Sphaeroma octonctum Richardson, 1899 Exosphaeroma amplicauda is a species of marine isopod of the family Sphaeromatidae.

Exosphaeroma amplicauda has a chitinous exoskeleton, with overlapping, articulated dorsal plates, common to members of the order isopoda.

[1] This species has been found in Marin, Sonoma, and San Mateo Counties, California.

In addition, his descriptions do not allow for a definitive identification, as five morphologically similar species exist in the same region.

As a result, in 2015 a neotype was designated to stabilize the taxon, as well as to preserve the original species concept.