Porous roundworm (Labronema porosum) and Mount Bidoup roundworm (Labronema bidoupense) from Vietnam

NEWS - Researchers have established porous roundworm (Labronema porosum) and Mount Bidoup roundworm (Labronema bidoupense) from natural habitat in Vietnam as new species based on morphological and molecular characters (18S rDNA and 28 rDNA). The two new taxa belong to the group of L. ferox Thorne 1939 with a length of 1.5-2.5 mm, odontostyle 31-39 μm and a lip region offset by a constriction.

Labronema Thorne 1939 is a large and diverse dorylaimid genus with complex taxonomy. The study also shows that the population from Vietnam previously identified as L. glandosum Rahman, Jairajpuri, Ahmad & Ahmad 1986 actually represents L. porosum.

L. porosum gets its nickname reflecting its prominent ventral and lateral body pores. This species is 1.6-2.25 mm long, odontostylic (32-37 μm), weakly angled and offset by a narrowed lip area, 21-24 μm wide, there is a cuticular fold on the dorsal side of the stoma, the uterus is not differentiated, the vulva is longitudinal (V = 48.5-59%). the tail is short and rounded (25-30 μm, c = 53-90, c’ = 0.5-0.6).

This new species resembles L. andrassyi Gagarin 1992, L. brevicauda Furstenberg Heyns & Swart 1993, L. gerlachi Andrássy 2011, L. glandosum and L. obesum Thorne 1974, but can be distinguished from all of them by the distinctive cuticular fold on the dorsal side of the stoma.

L. bidoupense is nicknamed after Mount Bidoup. This species is characterized by a length of 1.59-2.04 mm, a lip area balanced by a deep constriction with a width of 25-28 μm, odontostyle length 37.5-39 μm, uterus complex (tripartite), longitudinal vulva (V = 54-57%), short and rounded tail (26-31 μm, c = 57.8-77.2, c’ = 0.5-0.6).

Males with spicules 68-83 μm long, 5-6 times longer than the ventromedian supplements which are wide and connected in number 13-15, leaf-shaped lateral cuts. This species resembles L. andrassyi, L. brevicauda, L. gerlachi, L. glandosum, L. obesum and L. porosum.

An integrative taxonomic approach for L. porosum and L. bidoupense contributes to the knowledge of the large and complex genus Labronema. Both species are morphologically and genetically very close to form a well-supported clade with the type species and L. vulvapapillatum or Vakil Kandi population (Iran).

Other populations identified as L. vulvapapillatum from the Netherlands and Kerman Province (Iran) clustered together in the 18S rDNA tree and were closely related to the clade. Clearly, L. vulvapapillatum populations from the Netherlands and Kerman Province are not conspecific with the Vakil Kandi population.

28S rDNA sequencing of two Labronema populations from Du Gia Nature Reserve (Bac Me District, Ha Giang Province) and Cuc Phuong National Park (Ninh Binh Province) confirmed that the population previously recorded as L. glandosum from Cuc Phuong National Park is identical to L. porosum.

It is very difficult to assess the phylogenetic relationships of Labronema with other genera using an integrative approach due to the very low number of species studied, also affecting the reconstruction of the evolutionary history of dorylaimid groups at higher taxonomic levels.

Original research

Vu TTT, Elshishka M, Nguyen AD, Le TML, Mladenov A, Peneva V (2024). Two new species of genus Labronema Thorne, 1939 (Nematoda, Dorylaimidae) from natural parks of Vietnam with an identification key to the species with a medium-sized odontostyle. ZooKeys 1215: 1-26, DOI:10.3897/zookeys.1215.128183

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