“T”-type channels are categorized amongst the calcium channels, but invertebrate ones, like in the pond snail, Lymnaea stagnalis can masquerade as sodium channels, by gene splicing of a unique veil of extracellular turret residues upstream of the selectivity filter in Domain II coded by Exon 12.
Channels, Volume 2, Issue 7
The cover image illustrates the ambiguous and bipolar nature of the orphan NALCN ion channel which has features of both sodium and calcium channels and has baffled investigators. For more information, see Senatore and Spafford (2013) "A uniquely adaptable pore is consistent with NALCN being an ion sensor, Channels. 7(2):60–8.