User:Hemiauchenia/sandboxWaptia

Known specimens of Waptia range in length from 13.5 to 66.5 mm with the vast majority ranging (~85%) being 40 to 60 mm long. The bivalved carapace was saddle shaped, and was thin and non mineralised, and was likely flexible in life. The carapace was laterally compressed, substantially longer than it was wide, and had no distinct boundary between the two halves. The carapace was only attached to the body in a small section near the front of the head.

The front of the head bore a pair of reniform (kidney shaped) eyes, about 1 mm across, which are born on short stalks. One specimen with preserved ommatidia shows that density of ommatidia in the eye was about 600 per square millimetre. It is suggested that this allowed a significant amount of side and front-orientated vision. A pair of small lobes, about 1 mm long, protrude near the eyes. Similar structures are known from the related Canadaspis as well as other mandibulates, and are thought to correspond to the hemi-ellipsoid bodies of crustaceans, and thus likely have an olfactory function. Between the eyes is a triangular structure, dubbed the "median triangular projection", which is probably homologous to the ‘anterior sclerite’ of other Cambrian arthropods. The head bears a pair of antennae, which are composed of 10 elongate cylindrical segments/podomeres, which sequentially reduce in width towards the tip of the antenna. The front ends of each podomere bear setae, which are orientated at an angle of 75° to 95° relative to the antennae axis.

The mandibles have a three-segmented projection, which are covered with setae. The strucure shows evidence of sclerotisation toward the edge where the two mandibles contacted, which have a toothed margin. The mandibles likely had a biting and grinding function. The maxillules are composed of at least six, probably nine podomeres, the end podomere bears a pair of claws, along with numerous setae. These likely assisted food manipulation alongside the mandibles. The cephalothorax has four additional pairs of uniramous leg-like appendages, the first three of which are well segmented, with 5 endopod segments, with a terminal claw with a 4 or 5 segmented basipod with well developed endites, particuarly on the first pair, which project inward from the legs. The fourth leg differs in the fact that only the very end of the leg is segmented, with the rest being annulated, with the annulated regions being fringed by lamellae.

The "post-cephalothorax" has 5 segments, associated with 6 pairs of uniramous appendages (and 6 corresponding somites), which are fringed with lamellae. The following abdomen is approximately 60% of the total length, with 6 segments and no corresponding legs, which teminates in forked tail fluke, in which each fluke is composed of three segments.