  Analogous to the types A, B, and C cases, we address the computation of the
index of seaweed subalgebras in the type-D case. Formulas for the algebra's
index can be computed by counting the connected components of its associated
meander. We focus on a set of distinguished vertices of the meander, called the
tail of the meander, and using the tail, we provide comprehensive combinatorial
formulas for the index of a seaweed in all the classical types. Using these
formulas, we provide all general closed-form index formulas where the index is
given by a polynomial greatest common divisor formula in the sizes of the parts
that define the seaweed.
