In my previous post I explored various aspects of the Cambrian period, and briefly covered Anomalocaris. However, there are several other weird and wonderful species that are characteristic of the Cambrian.
Size Comparison
NB Anomalocaris is shown here to be larger than now thought (Lerosey-Aubril & Pates, 2018)
Opabinia
Like Anomalocaris, Opabinia would have moved around the Cambrian seas by undulating the lobes on the sides of its body. However, Whittington (1975) proposed that these lobes could have also been used to crawl along the seabed as well as for swimming slowly, as he thought the lobes were not flexible enough to allow the whole body to undulate.
To feed, it would have used its flexible, tube-like proboscis (which accounted for one third of its total body length) to catch prey – possibly to grasp worms out of their sand burrows on the seabed.
Its five eyes on short stalks could have allowed Opabinia to be on the lookout for predators.
In 1930, George Evelyn Hutchinson depicted Opabinia as swimming upside down (see image) – in fact, the same mishap has occurred with our next Cambrian creature, Hallucigenia.
Hallucigenia
It is thought that Hallucigenia used its clawed legs to hang onto and and feed on sponges such as Vauxia. Its distinctive spines would have served as protection from predators.
As shown below, in the 1970s its spines were thought to be stilt-like legs, and its legs were thought to be tentacles!
Hallucigenia may have had a hydrostatic skeleton, like modern starfish or arachnids. This means it would have been able to move its appendages through hydraulics, by altering the pressure of the fluid inside.
In addition, what was thought to be its bulbous head is now considered to be decay fluids leaked during decomposition.
It had a pair of simple eyes and a mouth with radial teeth.
Wiwaxia
Wiwaxia was covered in rows of overlapping armoured scales or plates called sclerites. These scales led palaeontologists to believe it to be an annelid (a type of scale worm). However, it is now thought to be a shell-less mollusc, as its unprotected underside resembles that of molluscs – such as that of snails.
It had long dorsal spines made of a biopolymer to protect it from predators. These were not present in juveniles, but developed as it matured. They were able to be replaced if lost.
Its mouthparts were likely used to scour the microbial mat on the seabed for microorganisms. Changes to this food source eventually caused Wiwaxia’s extinction.
The Cambrian Substrate Revolution
This is the process by which small burrowing organisms allowed anoxic sediment underneath the microbial mats to be exposed to oxygen.
The Cambrian Substrate Revolution could have been a result of the rapid diversification of species during the Cambrian Explosion, including the emergence of vertically burrowing organisms. Alternatively, it could have been a cause of this diversification.
Etymology
Opabinia regalis
Opabinia – from Opabin Pass, Yoho National Park, Canada
regalis – Latin, meaning royal or regal
Hallucigenia sparsa
Hallucigenia – from the Latin to wander in mind or go astray in thought (so-named for the creature’s “bizarre and dreamlike quality” – Simon Conway Morris)
sparsus – Latin, meaning rare or scattered
Wiwaxia corrugata
Wiwaxia – from Wiwaxy Peaks, Yoho National Park, Canada
Corrugata – from Latin, meaning wrinkled or folded
Dinosaurs and Prehistoric Animals 
