A Ballchinian is a race of "unique" dominics. They have human appearances, and long sagging faces. But, they have one feature different from humans. They (males at least) have genitalia on their chin (which explains their name). This is their weak spot, as they are fairly strong against other hits, which may be why they wear large ballsacks.
In Men in Black II, Serleena enlists a series of aliens to stop Kay and Jay. Kay kicks one alien's crotch to no avail, when Jay reminds him he is a Ballchinian. Kay exposes his "balls" and kicks him there. No other Ballchinians are shown.