Neodiplostomum, Railliet, 1919

Rensburg, Candice Jansen van, van As, Jo G. & King, Pieter H., 2013, New records of digenean parasites of Clarias gariepinus (Pisces: Clariidae) from the Okavango Delta, Botswana, with description of Thaparotrema botswanensis sp. n. (Plathelminthes: Trematoda), African Invertebrates 54 (2), pp. 431-431 : 434-436

Neodiplostomum type 1 metacercaria

Figs 1B , 2F–H ; Table 1

Neodiplostomum type metacercaria: Prudhoe & Hussey 1977: 136–139, fig. 12. Description:

Metacercaria.

Cysts white. Body divided into a relatively large, dorsoventrally flattened forebody, much smaller hindbody with maximum width occurring pre-acetabular ( Fig. 1B ). Oral sucker subterminal, longitudinally oval ( Fig. 2G ). Acetabulum round to transversely oval. Prepharynx absent. Pharynx longitudinally elongate, opens into oesophagus ( Fig. 2G ). Caecal bifurcation pre-acetabular, extending to level of gonads. Caeca only visible in live specimens. Holdfast organ elliptical, longitudinally elongate, situated post-acetabular ( Fig. 2H ). Single reproductive anlagen round to longitudinally elongate, lying posterior to holdfast organ in forebody ( Fig. 1B ).

Material examined: BOTSWANA:36 metacercariae, Okavango Delta, 18 Shakawe mainstream (18°26'05.0''S 21°54'23.0''E); 18 Xaro mainstream (18°25'19.7''S 21°56'19.9''E) .

Site of infection: Cysts distributed throughout musculature ( Fig. 2F ).

Prevalence of infection: 4.7%.

Remarks: Prudhoe and Hussey (1977) described three diplostomid metacercariae from Clarias gariepinus in South Africa. The first Diplostomum type I was found in the eyes and does not conform to the species in the present study. The second was Diplostomum type II found in the mesenteries. The species from the current survey is similar to it in having the body divided into a fore- and hindbody and possessing a pharynx just posterior to the oral sucker. It differs from Diplostomum type II in that the fore and hind bodies are not as well developed, the gonads are a small mass and not horseshoe-shaped, and the pseudosuckers are not prominent.

The third type was identified as a Neodiplostomum type. The species on hand is similar to it in possessing a fore- and hindbody and has a transversely oval acetabulum. It differs, however, in that the gonads are not situated in the hindbody and the holdfast organ is not situated immediately posterior to the end of the forebody. Bisseru (1956) described three Neodiplostomum species from birds of prey from Africa as well as from the Nile crocodile (Bisseru 1957), but these were all adult specimens and could not be compared to the larval forms. According to Niewiadomska (2002), Neodiplostomum type metacercaria cannot be assigned to adult genera with certainty without knowing their complete life cycle; metacercariae are then referred to as types. This metacercaria is thus assigned to Neodiplostomum type 1. This is the first record of a Neodiplostomum metacercaria in the Okavango Delta, and the first documented record from Botswana.

Figures

Fig.1. Light microscope projection drawings of digeneans from Clarias gariepinus in the Okavango Delta: (A) Clinostomoides brieni Dollfus, 1950; (B) Neodiplostomum Railliet, 1919 type 1 metacercaria; (C) Phyllodistomum bavuri Boomker, 1984; (D) Phyllodistomum vanderwaali Prudhoe & Hussey, 1977; (E) Glossidium pedatum Looss, 1899; (F) Thaparotrema botswanensis sp. n. Scale bars: A, C – 1 mm; D – 0.3 mm; B, E – 0.1 mm; F – 0.2 mm.

Fig. 2. Light and scanning electron micrographs of Clinostomoides brieni Dollfus, 1950 (A–E) and Neodiplostomumtype 1 metacercaria (F–H) from Clarias gariepinusin the Okavango Delta:(A)excysted metacercariae; (B) whole mount;(C) spines on body surface; (D) reproductive system; (E) excretory pore; (F) metacercariae encysted in muscle; (G) oral sucker and pharynx; (H) holdfast organ. Scale bars:A, B – 1 mm; C – 2 µm, D, F – 0.1 mm; E – 20 µm; G – 0.05 mm; H – 0.01 mm.