Invasive crayfish

A Spotlight Specimens special for Oxford Festival of Nature

By Sancia van der Meij, Research Fellow

The White-Clawed Crayfish (Austropotamobius pallipes) is often assumed to be native in the UK, but was in fact brought across by monks in the Middle Ages from northern France

In the 1970s this was joined by a further seven invasive crayfish species from other parts of the world, but mainly from North America. Some of these species have a very restricted distribution in the UK, such as Procambarus acutus which is only known from a single pond in Windsor.

The most widespread of these is the Signal Crayfish, Pacifastacus leniusculus, which was introduced to Europe in the 1960s and reached the UK by 1975. It is now widespread in waterways around England, Wales and parts of Scotland. There are records of Signal Crayfish from all over Oxfordshire, in the River Thames, River Cherwell, canals and ponds, and they are fished for by many people as sport or food.

The Signal Crayfish is so named because of the blue-white patches on the underside of its claws, next to the finger joint. It is the easiest invasive species to identify given its large size, smooth carapace and signal spots.

The Red Swamp Crayfish (Procambarus clarkii), from North America, is an invasive species in the UK
The Red Swamp Crayfish (Procambarus clarkii), from North America, is an invasive species in the UK

There are a number of information sites to help with identification such as the UK Crayfish Hub run by Buglife. The Non-Native species website runs a recording scheme for sightings of all invasive species too. Don’t worry though, the huge Tasmanian Giant Crayfish (Astacopsis gouldi) shown in the video clip has not made it to our waterways!

Whilst increased levels of water pollution and habitat degradation, fragmentation and loss have played their part in the decline of many crayfish populations, several species are also significantly impacted by the introduction and spread of a disease known as ‘crayfish plague’, a fungal disease is carried by some  North American species.

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From worms to stars

A Spotlight Specimens special for Oxford Festival of Nature

by Imran Rahman, Research Fellow

Starfish are among the most distinctive animals found along the seashore today. Together with other well-known forms such as sea urchins, sea cucumbers and brittle stars, they belong to a major group called the echinoderms, which is characterized by a unique type of symmetry — called fivefold symmetry. This means they can be divided into five roughly equal parts.


In contrast, the closest living relatives of echinoderms are worm-like animals that have bilateral or mirror-plane symmetry, where they are divisible into mirror-image halves. It’s widely-thought that the common ancestor shared by echinoderms and other animals also had bilateral symmetry. Because they are so different to all other living animals, deciphering the evolutionary history of echinoderms, and their path from worms to stars, has proven a major challenge for scientists.

The closest living relatives of echinoderms are worm-like animals like these acorn worms Balanoglossus sp.) from Naples

Fortunately, fossils can shed light on echinoderm evolution. Echinoderms have an excellent fossil record because they possess a hard, mineralized skeleton, which greatly enhances their chances of being preserved as fossils compared to soft-bodied organisms. The first fossil echinoderms are over half a billion years old, and include extinct groups that show both bilateral and five-fold symmetry.

In addition, fossils are known that exhibit three-fold symmetry, as well as others that lack a clear plane of symmetry – they are asymmetrical. These fossils document the earliest history of echinoderms, and so could help us to better understand their evolution.

The fivefold symmetry of the starfish
The fivefold symmetry of the starfish (Randasia granulata from Madagascar)

Based on our understanding of living animals, and using modern methods for reconstructing the relationships of different species, it’s possible to infer that the early fossil echinoderms with bilateral symmetry belong at the base of the echinoderm evolutionary tree.


The next branches in the tree lead to the asymmetrical fossil groups, and these are followed by those forms that show three-fold symmetry. Lastly, we see the diversification of forms with fivefold symmetry, including species belonging to the groups that still exist today, such as the starfish.

Using the fossil record, we can therefore see a clear picture of how echinoderms evolved from worm-like organisms into star-shaped creatures.

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