Freshwater samples were collected during routine sampling from January 2014 to April 2015 at four sampling sites located along a 25-km stretch of the Mooi River system near Potchefstroom in the North West province, South Africa (Figure 1). At each site, a 100-ml grab sample was taken, and the unpreserved samples were left overnight to be examined the next day.

Sub-samples were transferred to an Utermohl sedimentation chamber. Algae were identified to species level with an inverted Zeiss light microscope. Literature consulted for identification of A. vegetans includes Belcher and Swale (1972), Starmach (1985), Lee and Kugrens (1989) and Baker (2012). Measurements of cell and colony sizes were made by means of a ruler in one of the eyepieces of the microscope.

Anthophysa vegetans (O.F. Müller) Stein in Der Organismus der Infusionthiere nach eigenen Forschungen in Systematischer Reihenfolge bearbeitet. I Hälfte: 36, legend to pl. V [5]: 1, 1’ (1878). Basionym: Volvox vegetans O.F. Müller in Animalcula infusoria fluviatilia et marina quæ detexit: 22, pl. III [3]: figs 22–25 (1786). Synonym: Anthophysa muelleri Bory, nom. illeg. superfl., in Dictionnaire Classique d’Histoire Naturelle. 1: 427, 597 (1822).

Type: DENMARK, in freshwaters, November 1779 and 1780, illustration in Müller in Animalcula infusoria fluviatilia et marina quæ detexit: 22, pl. III [3], figs 22–25 (1786).

Attachment of Anthophysa colonies is by means of an inorganic stalk (Figure 2) that becomes encrusted with deposits of calcium phosphate and precipitates of iron and manganese (Baker 2012; Misner 2009). In Pringsheim (1946), the morphology and development of the stalk is described and specific reference is made to its dependence upon soluble iron and manganese compounds. The mineralised stalk is often branched (Guiry & Guiry 2016) and is the species’ most valuable diagnostic feature (Figure 2). Stalks vary greatly in diameter, increasing towards the base (Belcher & Swale 1972) and are brownish in colour, though the colour is dependent on the age and the mineral composition of the stalk. Lee and Kugrens (1989) found that the addition of FeCl₃ resulted in yellow stalks, while the addition of MnCl₂ resulted in dark orange-brown stalks. Bacteria are usually visible on the stalks. Belcher and Swale (1972) speculated that the origin of the stalks was mucilage secretions of the Anthophysa cells.

Spherical or hemispherical colonies (Belcher & Swale 1972) can be found on top of the stalks and these, as well as individual cells, are capable of separating themselves from the stalks and becoming fixed to commence new colony formation. Colonies can swim freely, with a rolling motion similar to that performed by Volvox (Clark 1866). The number of individuals forming a colony ranges from 2 to 50 (Clark 1866).

The small (7–10 x 5–7 µm), colourless cells within the colonies are obpyriform or obconical (Belcher & Swale 1972), that is, wide at the anterior end, narrowing towards the posterior end (Figure 2). Food is taken in at one side of the anterior end in a gullet-like furrow. Each cell has two unequal flagella situated next to the furrow where food is taken in. The long flagellum is slightly curved (Figure 2) and usually body length (but not longer than 30 µm) and contains two rows of tripartite hairs. The second, short and delicate flagellum, usually half of the body length (maximum length of 5 µm), has a smooth surface (Belcher & Swale 1972). The short flagellum is situated at a right angle to the long flagellum. The long flagellum can be used to propel the cell forward. Food is obtained by phagotrophy or through the oxidation of organic substances (chemo-organotrophy, Belcher & Swale 1972).

According to Belcher and Swale (1972) A. vegetans is widely distributed, and literature searches revealed its presence in the freshwaters of most continents, including Europe, Asia, North and South America, and Australia (Figure 1). In Africa, it has been recorded only once before, in the Jakara Dam in Nigeria by Abubakar and Abdullahi (2015). No records could be found of this species’ presence south of Nigeria on the African continent. Anthophysa is commonly found in freshwater systems that contain high concentrations of iron and manganese that precipitate in the stalks (Pringsheim 1952; Starmach 1985). The Mooi River in North West province, South Africa, where the species was collected, receives contamination from a wide variety of point and diffuse sources. The Wonderfonteinspruit, a tributary of the Mooi River, flows through the richest gold mining region in the world and has been exposed to pollution for more than a century (Hamman & Van Rensburg 2012). Large-scale mining, together with storm water, and effluent from several urban and industrial areas, as well as informal settlements, contaminate the water (Van der Walt et al. 2002). Contaminants include heavy metals such as iron and manganese (Hamman & Van Rensburg 2012). Increased levels of heavy metals were also reported from the sediments of the Mooi River (Wade et al. 2000).

SOUTH AFRICA. North West province: Mooi River near Potchefstroom, 26°30’12.25”S, 27° 7’31.81”E, 14 January 2014, De Wet 1 (PUC), (Figure 2).