You can define any shape to be included in the list of available arrow styles. Only the form of the shape is added as a black filled arrowhead.
Use the draw functions to create the shape to be used as an arrow style.
Select the shape and choose.
In the dialog, click thetab.
Click \<emph\>Add\</emph\> and assign a name to the new arrow style.
Click \<emph\>OK\</emph\> to close the dialog.