Endangered snails are bringing progress on a tram project in Basel to a standstill.

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The mollusks, some as small as two millimetres high, happen to occupy an area where cantonal transport officials want to built a 300-metre-long rail link to connect two existing stations.

A total of 12 different species inhabit the corridor, which runs close to the border of the city of Basel and the canton of Basel-Country.

The problem is that the snails, including the girdled (hygromia cinctella), amber (succinella oblonga) and pupilla muscorum varieties, are in danger of disappearing.

Red-listed by the federal department of the environment, they are a protected species, which is causing headaches for transport planners.

The new rail line would pass through a green space that has not been disturbed for decades.

Despite the small size of the project, “we must take into account a variety of interests,” Jane Hahn from the Basel planning department recently told the Basler Zeitung newspaper.

Federal law stipulates the maintenance or replacement of areas protected for the snails.

This means the soil has to be removed “layer by layer so as not to mix everything up,” Michael Zemp, head of the Basel institute for nature and landscape protection, told the newspaper.

Authorities will have to carefully move the snails without unduly disrupting their activities.

The upshot is that construction on the 17-million-franc project, originally set to start in 2014, will now be delayed until 2015 to accommodate the tiny invertebrates.

Happily, the federal government, which agreed to cover 40 percent of the cost, has agreed to extend its funding for the later year.