The record of Asian endemic Netzelia tuberspinifera in Vietnam

The testate amoeba species Netzelia tuberspinifera (Hu, Shen and Gong, 1997) Gomaa et al., 2017 was firstly discovered and described as Difflugia tuberspinifera in 1997 in the Wujiang River (Guizhou province, China). Then, Yang et al. (2004) redescribed in relatively detail the morphological characteristics of this species based on two populations at Xinzhou and Mulan lakes (Hubei province, China). The above descriptions all indicate that individuals of this species have 4-8 sharp spines on their shells. However, at the Xiamen reservoir (Fujian province, China), Yu et al. (2014) observed an additional morphotype of D. tuberspinifera, in which the individuals did not have spines on the shell. Results of statistical analysis of the above study showed that there was no difference in morphological parameters (length, width, aperture diameter, neck height and number of teeth on the aperture rim) between the spiny and spinless groups of individuals. Until 2015, this species has only been observed in China and is considered as asian endemic.

During the implementation of the project "Initially study on species diversity and distribution of Testate amoebae in some southern provinces of Vietnam" (2015-2016), the research group of Vietnamese-Russian Tropical Center has found Netzelia tuberspinifera in the Ta Mon Lake (Binh Thuan province) and Buu Long Lake (Dong Nai province) (Tran and Mazei, 2018).

Then, when carrying out the project "Study on species composition and distribution of Testate amoebae in water bodies in national parks Ba Vi, Tam Dao, Ba Be, Cuc Phuong and surrounding areas" (2017-2019), the research group continued to record the species Netzelia tuberspinifera in Suoi Hai lake (Ba Vi, Hanoi), Yen Quang lake, Mac lake (Ninh Binh province), Ba Be lake (Bac Kan) and Thanh Lanh lake (Vinh Phuc) (Tran et al., 2021). Both spiny and spineless phenotypes were observed.

Suoi Hai Lake (Ba Vi, Hanoi)

N. tuberspinifera has a spherical shell, the surface of which have relatively uniform circular protrusions that are located close together. The shell is made of small granular or plate sand. The aperture is symmetrical, with relatively equal teeth, the number of which is usually 8-10. In the lateral view, aperture has a short collar. Spinless or spiny shells, the number of which can range from 1-5 (for populations in Vietnam), spines are located in the middle part of the shell. The spine length on each shell can be uniform or very variable. The morphological parameters based on the populations at Suoi Hai and Yen Quang lakes: shell length 77-123 µm, shell width 73-124 µm, aperture diameter 32-64 µm, collar height 6-20 µm, spine length 10-54 µm, number of spines 0-5. Aperture diameter is about ½ of shell length and width.

Image of the species Netzelia tuberspinifera observed under an optical microscope. a-d: lateral view; e: aperture view; f-i: different number of spines on the shell; j: protoplasm; k: cell division. Scale bar: 20 µm (Source: Tran et al., 2021).

Based on data of the morphological parameters of the species, it can initially be seen that the shell length and width of the populations of N. tuberspinifera in Vietnam is smaller than that of the populations in China, the number of spines on shells are also less, with only up to 5 spines recorded, while individuals of N. tuberspinifera in China can have up to 8 spines on the shell. Some Chinese scientists have shown that N. tuberspinifera is a predator that feeds mainly on several species of rotifers and copepods. However, we also found that in the protoplasm of N. tuberspinifera cells there are symbiotic algal cells, which can serve as another source of nutrients for N. tuberspinifera. The species composition of symbiotic algae and their role in N. tuberspinifera need to be clarified in further studies.

Image of symbiotic algal cells in the protoplasm of Netzelia tuberspinifera (arrow pointing). Scale bar: 20 µm. (Photo: Hoan Tran).

It is worth noting that at the sampling time of September 2017, N. tuberspinifera was recorded at Suoi Hai Lake with high density, however, during the monthly monitoring (from June 2020 to April 2021) at 7 different stations on Suoi Hai Lake, this species is no longer observed. The next question that needs to be answered is whether this species really "disappears" from Suoi Hai Lake and if so, what is the reason here?

Source:

Tran H.Q., Mazey Yu.A. (2018). Seed amoebae from water bodies of South Vietnam with a description of a new species Difflugia vietnamica sp. Nov Acta Protozoologica. 57: 215-230.

Tran H.Q., Tran V.T. Kh., Tikhonenkov D.V. (2021). Freshwater shell amoebae from water bodies of North Vietnam with the detection of indicator species. Limnology. 22: 151-160.

Article and photos: Dr. Tran Quoc Hoan / Institute of Tropical Ecology