Parasites of South African freshwater fish. 4. Description of Spirocamallanus daleneae n. sp. (Nematoda: Camallanidae) from Synodontis zambezensis Peters, 1852 (Mochokidae) with comments on Spirocomallanus spiralis (Baylis, 1923). Onderstepoort Journal of Veterinary Research, 60(2), June 1993: 131-137. 132 [Zoological Record Volume 131]