Arsole
Yes, believe it or not, there is actually a molecule called Arsole... and it's a ring! It is the arsenic equivalent of pyrrole, and although it is rarely found in its pure form, it is occasionally seen as a sidegroup in the form of organic arsolyls. For more information, see the paper with probably the best title of any scientific paper I've ever come across: "Studies on the Chemistry of the Arsoles", G. Markl and H. Hauptmann, J. Organomet. Chem., 248 (1983) 269. Contrary to popular belief, new research (see reference below) shows that arsoles are only moderately aromatic... Incidentally US patent number US 3 412 119 by the Dow Chemical Company is entitled 'Substituted Stannoles, Phospholes, Arsoles, and Stiboles' - I didn't know there was a substitute for an arsole...
Furthermore, the structure where arsole is fused to a benzene ring is called 'benzarsole', and apparently when it's fused to 6 benzenes it would be called 'sexibenzarsole' (although that molecule hasn't been synthesised yet). Another well known poisonous arsenic molecule is the simple hydride, called 'arsine', with formula AsH3.
And on a related theme, I've been told of an Aryl Selenide compound with the superb shorthand of ArSe, which is both toxic and smelly. The paper it comes from in J. Am. Chem. Soc. was published by authors from, of course, the University of Aarhus!
Also, the related molecule phosphole (which just replaces As with P) is quite amusing if you are a French speaker, since it's pronounced the same as 'fausse folle' (literally false woman), which means both a 'crazy woman' and a 'drag-queen' or 'ladyboy'.