Diplostomum sp.

Hoogendoorn, Coret, Smit, Nico J. & Kudlai, Olena, 2020, Resolution of the identity of three species of Diplostomum (Digenea: Diplostomidae) parasitising freshwater fishes in South Africa, combining molecular and morphological evidence, International Journal for Parasitology: Parasites and Wildlife 11, pp. 50-61 : 58-59

publication ID	https://doi.org/ 10.1016/j.ijppaw.2019.12.003
persistent identifier	https://treatment.plazi.org/id/03EA8781-FF8D-5130-E27A-B0992DA457E7
treatment provided by	Felipe
scientific name	Diplostomum sp.
status

Treatment

3.3.3. Diplostomum sp. 16 sensu Locke et al. (2015)

Description ( Fig. 4g− i View Fig )

[Based on 15 ethanol-fixed metacercariae. Measurements are provided in Table 5]. Body elongate-oval, with maximum width at level of ventral sucker or just anterior to ventral sucker. Tegument covered with numerous tiny spines. Forebody elongate-oval, longer than hindbody. Hindbody rounded, short. Forebody/hindbody length ratio 1:0.19–1:0.27 (1:0.23), forebody/hindbody width ratio 1:0.31–1:0.49 (1:0.41). Pseudosuckers elongate-oval, everted (n = 14; Fig. 4g View Fig ) or inverted (n = 1; Fig. 4h View Fig ). Oral sucker subterminal, elongate-oval. Prepharynx short; pharynx muscular, elongate-oval; oesophagus short; caeca long, reach posterior to holdfast organ. Ventral sucker transversely oval, equatorial, equal or larger than oral sucker [oral/ventral sucker width ratio 1:0.95–1:1.50 (1:1.25)]. Distance from ventral sucker to anterior end of body, 128–207 (167) and to posterior end of forebody, 105–158 (133). Holdfast organ transversely oval, in posterior part of forebody, contiguous with ventral sucker. Excretory granules, medium-sized, grouped into two lateral extracaecal and one median field. Excretory vesicle V-shaped; reserve excretory system of diplostomid type. Excretory pore subterminal, oriented ventrally.

Second intermediate host: Southern mouthbrooder Pseudocrenilabrus philander (Weber, 1897) ( Perciformes : Cichlidae ).

Localities: River Mooi (26̊33′58″S, 27̊07′16″E).

Prevalence: 9 of 10.

Intensity of infection: 3–21 metacercariae per fish.

Voucher material: 15 voucher specimens deposited in NMB P 531–533 View Materials [ NMB P 531 View Materials (7 specimens), NMB P 532 View Materials (5 specimens), NMB P 533 View Materials (3 specimens), all from P. philander , River Mooi , North West Province, South Africa] .

Representative DNA sequences: 28S – 2 sequences (MN813532; MN813533), ITS1-5.8S-ITS2 – 5 sequences (MN813545 – MN813549), cox 1 – 5 sequences (MN808625 – MN808629).

3.4. Remarks

The three species of Diplostomum described above represent species that were previously reported from freshwater fishes in Nigeria ( Chibwana et al., 2013), Iraq and China ( Locke et al., 2015) based on the analyses of molecular data. The previous reports did not include morphological descriptions of the metacercarial isolates and, thus our study provides the first morphological characterisation of these three species of Diplostomum linked to molecular sequences. Morphologically, metacercariae of the present species are well-distinguishable from each other. The most characteristic feature differentiating metacercariae of Diplostomum sp. from the two other species in our study is the presence of pseudosuckers of the sunken type. In addition the metacercariae of Diplostomum sp. differs from both, Diplostomum sp. 14 and Diplostomum sp. 16 by the shape (subsperical body vs elongate-oval vs elongate-oval, respectively) and size of body [379–615 × 456–525 (497 × 491) vs 237–372 × 206–271 (302 × 240) vs 284–434 × 212–306 (356 × 254)], longer prepharynx [42–92 (60) vs 3–7 (5) vs 8–22 (15)], larger pharynx [42–65 × 31–41 (50 × 35) vs 28–38 × 15–27 (33 × 22) vs 31–39 × 20–28 (36 × 24)], ventral sucker [66–87 × 100–112 (75 × 106) vs 31–49 × 34–53 (40 × 44) vs 40–55 × 52–68 (49 × 61)], oral/ventral suckers ratio [1:1.98–1:2.29 (1:2.12) vs 1:0.84–1:1.28 (1:1.05) vs 1:0.95–1:1.50 (1:1.25)] and holdfast organ [104–123 × 141–196 (115 × 165) vs 52–87 × 58–91 (68 × 73) vs 77–99 × 84–124 (91 × 101)]. Furthermore, the size and distribution of the excretory granules in the metacercariae of Diplostomum sp. , i.e. medium-sized and scattered throughout the forebody, differs from the state observed in the two other species where the excretory granules are of small to large size and grouped into two lateral extracaecal and one median field.

Although the body length and width of the metacercariae of Diplostomum sp. 14 and Diplostomum sp. 16 overlap in range [237–372 × 206–271 (302 × 240) vs 284–434 × 212–306 (356 × 254)], the measurements of the metacercariae of Diplostomum sp. 14 is on average smaller than those of Diplostomum sp. 16. Diplostomum sp. 14 further differ from Diplostomum sp. 16 in having a smaller oral sucker [36–55 × 35–53 (45 × 43) vs 51–62 × 38–59 (55 × 49)], shorter prepharynx [3–7 (5) vs 8–22 (15)], smaller ventral sucker [31–49 × 34–53 (40 × 44) vs 40–55 × 52–68 (49 × 61)] and smaller holdfast organ [52–87 × 58–91 (68 × 73) vs 77–99 × 84–124 (91 × 101)].

Morphologically, the metacercariae of Diplostomum sp. strongly resemble the metacercariae of Diplostomum longicollis Zhokhov (2014) reported by Zhokhov (2014) from Enteromius humilis (Boulenger, 1902) and Garra dembecha Getahun and Stiassny, 2007 in Ethiopia in the presence of pseudosuckers of the sunken type. However, morphometric data comparisons of the fixed metacercariae revealed that the specimens in our study exhibit shorter body [379–615 (497) vs 612–1,008 (748)], smaller oral sucker [36–55 × 48–54 (48 × 50) vs 66–72 × 66–72 (63 × 65)], shorter prepharynx (42–92 vs 72–180), lower low limits for pharynx length (42–65 vs 60–66) and ventral sucker length (66–87 vs 72–96), and smaller holdfast organ [104–123 × 141–196 (115 × 165) vs 132–180 × 150–252 (158 × 183)].

The metacercariae of Diplostomum sp. 14 are morphologically most similar to the metacercariae of D. montanum Zhokhov (2014) from the eye lenses of E. humilis , G. dembecha , L. gorgorensis , V. beso and D. tilapiae Zhokhov (2014) from the eye lenses of O. niloticus collected in Ethiopia ( Zhokhov, 2014). These similarities include: the shape of the body and pseudosuckers, position and size of the holdfast organ in relation to the ventral sucker and position of the ventral sucker. However, almost all body dimensions of metacercariae in our material are smaller than those of metacercariae of D. montanum and D. tilapiae as described by Zhokhov (2014) (see Table 5 for details).

The metacercariae of Diplostomum sp. 16 possess features similar to metacercariae of Diplostomum garrae Zhokhov (2014) found in the eye lens of G. dembecha in Ethiopia ( Zhokhov, 2014). These include shape of the body, pseudosuckers and holdfast organ and the position of the ventral sucker. Metacercariae of Diplostomum sp. 16 can further be distinguished from D. garrae in having a lower low limits for a number of features, including length and width of body, oral sucker, pharynx, ventral sucker, holdfast organ and the length of the prepharynx (see Table 5 for details).

It should be noted that metacercariae reported in the present study were not compared to the four species of Diplostomum , D. heterobranchi Wedl, 1861 , D. magnicaudum El-Naffar (1979) , Diplostomum sp. type I Prudhoe and Hussey (1977) and Diplostomum sp. type II Prudhoe and Hussey (1977) collected in the brain or encysted in the mesenteries of the North African catfish Clarias gariepinus (Burchell, 1822) in Egypt and South Africa ( Prudhoe and Hussey, 1977; Khalil and Polling, 1997), because detailed examination of the descriptions and illustrations of the metacercariae of these species suggested that their placement within the genus Diplostomum was erroneous.