It has been found in the eastern Pacific Ocean, from Monterey Canyon to Guaymas Basin, at 1,020–1,314 metres (3,346–4,311 ft) deep.

[1][2] The species is very similar to its relative Myzostoma divisor, having a disk-shaped body around 2 millimetres (0.079 in) long bearing five pairs of parapodia two-thirds of the way to the edge of the disk, as well as a smooth anterior-facing proboscis.

It also possesses two elongated caudal appendages around the cloaca, which in M. josefinae are around the size of the body disk.

[1] The specific epithet josefinae honors polychaete enthusiast Josefin Stiller.

Its closest relative is M. divisor, from which it is distinguished by having marginal cirri of alternating unequal lengths.