"Navanax " is not a nudibranch, even though it somewhat resembles one; it belongs to a more ancient lineage of opisthobranchs called the cephalaspideans or head shield slugs and snails.
42.
"C . kunmingensis " looked like a crustacean, with a broad, almost heart-shaped head shield, and a long body with many pairs of legs of varying sizes.
43.
"S . coalescens " is unique among arthrodires in that the head shield and the trunk shield are fused or " firmly sutured " together in an immobile, helmet-like unit.
44.
A two-piece, all-metal armour plate head shield was added, as on the E-4, to the hinged portion of the canopy, although some lacked the curved top section.
45.
The defining characteristic of all galeaspids was a large opening on the dorsal surface of the head shield, which was connected to the pharynx and gill chamber, and a scalloped pattern of the sensory-lines.
46.
The larvae are dark brown with yellow to orange spots symmetrically located in the lateral region of the segmented body, in each case at the head shield, and on the third, fourth, eighth and tenth segment.
47.
All species possessed a long spathe-like rostrum derived from the anterior-most end of the head shield, which would have enhanced the fish's hydrodynamics and was probably also used to root out food buried beneath the substrate.
48.
As opposed to most vipers, where the head is distinct from the neck and covered with small scales, in " Causus " the head is only slightly distinct from the neck and covered with 9 large, symmetrical head shields.
49.
It retains some of these serrations throughout its life . " The head shield extends down the side of the head to just above the tympanum, and the top of the neck has prominent pointed tubercules ( many of these with an apical sensory pit ) ."
50.
A distinguishing feature is a white mark shaped like the letter w across the anterior edge of the head, although this may only be partially visible on some specimens, and a white or pale yellow crescent-shaped spot at the posterior edge of the head shield.
