Arion subfuscus group? (sp. in this genus can only be IDd by inspection of genitalia; should have yellow to orange mucus, this one shows a mucus plug of that color

2013-5-9 Newark Oaks, DE
the mucus plug is foul tasting and, in some slugs, anesthetizing and is a defense against predators

Dusky Arion
http://www.carnegiemnh.org/science/mollusks/va_arion_subfuscus.html

Dusky Slug
http://idtools.org/id/mollusc/factsheet.php?name=Arion%20subfuscus%20group:
%20Arion%20subfuscus