Thursday, 20 March 2014

Life Without a Backbone

by Rob Cooper

It is a strange turn of phrase common today that having no backbone implies weakness and lack of stoicism. Whilst many of our most impressive contemporary animal species do have well developed backbones there are many critically important animals that lack such a feature. In this article I will attempt to illustrate and expose the diversity and nature of several extinct and extant species lacking said backbone and try to show why they should certainly glean more attention than they have until now.

1. The Colossal Squid 
A wonderfully accurately named animal, the colossal squid is the largest known invertebrate that has ever lived stretching to 14 meters and weighing up to half a tonne. Like all squid the colossal squid is equipped with arms and tentacles covered in suckers, but in contrast to the slightly smaller giant squid, this giant also has sharp hooks for catching large fish and bioluminescent squid species up to 1km below the waves. Once they are fully grown they are only predated regularly by sleeper sharks and sperm whales and still manage to give both predators nasty wounds with their hooks and suckers.

2. The Japanese Spider Crab
The largest member of the arthropod phylum (which includes: insects, arachnids and crustaceans) the Japanese spider crab can have a leg span of up to 3.8 metres and despite it’s rather fearsome appearance it is reported to have a rather gentle disposition. The crab acts as an omnivorous scavenger on the sea floor and like many crustaceans has very small planktonic larvae with transparent bodies and no arms or legs that floats in the water column.

3. The Japanese hornet
Sticking with the Japanese theme we move to a rather less benevolent creature; the Japanese hornet. The sting of the hornet reportedly induces the feeling of your flesh melting and releases a pheromone cocktail that attracts all the hornets in the local area. This pheromone is also used by hornets hunting bees. European bees, which have no defence against the hornets, are often slaughtered by the hive. Japanese bees however have learned to surround the hornet with their bodies and essentially cook the animal with their body heat. 

4. The bullet Ant
If the Japanese hornet wasn’t quite enough to freak you out I invite you to check out the infamous bullet ant. Why is it called the bullet ant? Well the sting of the bullet ant is, according to the schmitd sting pain index, the most painful of all stings and feels akin to being shot. Or if you prefer a slightly more vivid description… The sting is described as ‘waves of burning, throbbing, all-consuming pain that continues unabated for up to 24 hours’. This potent sting is thought to have evolved as a defence against predators that unearth the ant.

5. Anomalocaris
Delving back over 500 million years into the deep past a rather remarkable arthropod called Anomalocaris or ‘abnormal shrimp’ led the way in the evolution of large multicellular predators that would change the evolution of all future life. Anomalocaris was a truly gigantic animal in its time reaching two metres in length and probably preying on soft bodied organisms. The eyes of Anomalocaris like other ancient and modern arthropods were compound eyes and consisted of 16,000 lenses which represents some of the earliest evolved complex eyes able to tell friend from foe and discern environmental factors, which is clearly an incredibly important evolutionary step.

6. Arthropleura
The past often presents us with monolithic, giant versions of creatures we know today. Such is the case with Arthropleura, an ancient relative of millipedes and centipedes that stretched up to 2.6 metres in length and lived in the carboniferous period over 300 million years ago. The carboniferous period was characterised by huge amounts of vegetation and photosynthesis leading to a very high partial pressure of oxygen allowing arthropods such as Arthropleura to grow so large and is also responsible for many of earths current coal deposits hence the nomenclature of the period.

7. The Crown of Thorns 
Skipping forwards 300 million years in time, large invertebrates are still vitally important ecological factors. There is no better example than the mesmerizing crown of thorns star fish, so named for the hundreds of poisonous spines that covers its aboral (opposite to the oral, mouth containing, surface) surface. The crown of thorns feeds on coral polyps and can cause great damage to reefs if they gather en masse. However ecology is rarely so black and white. The crown of thorns provides a vital role in maintaining reef biodiversity by feeding on rapidly growing corals allowing slower growing corals to grow out and allow variance in reef composition. 

8. The Horse Conch
Fearsome snail is a term rarely used. However it is a term that perfectly describes the horse conch. A huge sea snail that lives of the coast of Florida in shallow waters up to 6 metres deep, the horse conch has made a name for itself by feeding on all manner of marine gastropods and arthropods. The horse conch has even been observed cannibalising younger members of the same species. The bright orange flesh of the animal is very striking and is perhaps a reminder of the incredibly diverse forms that even seemingly mundane animals such as snail have and do take.

9. Jaekelopterus
Sea scorpions such as Jaekelopterus were formidable ocean going predators from 460 to 248 million years ago. Jaekelopterus was discovered from a single 46cm long claw by Simon Braddy and Markus Poschmann of Bristol University in 2007. The full animal is estimated at 2.5 metres in length. Whilst not true scorpions, the sea scorpions were some of the largest arthropods that have ever existed and had the common feature of two large claws presumably used to catch prey such as trilobites that shared their primordial seas.

10. The Hagfish

The hagfish is a living fossil; that is a species that has existed relatively unchanged for a very long time period. The hagfish represents a period in evolutionary history just after the vertebrate skull had evolved but before the backbone had become prominent. The hagfish has a cartilaginous skeleton meaning it can literally tie itself in knots, and indeed does in order to provide enough force to tear chucks of flesh of whale carcasses that sink to the deep sea where it lives. The hagfish can produce huge amounts of slime on contact which increases in volume when exposed to water. This slime could be argued to be the most successful predatory fish repellent ever evolved as it clogs the gills of attacking fish preventing them from ‘breathing’. This is evidenced in how almost all known predators of hagfish are birds or mammals.

I hope I’ve demonstrated here that while many of vertebrates we see around us are certainly fascinating and incredibly important, aesthetically, ecologically and commercially, the invertebrates and strange missing links like the hagfish are not only crucially important to the working of our natural world but just as intriguing, beautiful and in some cases even terrifying, despite their disadvantage in size and complexity.