[2][3] This centipede is one of only a few species in the genus Mecistocephalus or in the family Mecistocephalidae with more than 55 leg pairs.

[6] He based the original description of this species on specimens collected from two localities near the city of Ningbo in Zhejiang province in China.

[2] Type material including two specimens is preserved at the Natural History Museum in London.

[7] More recently, M. smithii has been described in greater detail based on thirteen specimens (nine females and four males) collected in 2019 and 2020 from four different sites in China, including one near the type locality.

[2] A phylogenetic analysis of ten Mecistocephalus species based on molecular data not only places M. smithii in a clade with M. guildingii, which emerges as the closest relative of M. smithii in a phylogenetic tree, but also places the species M. diversisternus in a sister group for this clade.

The sternites on the anterior leg-bearing segments feature a forked furrow with short branches.

Furthermore, the first article of the forcipule in this species also features two teeth, and the first pair of legs are markedly reduced in size.

For example, M. guildingii not only has fewer legs (only 49 pairs) than M. smithii but also is much smaller in size, reaching only about 4 cm in length.

For example, these centipedes are the only two Mecistocephalus species in Asia to include specimens with 59 leg pairs.