Nectocaris

Nectocaris is a genus of squid-like animal known from the Cambrian period. The initial fossils were described from the Burgess Shale of Canada. Other similar remains possibly referrable to the genus are known from the Emu Bay Shale of Australia and Chengjiang Biota of China. 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"). Two morphs are known: a small morph, about an inch long, and a large morph, anatomically identical but around four times longer. Nectocaridids had controversial affinities before 2025. Some authors have suggested that they represent the earliest known cephalopods. However, their morphology is strongly dissimilar to confirmed early cephalopods, and thus their affinities to cephalopods and even to molluscs more broadly are rejected by many authors. Their affinities to any animal group beyond Bilateria were long considered uncertain, until a 2025 study, which interpreted them as relatives of modern chaetognaths (arrow worms).