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 , ', meaning "swimmer" and , ', "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.
Anatomy
Nectocaris had a flattened, spear head-shaped body with a fleshy-flat fin running along the length of each side. However, other authors contend that the morphology of nectocaridids is contrary to what is known about cephalopod and mollusc evolution, and they cannot be accommodated within these groups, A 2025 study based on specimens of the related Nektognathus from Sirius Passet of Greenland which preserved neural tissue showed the presence of a ventral ganglion (part of the nervous system within the body cavity), a distinctive characteristic found only among arrow worms (chaetognaths) as well as other extinct Cambrian relatives like the large Amiskwia also known from the Burgess Shale, firmly placing nectocaridids in the chaetognath stem-group. Due to lack of diagnostic features, authors have not included Nectocotis to nectocaridid.
History of study
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File:USNM PAL 198667 Nectocaris pteryx Image 08.jpg|Holotype of Nectocaris, an incomplete specimen that gave rise to erroneous reconstructions
File:Nectocaris.jpg|Original (and obsolete) reconstruction based on a single, incompletely preserved, lateral specimen (left). The author of this reconstruction, based on the material then available, considered Nectocaris to bear arthropod and chordate-like features
</gallery>Nectocaris has a long and convoluted history of study. Charles Doolittle Walcott, the discoverer of the Burgess Shale, had photographed the one specimen he had collected in the 1910s, but never had time to investigate it further. As such, it was not until 1976 that Nectocaris was formally described, by Simon Conway Morris.
Because the genus was originally known from a single, incomplete specimen and with no counterpart, Conway Morris was unable to deduce its affinity. It had some features which were reminiscent of arthropods, but these could well have been convergently derived. Its fins were very unlike those of arthropods. He focused mainly on the tail and fin morphology, interpreting Conway Morris's 'gut' as a notochord – a distinctive chordate feature. was suggested to be a soft funnel, similar to the ones used for propulsion by modern cephalopods. The interpretation would push back the origin of cephalopods by at least 30 million years, much closer to the first appearance of complex animals, in the Cambrian explosion, and implied that – against the widespread expectation – cephalopods evolved from non-mineralized ancestors.
Later independent analyses questioned the cephalopod interpretation, stating that it did not square with the established theory of cephalopod evolution, and that nectocaridids should be considered incertae sedis among Bilateria. is a soft-bodied middle Cambrian animal, known from a single reported fossil specimen from the South Australian Emu Bay Shale. It is probably a junior synonym of Nectocaris pteryx. and in 2010 Smith and Caron, agreeing that Petalilium was at least a close relative of Vetustovermis (but that treating it as a synonym was premature, given the poor preservation of the Vetustovermis type), placed it with Nectocaris in the clade Nectocarididae. is an enigmatic genus of Cambrian organism known from the Haikou area, from the Maotianshan mudstone member of the Chengjiang biota. The taxon is a junior synonym of Nectocaris pteryx. neither interpretation is supported by any compelling evidence.
Some of the characters observed in Chen et al.'s (2005) study