Nectocaris

Nectocaris pteryx is a species of possible cephalopod[2] affinity, known from the "early Cambrian" (Series 2) Emu Bay Shale and Chengjiang biota, and the "middle Cambrian" (Series 3, Stage 5) Burgess Shale.

Nectocaris was a free-swimming, predatory or scavenging organism. This lifestyle is reflected in its binomial name: Nectocaris means "swimming shrimp" (from the Ancient Greek νηκτόν, nekton, meaning "swimmer" and καρίς, karis, "shrimp"; πτέρυξ, pteryx, means "wing"). Two morphs are known: a small morph, about an inch long, and a large morph, anatomically identical but around four times longer.

Anatomy
Nectocaris had a flattened, kite-shaped body with a fleshy fin running along the length of each side.[2] The small head had two stalked eyes, a single pair of tentacles, and a flexible funnel opening out to the underside of the body.[2] The funnel often gets wider away from the head. Internally, a chamber runs along the body axis, containing a pair of gills; the gills comprise blades emerging from a zig-zag axis. Muscle blocks surrounded the axial cavity, and are now preserved as dark blocks in the lateral body.[3] The fins also show dark blocks, with fine striations superimposed over them. These striations often stand in high relief above the rock surface itself.

Diversity
Although Nectocaris is known from Canada, China and Australia, in rocks spanning some 20 million years, there does not seem to be much diversity; size excepted, all specimens are anatomically very similar. Historically, three genera have been erected for nectocaridid taxa from different localities, but these 'species' – Petalilium latus and Vetustovermis planus – likely belong to the same genus or even the same species as N. pteryx. Within N. pteryx, there seem to be two discrete morphs, one large (~10 cm in length), one small (~3 cm long). These perhaps represent separate male and female forms.