Radix rubiginosa (Michelin, 1831)

Appleton, C. C. & Miranda, N. A. F., 2015, Two Asian freshwater snails newly introduced into South Africa and an analysis of alien species reported to date, African Invertebrates 56 (1), pp. 1-1 : 3-4

Radix rubiginosa (Michelin, 1831)

(Basommatophora: Lymnaeidae )

Figs 1 , 2

Identification

The shape and coloration of the shell of R. rubiginosa is variable and in Africa it can be mistaken for the indigenous Lymnaea natalensis 1 Krauss, 1848, itself a variable species (Brown 1994). Nadasan (2011) used discriminant function analysis to show that both juvenile and adult R. rubiginosa (from Amatikulu) had larger, more broadly ovate shells than L. natalensis from a natural habitat in Glenwood, Durban, with a higher body whorl and narrower aperture, often with a nearly straight outer margin. The maximum recorded shell height and width for R. rubiginosa is 34× 20 mm ( Brandt 1974) whereas for L. natalensis it is 25× 14.5 mm (Brown 1994). The shell of R. rubiginosa is also thicker than that of L. natalensis . Thickness measurements made by Nadasan (2011) 2–4 mm from the outer apertural margins of R. rubiginosa and L. natalensis (n=15 each) were 0.19– 0.16 mm and 0.13– 0.09 mm respectively. Thus the shell of R. rubiginosa grows nearly 10 mm higher and 5 mm broader than L. natalensis and is 0.05–0.07 mm (28.9– 44.2%) thicker.

1 The taxonomy of Lymnaea s.l. is poorly resolved. The species natalensis has traditionally been referred to Lymnaea and we follow this usage, but note that others have referred it to Radix ( Correa et al. 2010) .

The anatomy of lymnaeids is remarkably homogeneous across the family and Nadasan (2011) failed to find any differences between the reproductive systems of R. rubiginosa and the indigenous L. natalensis . The reproductive system of South African L. natalensis was described by Pretorius and Van Eeden (1969).

Molecular analysis

Molecular analyses indicate that the lymnaeids from Amatikulu (RRA) conform to Radix rubiginosa ( Fig. 3 ). The lymnaeid collected in Durban (LND) is the indigenous Lymnaea natalensis as supported by morphological characteristics according to Pretorius and Van Eeden (1969), Brown (1994) (see also the key to Lymnaeidae in South Africa below) and a phylogenetic study on the basis of the 18S rDNA gene ( Nadasan 2011).

Parasitology

Radix rubiginosa is of medical and veterinary importance in its native southeast Asia where it serves as the intermediate host for a variety of trematodes. These include the fasciolid Fasciola gigantica Cobbold, 1855 , the giant liver fluke of domestic stock; three schistosomes (blood flukes), Schistosoma incognitum Chandler, 1926 , Orientobilharzia harinasutai Kruatrachue, Bhaibulaya & Harinasuta, 1965 and Trichobilharzia macgraithi Kruatrachue, 1968 , parasites of various mammals and birds; and two echinostomes Echinostoma malayanum Leiper, 1911 and Hypoderaeum conoideum (Bloch, 1782) ( Brandt 1974; Chitramvong et al. 1981; Bunnag et al. 1983; Woodruff & Upatham 1993; World Health Organization 2005). Fasciola gigantica is a parasite of ungulates, including domestic stock, but may also infect people as do E. malayanum and H. conoideum . The normal hosts of these echinostomes are ducks and rats respectively. None of the schistosomes is able to produce patent infections in exposed people, but their cercariae cause a sometimes severe dermatitis. Radix rubiginosa has also been shown experimentally to be susceptible to the nematode Angiostrongylus malaysiensis Bhaibulaya & Cross, 1971 which may also infect people ( Dondero & Lim 1976). The discovery of R. rubiginosa in South Africa is therefore of veterinary importance since F. gigantica infection is a recognised problem in domestic stock in the country ( Reinecke 1983). The only known snail host for F. gigantica in South Africa is Lymnaea natalensis , which occurs widely in both flowing and standing water bodies across the northern, eastern and southern parts of South Africa ( De Kock et al. 2001). If R. rubiginosa is susceptible to the South African strain of F. gigantica , it could exacerbate the transmission of fascioliasis in the lowlands of KwaZulu-Natal and possibly further north as well.

Figures

Fig 3. (A) Tree based on 533 nucleotides of the cytochrome c oxidase subunit ImtDNA of lymnaeid samples, with the outgroup Planorbis corneus. (B) Tree based on 360 nucleotides of the mt 16S rDNA of lymnaeid samples, with the outgroup Stagnicola elodes. Numbers on branches represent Bayesian posterior probabilities percentages, neighbour-joining and maximum parsimony bootstrap values, respectively. Only values greater than 50% are shown; * indicates support of <50% for distance analysis. Figures adapted from Nadasan (2011). RRA – lymnaeid samples from Amatikulu, South Africa; LND – lymnaeid samples from Durban, South Africa.

Fig. 1. Radix rubiginosa from Amatikulu (photos: H. Madsen).

Fig. 2. Shells of Radix rubiginosa from Amatikulu (photos: N. Miranda). Scale bars = 5 mm.