A. fascicularis, Croatia (left) and A. crinita (right). Intermediate valves and girdle. Anterior at top of both images.
Intermediate valves (1) on:
A. fascicularis are narrower than, or about same width as, girdle to one side of them (2).
A. crinita are distinctly wider than the girdle to one side of them (2).

Girdle extensions (3) running between valves from each side on:
A. fascicularis meet, or almost meet with a gap (4) of about 5% of the chiton’s width.
A. crinita do not meet; they are separated by a gap (4) about 20% of the chiton’s width.
The above applies to extended specimens adhering to the substrate. Both expose more girdle when curled up.

KEY ID FEATURES and similar species at: 01 Acanthochitona crinita