Extended length 36 mm. Split, Croatia. July 2012. © J. Prkić.
In dorsal view, the shape of an A. fascicularis specimen can vary. Here it is at maximum extension with the width reduced to about 46% of its length.

The exposed parts (tegmentum) of the valves of this one (seen through the translucent, coloured properiostracum) are a typical assortment of mottled and streaked white, yellow, brown and black.
The girdle of this one is ochre, best seen between the valves and at the bases of the sutural tufts as the covering properiostracum has much dark pigment and dark spicules.
The perinotum (dorsal surface of the girdle) has, adjacent to the anterior edge of each intermediate valve (ii to viii), a sutural tuft of numerous, thin, 13µ to 24µ (Schmidt-Petersen et al., 2015), needle-like, translucent spicules up to about 2mm long. They may be colourless, but are often tinted; in this case jade green. The tail valve (viii) has two tufts at its posterior and the head valve (i) has four tufts at its anterior, making a total of eighteen tufts.

KEY ID FEATURES : 01 Acanthochitona fascicularis