Myxobolus wondjii, Lekeufack-Folefack & Feudjio-Dongmo & Tene-Fossog & Wondji & Fomena & Yurakhno & Whipps & Alqurashy & Mansour, 2025

Myxobolus wondjii sp. nov.

urn:lsid:zoobank.org:act:

Figs 1‒2; Table 1

Diagnosis

Myxospores 12.0–13.2 ×8.3–9.4 μm in size; ovoid, slightly tapering anteriorly and with a broad, rounded posterior end; polar capsules ovoid and markedly unequal in size: larger capsule 5.4 × 3.2 µm on average, containing a polar tubule coiled in 9 to 11 turns and occupying anterior half of myxospore cavity, while smaller capsule 1.6×1.0 µm on average, with no visible polar tubule and occupying approximately 1/10 of cavity length. Plasmodia large (100–2000 × 60–1400 µm), subspherical, whitish, and located in interbranchial septa of host gills.

Etymology

The specific epithet wondjii is given in honor of Wondji Charles Synclair, Professor at the Liverpool School of Tropical Medicine, United Kingdom.

Type material

Hapantotype

CAMEROON • gills of Labeo batesii Boulenger, 1911 infected with plasmodia (in Eppendorf tubes (50 ml) containing formalin-fixed); Littoral Region, Nkondjock, Makombè River; 4°42′49″− 4°54′36″ N, 10°10′20″− 10°15′41″ E; GenBank no PQ407595; parasitological collection of the Laboratory of Parasitology and Ecology, Faculty of Sciences , University of Yaoundé I, Cameroon No. Myxo /2024/LPE-002 GoogleMaps .

Taxonomic summary

Type locality

Makombè River, Nkondjock, Littoral Region, Cameroon, 4°42′49″− 4°54′36″ N, 10°10′20″− 10°15′41″ E.

Type host

Labeo batesii Boulenger, 1911 ( Cyprinidae ).

Site of infection

Gill, interbranchial septum.

Vegetative stages

Large, whitish, subspherical plasmodia of variable size were observed on the gills of 66 out of 515 examined specimens of L. batesii , corresponding to a prevalence of 12.8% ( Fig. 1a–b). These plasmodia measured 100–2000 µm in length and 60–1400 µm in width. Up to 27 plasmodia were found per parasitized fish, with infections present on both gill arches. Development appeared asynchronous, as indicated by the presence of plasmodia of various sizes ( Fig. 1a). The gill plasmodia index (mean ± SD) was 2.3 ± 0.6(range: 1−8), indicating a light infection. Overall, the intensity of infection was classified as light.

Description

Histological examination

Histological sections of the gills revealed that plasmodia were located in the connective tissue of the interbranchial septum ( Fig. 1c). The plasmodia exhibited peripheral protrusions, likely resulting from modifications of the surrounding host tissues induced by their growth ( Fig. 1d). At higher magnification ( Fig. 1e), the parasitized tissue showed: (1) alteration and lack of adhesion between the tissue layers surrounding the plasmodium; (2) a multi-layered membrane enclosing the plasmodium, including an outer layer of collagen fibers; (3) presence of monocytes at the plasmodium periphery; and (4) immature myxospores in the peripheral zone and mature myxospores in the median zone of the plasmodium.

Mature myxospores Myxospores were ovoid, slightly tapering anteriorly and with a broad, rounded posterior end ( Fig. 2a). In sutural view, myxospores appeared biconvex ( Fig. 2b). The valves were thick and smooth, with no apparent sutural ridge markings, though the suture line was prominent ( Fig. 2b). Two apically oriented polar capsules were ovoid, markedly unequal in size and converging towards the apex of the myxospore ( Fig. 2a, c–d). The large polar capsule was well developed (5.4 ×3.2 µm on average), containing a polar tubule coiled in 9 to 11 turns and occupying the anterior half of the myxospore cavity ( Fig. 2d). The smaller polar capsule was extremely reduced (1.6× 1.0 µm on average), occupying approximately 1/10 of the cavity length, with no visible polar tubule ( Fig. 2a, c–d). The remainder of the cavity was filled with sporoplasm, which contained an iodinophilous vacuole of variable size, shape, and position ( Fig. 2a, d). Mean myxospore dimensions are provided in Table 1.

Remarks

A striking feature of M. wondjii sp. nov. is the extremely reduced second polar capsule. While not unique among species of Myxobolus , this trait is unusual ( Lom & Dyková 2006). Through examination of species synopses ( Eiras et al. 2005, 2014, 2021) and database searches of more recent articles, we identified 20 species of Myxobolus with distinctly unequal polar capsules.

In some species ( Myxobolus buccoroofus Basu & Haldar, 2004 ; M. harikensis Kaur & Singh, 2011 ; M. mrigalhitae Basu & Haldar, 2003 ; Myxobolus patialensis Kaur & Singh, 2011 ), the smaller polar capsule discharges away from the apex of the myxospore. In others, the smaller polar capsule discharges at the apex ( M. andhrae ( Lalitha Kumari, 1969) ; M. bhadrensis Seenappa & Manohar, 1981 ; M. chilkensis (Kalavati, Vankateswara Rao & Vaidahei, 1992) ; M. duodenalis Kaur & Singh, 2011 ; M. goensis Eiras & D’souza, 2004 ; M. indicum Tripathi, 1952 ; M. labeoi Boungou, Kabre Sakiti, Marques & Sawadogo, 2006 ; M. paratoyamai Kato, Kasai, Tomochi, Li & Sato, 2017 ; M. paratypicus Xi, Zhao, Li & Xie, 2019 ; M. nchoutnounensis Nchoutpouen & Fomena, 2011 ; M. koli Lalitha Kumari, 1969 ; M. mahendrae Sarkar, 1986 ; M. mrigalae Chakravarty, 1939 ; M. saranai ( Tripathi, 1952) ; M. undasuturae Sarkar, 1994 ; M. analfinus Basu, Modak & Haldar, 2009 ).

The species described here, M. wondjii sp. nov., appears to have a degenerate polar capsule with no visible polar tubule. This is most similar to M. bhadrensis , M. chilkensis , M. duodenalis , M. indicum , M. labeoi , M. paratoyamai , and M. paratypicus ( Table 1). Several characteristics differentiate each of these from M. wondjii sp. nov.

Myxobolus bhadrensis was found in the muscle of Labeo rohita Hamilton, 1822 in India. Its myxospores are smaller, with a thickening anterior end, measuring on average 9.5 ×7.1 µm, and a larger polar capsule averaging 3.5 ×2.2 µm.

Myxobolus chilkensis , a gall bladder parasite of L. rohita in India, has spherical to pyriform myxospores (7.2–8.0× 5.6–6.6 μm). Their polar capsules are pyriform, with the larger being 3.2–4.8 ×1.8–2.2 μm in size, and the smaller having a narrow neck.

Myxobolus duodenalis , which parasitizes the inner wall of the duodenum of Wallago attu Bloch & Schneider, 1801 in India, forms smaller myxospores (9.0× 3.2 µm on average). Its larger polar capsule occupies more than half of the myxospore cavity, and the smaller one about one-third.

Myxobolus indicum infects various organs of Cirrhinus mrigala Hamilton, 1822 in India. The larger polar capsule of M. wondjii sp. nov is longer (4.8–6.3 µm) than that of M. indicum (2.7–3.6 µm).

Myxobolus labeoi , a parasite of the fins of Labeo coubie Rüppell, 1832 in Burkina-Faso, has longer myxospores (16–17 µm) and larger polar capsules (average 8.37×6.53 µm).

Myxobolus paratoyamai , a gill parasite of Cyprinus carpio Linnaeus, 1758 in Japan, differs by its elongated pyriform myxospore with a slightly bent anterior end.

Myxobolus paratypicus , a gill parasite of Hypophthalmichthys molitrix (Valenciennes, 1844) in China, has larger myxospores (13.8× 9.9 µm on average) and a larger polar capsule (6.2–8.2×4.2–5.6 µm) that extends beyond the midpoint of the myxospore body.

It is also worthwhile to compare this new species of Myxobolus to Thelohanellus sanagaensis Fomena, Marques, Bouix & Njiné, 1994 , described from the gills of an unidentified Labeo species in Cameroon (Fomena et al. 1994). Although the spores overlap in size and general appearance, T. sanagaensis has only one polar capsule.

SSU rDNA sequence data

The primer sets MC5F and MC3R successfully amplified a 1046 bp fragment of SSU rDNA for Myxobolus wondjii sp. nov. Based on the BLASTn search, this sequence did not match any publicly available myxozoan species. The highest nucleotide similarity was 96.1% with M. nkondjockei (accession number: ON158090 View Materials ), which was reported to infect the scales of the same host, Labeo batesii ( Cyprinidae ). Similarity with other myxozoan species was ≤ 92%. Comparisons with species recently sequenced from freshwater fish in Cameroon revealed the following similarities: 81.4% with M. dibombensis ; 82% with M. opsaridiumi ; and 84.5% with M. makombensis .

Phylogenetic analysis

Trees generated by ML and BI methods exhibited similar topologies, with some differences in support values. Two main monophyletic clades, designated A and B, were recognizable in the consensus tree ( Fig. 3). Myxobolus wondjii sp. nov. clustered within clade B, which primarily comprised species of Myxobolus infecting cyprinids from China. The new species is sister to M. nkondjockei (accession number: ON158090 View Materials ), previously reported from the scales of Labeo batesii in Cameroon ( Lekeufack-Folefack et al. 2022). These two species, in turn, form a sister group with Myxobolus sp. (accession number: OP358475 View Materials ), reported from the gills of Labeo rohita in India. The sister-group relationship between M. wondjii and M. nkondjockei is notable, as both infect the same host species in the same geographic region, albeit in different tissues. This cluster of three species, along with two additional myxobolids, forms a sister group to a larger clade composed mostly of species reported from China. Other species of Myxobolus collected from Cameroon are found in clade A ( Fig. 3), including M. dibombensis (accession number: MG737377 View Materials ) and M. makombensis (accession number: MZ701982 View Materials ), which parasitize the fins and gills, respectively, of Labeobarbus batesii . Clade C includes species infecting marine fishes.