This is the one that explains the English name for the whole genus, and it is worth looking at closely because the ribbing is unusually well drawn.
The back is corrugated from end to end in fine parallel ridges. The raised ones are pale green to white, the grooves between them are dark blue-black, and lying in those grooves is a row of short black dashes, so the surface reads as ruled paper. Around the outside runs a bright orange band with a white line just inside it, and the mantle edge itself is thrown into shallow waves rather than running straight.
Nothing stands up off that surface. Arminids have no gill plume: the breathing surfaces are folded away underneath, in the groove between the mantle skirt and the foot, running down both flanks. From above the animal is a closed ribbed shield.
At eight centimeters (3.1 in) it is the largest of the seven arminids in this catalogue by a wide margin, and on open sand beside a soft coral it is a substantial and genuinely striking find.
van Hasselt described it in 1824, which makes it among the oldest names in this section. It has been photographed in the Straits of Tiran.
- pale green and dark ridges alternating down the length of the body
- short black dashes lying in the dark grooves between the ridges
- bright orange margin with a white line just inside it
- eight centimeters, by far the largest arminid here
