No etymology given, suggested by Christopher Scharpt: from Latin 'eu' for 'true' and 'iota' for anything very small, in combination 'truly very small' referring to it as being the smallest vertebrate at the time it has benn described by Jenkins (thus, making the suggestion by Scharpt plausible.
Etymology of specific name :
Name from Latin 'atrus' for black and 'venter' for belly, referring to the black pigment in the area of the abdomen; an adjective.