Fig. 1

The geographical distribution of B. straminea in Hong Kong. The grey circles denote sites where B. straminea was absent; ZD and LD (marked in grey) represent sites containing snails with morphological resemblance to B. straminea, which were not B. straminea as suggested by the molecular data (i.e. false positive sites). The blue circles represent the B. straminea-positive sites whereas only black shell snails were found. The red dots represent B. straminea-positive sites with coexistence of red- and black- shelled snails. The green pentacle represents a site with only dead snails and shells found (proven to be B. straminea by molecular data). The blue triangles represent sites containing B. straminea reported in the 1980s [18]. Note that the site PCL contains B. straminea in both the present and previous studies