Macrostomum heyuanensis Wang & Sun

Sun, Ting, Zhang, Lv, Wang, An-Tai & Zhang, Yu, 2015, Three new species of freshwater Macrostomum (Platyhelminthes, Macrostomida) from southern China, Zootaxa 4012 (1), pp. 120-134 : 121-125

Macrostomum heyuanensis Wang & Sun , n. sp.

( Figs. 1–6 )

Material examined. Holotype (PLA-Ma0001): permanent slides of longitudinal section. Paratype (PLA-Ma002- 3): permanent slides of longitudinal and horizontal sections. Paratype (PLA-Ma004-12): batches of animals in 10% formaldehyde. Paratype (PLA-Ma0013-20): batches of animals in ethanol. All specimens are deposited in IZCAS. This new species was collected from a country brook in Dongyuan County, Heyuan City, Guangdong Province, China (23°58'38.95"N, 115° 2'43.75"E) in February 2014, at the water depth of about 20 cm. Habitat landform is mountainous basin. The ambient water is limpid and the river bed is sandy. There are aquatic plants, shrimp, snails, zooplankton and other aquatic invertebrates in the water. Farmlands are surrounded by mountains. There are no factories distributed in the upstream. Specimens were collected in March, April and July of 2014, respectively. The number of Macrostomum specimens decreased radically during the sampling period in the sampling site, mainly due to the interference of agricultural activities at that time. Rhabdocoela, Tricladida, Prolecithophora and other Turbellarians were also found from the water samples. The country brook flows into Heyuan river section, Dongjiang. However, no turbellarian was found in this river section.

Etymology. The name of this new species is originated from the name of Heyuan City, Guangdong Province, China.

Description. The body is flat, transparent and milk-white in color. The length and width of its body is 1086 ± 272.5 µm (n = 3) and 240 ± 54.5 Μm (n = 3), respectively. Its head is slightly narrow and semi-elliptic ( Fig. 3 A, Fig.4 A). The body surface has no pigments, but has dense cilia (c). The body edge has tufts of rigid cilia (rc). The dorsal part of its body is densely covered with rhabdites. There are a pair of granule-shaped eyes (e) at anterior 1/6 position of the body. The oblong-shaped pharynx (p) is located posterior to the eyes. Both sides of the pharynx (p) are interconnected with pharyngeal glands (pg) ( Figs. 2 A–D & 3A).

Macrostomum heyuanensis n. sp. is hermaphroditic. For male reproductive system, a pair of testes (t) are located at both sides of the anterior 1/3 position of intestine (in). These rod-like organs have smooth surface and are not lobulated ( Fig. 2 E). When adult M. heyuanensis is swimming or crawling, the false vesicula seminalis (fvs), vesicula seminalis (vs) and vesicula granulorum (vg) are arranged in a “U” shape. The spheroidshaped false vesicula seminalis (fvs) is located at the mid-ventral line at the posterior margin of female antrum (fa), and has a short ductus connecting vesicula seminalis (vs) at the right posterior side. Vesicula seminalis (vs) is spherical shaped and located at the right edge posterior 2/5 position of false vesicula seminalis (fvs). The anterior part of vesicula seminalis (vs) connects the vesicula granulorum (vg) via a short ductus. The vesicula granulorum (vg) is located at the right side of anterior 3/5 position of false vesicula seminalis (fvs); its anterior part connects the base of penis stylet (ps) and partially penetrates into the penis stylet (ps) tube ( Fig. 2 F). The penis stylet bends 108° leftwards at its middle part, and then bends backwards besides the distal opening. The distal opening is located terminally and points at the male gonopore (mg) ( Figs. 3 G–H, 4A–C). The curved-line (marked as ‘a’) and straightline (marked as ‘b’) distances between the base and distal end of penis stylet (ps) are 103 ± 12 µm (n = 3,) and 86 ± 11 µm (n = 3) ( Fig. 4 D). Diameter of the base of penis stylet (ps) is 14 ± 2.3 Μm (n = 3) and becomes thinner afterwards. The penis stylet (ps) is slightly swollen at its 1/4 posterior position. Diameter of distal opening of penis stylet (ps) is 3.2 ± 0.14 µm (n = 3). The wall is thicker at the distal part as compared with other parts of stylet (ps) ( Figs. 2 H; Figs. 4 C–D). A pair of ovaries (o) is located at both sides of intestine (in). Female antrum (fa) situates posterior to intestine (in) on the ventral side, and is surrounded by cement glands (cg) ( Fig. 4 D). Female antrum (fa) usually contains sperm, but sometimes ovicells. Each sperm contains a head and a tail region ( Figs. 2 I, 4E).

Phylogenetic analysis. The phylogenetic trees generated by maximum likelihood (ML) and neighbor joining (NJ) methods are shown in Figs 5 & 6 . Both results indicated that the 18S rDNA gene sequences of M. heyuanensis n. sp. 1–3 clustered together. Notably, M. heyuanensis n. sp. formed a well-supported clade with the other 7 species of Macrostomum , including M. hystrix ( FJ715303 ), M. tuba ( FJ715300 ), M. quiritum ( FJ715299 ), M. balticum ( FJ715310 ), M. longituba ( FJ715309 ), M. hystricinum ( FJ715311 ), and M. pusillum ( FJ715314 ). The 18S rDNA of M. heyuanensis n. sp. was much closer to the one of Bradynectes sterreri ( FJ715298 ) than to those of Dolichomacrostomum uniporum ( FJ715295 ), Microstomum lineare ( KC 869791 ), and Microstomum papillosum ( FJ715296 ), which are representatives of the families Dolichomacrostomidae and Microstomidae , respectively.

Remarks. There are 6 species similar to M. heyuanensis n. sp. identified in this study. 1) In M. extraculum Ax & Armonies, 1990 the penis stylet (ps) istubular, 68~72 Μm in length and rotates at its distal end. The diameters of base and distal opening are 18~22 Μm and 3 Μm, respectively. The lower edge of the distal opening is thicker than other parts of penis stylet (ps). 2) In M. retortum Papi, 1951 , the length of penis stylet (ps) is 138 Μm, and the distal opening is in a helix shape. The diameters of base and distal opening of the tube are 20 Μm and 3.5 Μm, respectively, and the straight-line distance between the proximal and distal end is 127 Μm. 3) M. bellebaruchae Ax, 2008 , the posterior end of penis stylet (ps) has 2 similar helixes, and the edge of distal opening is not thickened. The straight-line distance between the base and distal end is approximately 56 Μm. 4) In M. leptos An der Lan, 1939, its penis stylet is in bow-shaped with a 110° angle. The distal opening is helix-shaped and is not thickened. 5) In M. lewisi Ferguson, 1939 , its penis stylet (ps) is 104 Μm in length and has two right-angle bends. Notably, at the base of ps, the edge is in a zigzag form. 6) In M. gallicum Ax, 2008 , its penis stylet is in ‘C’-shaped, and the distal opening is thickened and bends downwards. The straight-line distance between the base and distal end is approximately 65 Μm.

In contrast, the middle part of penis stylet (ps) of M. heyuanensis n. sp. bends at 108°, while the distal end of penis stylet (ps) bends to a reverse direction. The distal end is apparently swollen and is similar to the corresponding part in M. gallicum . However, the overall structures of their stylets are different, in terms of the straight-line distance between the base and distal end, and the bending angles at the middle and distal end of the penis stylet. In addition, M. heyuanensis n. sp. and M. gallicum live in different habitats (freshwater vs. marine). To sum up, M. heyuanensis n. sp. has significant morphological differences compared with the penis stylets (ps) of the above 6 turbellarians. Together with the results of 18S rDNA analysis, it is evident that M. heyuanensis n. sp. is a new species within the genus Macrostomum .

Figures

FIGURE 1. The locations of three new species of Macrostomum in China

FIGURE 2. Macrostomum heyuanensis Wang & Sun, n. sp.: (A – F) photographed in life; (G and H) penis stylet; (I) sperm.

FIGURE 3. Macrostomum heyuanensis et al., n. sp.: (A) horizontal whole body section; (B – D) longitudinal whole body section.

FIGURE 4. Macrostomum heyuanensis Wang & Sun, n. sp., ventral view: (A) body in whole; (B) profile of the tail; (C) copulatory apparatus; (D) penis stylet; (E) sperm.

FIGURE 5. The phylogenetic tree of 18 s rDNA generated with Maximum Likelihood method. (bootstrap = 1000, Tamura-nei type)

FIGURE 6. The phylogenetic tree of 18 S rDNA gene generated with Neighbor-Joining method. (bootstrap = 1000, Kimura 2 - parameter type)