3C–G, 4B–C). The testis, 99 ± 14.4 µm (n=3) long, is elongated oval shaped alongside the anterior part of the intestine and has a smooth surface. The oval-shaped false vesicula seminalis lies posteriorly to the female antrum and connects to the oval-shaped vesicula seminalis on its right lower side. The vesicula granulorum is also oval shaped, and connects to the vesicula seminalis on its right lower side, and around half of the vesicula granulorum is enclosed by the proximal end of the ‘J-shaped’ penis stylet. The lengths of the curved line (marked as ‘a’) and straight line (marked as ‘b’) between the proximal and distal ends of the stylet are 59 ± 4.5 µm (n=8) and 64 ± 3.6 µm (n=8), respectively (Fig. 4 C). The diameter of the proximal end is slightly larger than the distal end, while it remains almost unchanged in the distal 25% of the stylet. The proximal and distal parts of the penis stylet are 13 ± 1.1 µm (n=8) and 2 ± 0.6 µm (n=8) (marked as ‘d’) wide respectively (Figs. 4 C-D). The stylet bends at 82% of its length and forms a bending angle of 111 ± 5.0° (n=8) (Figs. 2 D–E). The asymmetrical thickening of the penis stylet ′s distal opening is torus shaped (Figs. 2 F, 4D). External (marked as ‘c’) and internal (marked as ‘d’) diameters of the distal opening are 4 ± 0.8 µm (n=8) and 2 ± 0.6 µm (n=8) (Fig. 4 D).
The mature sperm are 111 ± 1.7 µm (n=8) long when swimming (Figs. 2 J, 4E). The length of feeler, body and shaft of the sperm are 25 ± 1.9 µm, 22 ± 1.1 µm and 64 ± 2.2 µm (n=8), respectively. Diameters of the three parts are 0.6 ± 0.2 µm, 2.0 ± 0.7 µm and 1.3 ± 0.2 µm (n=8). A pair of bristles, 17 ± 1.0 µm (n=6) long, is on the sperm body. Four to seven brushes, 6 ± 0.6 µm (n=8) long, can be observed at the posterior end of the shaft (Figs. 2 H–J). However, in immature sperm, the posterior part of the shaft is swollen and does not show any brushes (Fig. 2 I).
The female reproductive system consists of a pair of ovaries and oviducts, a female antrum and a female gonopore (Figs. 2 A–B). The ovaries, 70 ± 2.1 µm (n=3) long, are located at the posterior 50% of the intestine. The female antrum is located at the posterior 20% position of the body, and contains plenty of sperm in mature individuals. The female gonopore opens ventrally at the posterior part of female antrum. Moreover, the female gonopore is surrounded by a great halo of cement glands (Figs. 2 B, 3A).
Remarks. Comparison of the penis stylets of M. shenzhenensis n. sp. and four similar species previouslydescribed within the genus Macrostomum is shown in TABLE 1. They have following characteristics in common: 1) stylet is a narrow tube with a slightly wider proximal opening and 2) the distal opening of the stylet is blunt, with obvious thickenings of the opening ′s wall. However, each of these four species is obviously different from M. shenzhenensis n. sp. as to the bending angle and position of bending in stylet. In M. reynoldsoni, its penis stylet's length is much longer than that of M. shenzhenensis n. sp. and the bending angle is less than 90°. In M. poznaniense, the length of its stylet is shorter than that of M. shenzhenensis n. sp. The bending angle is larger than 120°, while diameter of proximal opening is smaller than that of M. shenzhenensis n. sp ..
* Measurement based on images and scales from the references.
M. lignano and M. flexum are most similar to M. shenzhenensis n. sp. in the overall morphology of the stylets. M. flexum and M. shenzhenensis n. sp. have stylets of comparable lengths and with comparable diameters of the stylet's proximal and distal openings. However, the penis stylet of M. flexum bends over 150° at 77% of its length, which is much larger than the bending angle of M. shenzhenensis n. sp .. Moreover, the distal opening of the stylet of M. flexum is bulbously thickened, which differs from the annularly thickening of M. shenzhenensis n. sp.. M.
lignano and M. shenzhenensis n. sp. are similar in ratio of stylet length to diameter of basal opening/distal opening (2 and 13 in M. shenzhenensis n. sp.; 5 and 14 in M. lignano). They are similar in the position of curve in stylet (83% position in M. lignano; 82% position in M. shenzhenensis n. sp.). Nevertheless, bending angle of its stylet (>120°) is still larger than that of M. shenzhenensis n. sp. (~114°). In addition, the wall of the distal opening is not as thick as that of M. shenzhenensis n. sp.. In summary, based on the morphology characteristics of penis stylet, it is evident that M. shenzhenensis n. sp. is a new species within the genus Macrostomum.
description: Published as part of Wang, Lei, Xin, Fan, Fang, Chu-Yu, Zhang, Yu & Wang, An-Tai, 2017, Two new brackish-water species of Macrostomum (Platyhelminthes, Macrostomida) from mangrove wetland in southern China, pp. 107-124 in Zootaxa 4276 (1) on pages 109-113, DOI: 10.11646/zootaxa.4276.1.5, http://zenodo.org/record/804693