Gyraulus chinensis (Dunker, 1848)

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 : 6-7

Gyraulus chinensis (Dunker, 1848)

(Basommatophora: Planorbidae )

Figs 4 , 5

Identification

Gyraulus chinensis is readily distinguished from the two indigenous species of Gyraulus in South Africa, G. connollyi Brown & Van Eeden, 1969 and G. costulatus (Krauss, 1848) , by means of the characteristic dark pigmentation on its mid-dorsal mantle, head and tentacles, and its flatter and smoother shell ( Brown et al. 1998; Brown 2001). In addition the shell of G. chinensis grows larger, to 6.5 mm ( Brown et al. 1998), than either of the indigenous species, which rarely reach 5.0 mm ( Brown & Van Eeden 1969). It is typically pale coloured with weak or no spiral sculpture and a rounded shoulder ( Figs 4 and 5 ).

The pigmentation is seen on the head, anterior mantle and tentacles in both live and preserved specimens ( Fig. 4 ). The ‘flatness index’ of a discoid shell was defined by Brown and Van Eeden (1969) and Brown et al. (1998) as the product of the whorl diameter from shoulder to the inside of the aperture and whorl height. The index increases with increasing whorl diameter. For G. chinensis from Amatikulu it ranged from 1.9 in juveniles of 1 mm diameter to 4.0 in adults of 4.5 mm diameter (Fig. 6) whereas in G. connollyi , the closest indigenous species (see key below), the whorls were higher relative to width so that the index was consistently below 3.0 ( Brown & Van Eeden 1969). The two largest specimens of G. chinensis measured 5.65×1.4 and 5.75× 1.35 mm

(Fig. 7). This figure shows that the number of whorls also increases with shell diameter from approximately 2.75 for shells less than 2 mm diameter to a maximum of 4.75 whorls for shells over 5.6 mm diameter.

The reproductive anatomy of the Amatikulu material conformed well to the descriptions of G. chinensis given by Brown et al. (1998) and Pointier (2008). Important here are the number and arrangement of the lobes of the prostate gland (12–17 lobes of uniform length) and the relative lengths of the preputium and penis sheath (preputium slightly shorter than penis sheath but similar in width). This differs from the two indigenous Gyraulus species, G. connollyi ( Brown & Van Eeden 1969) and G. costulatus ( Brown et al. 1998) . These indigenous species are closely related and have a similar reproductive anatomy. They have fewer than 12 prostatic lobes, which are irregular in shape and arrangement. The preputium is usually longer than the penis sheath in both species though the widest part of the preputium is slightly broader than the penis sheath.

Figures

Fig. 4. Gyraulus chinensis from Amatikulu. Live specimens (4A–B, photos: H. Madsen) and specimen preserved in 70% ethanol (4C, photo: N. Miranda). The shell of the specimen in 4B shows patches of erosion. Note the pigmented mantle in both live and preserved specimens.

Fig. 5. Shell of G. chinensis from Amatikulu (photo: N. Miranda). Scale bar = 1 mm.