Tag Archives: Gastrodontidae

The “orange spot” (Zonitoides nitidus) revisted

Black Gloss, Orange Spot

In in earlier post, I mentioned how the black-bodied Zonitoides nitidus (common name: Black Gloss) has an orange-coloured spot that is visible through the translucent shell (although apparently not always that orange but more yellowish). In the photograph I included at the time, this spot was just barely visible if one knows where to look. Here I add another photograph, showing this character much more clearly (and with a giant arrow to point it out).

Zonitoides nitidus. Lundar Beach Provincial Park (E shore of Lake Manitoba), Manitoba.

Zonitoides nitidus

Black Gloss, orange spot

Zonitoides nitidus

Zonitoides nitidus, photographed at Thompson Regional Park, Chilliwack River valley, in May 2013.

Two species of Zonitoides, Zonitoides nitidus (Müller, 1774) and Z. arboreus (Say, 1817) occur in Canada (and BC). Sometimes, material in collections are confused because shells are often difficult to identify with certainty. Zonitoides nitidus grows to a slightly larger size, has a somewhat higher spire, and lacks the exceedingly fine and very weak spiral striae of Zonitoides arboreus. However, a better way to distinguish species is by the body pigmentation. Zonitoides nitidus (as its name suggests) has an entirely blackish body; that of Z. arboreus is lighter along the sides of the foot. There is also a spot, not present in the other species, that is sometimes described as “dull orange” and can be seen through the shell a little ways back from the aperture, especially in retracted animals. Take a look a the snail in the upper left of this photograph and you might make out this orangish spot.