Invertebrates are what many people would call ‘creepy crawlies‘. Although many are small compared to us, the habits of these animals are so interesting that some people spend their whole lives devoted to studying them!
Some types of invertebrate are found mainly on land – the insects, spiders, millipedes and scorpions, to name but a few. Others, such as crabs, lobsters, sea snails, corals and many microscopic life forms require a more watery habitat. Invertebrates are found everywhere!
Take a closer look and see what we have in our collections…
Molluscs are a familiar sight in gardens, on the beach, and on our plates. The most easily recognisable are the snails with their typical coiled shell, and the bivalve molluscs such as mussels and scallops which are often served up in seafood restaurants.
Slugs are molluscs although they have no external shell. Squid, octopi and cuttlefish also lack an external shell and are supported by internal structures like the cuttlefish’s ‘cuttlebone’ or the ram’s horn squid’s coiled shell.
Molluscs can grow much larger in the oceans than they do on land. The largest known invertebrate, the colossal squid, may grow to over 14 metres long. We don’t have one of these in our collections although we do have some of its smaller cousins including the ram’s horn squid. Another very large mollusc is the giant clam, which can reach 200 kg in weight and live for 100 years.
RAMM’s shell collections
The attractive external shells of land and aquatic molluscs have attracted many a Victorian collector and we have some beautiful examples in our collections. The majority have been preserved as dry specimens and many are in still in the original boxes the collectors and original curators lovingly stored them in. The Linter collection is one such example and was donated to the Museum in 1909. It comprises 46 drawers of land and freshwater snails.
We also have Colonel George Montagu’s (1753 – 1815) shell collection. He used this collection to provide the descriptions and illustrations for one of his most important works: Testacea Britannica: a Natural history of British shells, marine, land, and fresh-water, including the most minute: systematically arranged and embellished with figures, which was published in 1803.
Voyage of HMS Blossom
Lieutenant George Peard collected shells, birds and minerals during his voyage of discovery on HMS Blossom.
On the 19th of May 1825 the HMS Blossom set sail from Spithead in Hampshire on a voyage of discovery to the Pacific Ocean and the Bering Straits. She was captained by the geographer Commander Frederick William Beechey. His mission was to explore these little known waters and to rendezvous with two other ships commanded by Captains Parry and Franklin who were conducting Arctic missions and attempting to reach the Bering Straits by new routes.
Also on board the Blossom was the naturalist George Peard who held the rank of Lieutenant. During this voyage he collected shells, birds, minerals and ethnographic objects including coins and Eskimo weapons, wherever the Blossom made port. The shells and minerals were well documented and most were identified. Peard even had a text written by the taxonomist Lamarck to help him identify the shells he found, which would have been unusual that time.
Family members, including his son who was born in Exminster, donated material from Peard’s collection to the Museum in 1916 and 1938.
Among the shells donated to RAMM are six abalone shells. The ones pictured were collected along America’s pacific coast somewhere between California and the Baja Peninsula. Others came from as far afield as the seas around Japan: Peard’s field notes mention that one particular specimen was collected on the Loochoo Islands (now known as the Ryukyu Islands) in 1827.
8 legs, 10 legs, lots of legs!
Arthropods are invertebrates with an exoskeleton, a segmented body, and jointed legs. When translated from ancient Greek, arthropod means ‘jointed foot’. RAMM has many such creatures lurking in the collections…
The insects are an astonishing group of arthropods, and perhaps the most familiar invertebrates. Please see the Insects page for more information about RAMM’s insect collection.
Arachnids – spiders and their relatives
Arachnids are arthropods with four pairs of walking legs. They also have a front pair of limbs that have been specially modified to form structures such as claws. The arachnids include spiders, scorpions, and more unusual species such as the tail-less whip scorpion.
Like insects, spiders have legs that bend at external joints. Some can float using silk as a sort of parachute, but they cannot fly. Like all arthropods, spiders must shed their exoskeleton as they grow.
There are many less well known but nonetheless fascinating cousins of spiders and RAMM has a few of these interesting specimens in its collections such as harvestmen, scorpions, ticks and the weird and exotic tail-less whip scorpions.The tail-less whip scorpion is not actually a spider or a scorpion, but a member of the Arachnid order Amblypygi.
This spider was brought in to the museum after it bit a member of the public on the ankle in his sleep.
At just under 2 cm long this is only a juvenile female tube-web spider (Segestria florentina); the patterning on her grey abdomen indicates she is not yet mature as usually adults of both sexes are almost entirely black. Adult females are among the largest spiders found in England.
As the name suggests these spiders make a tube-shaped web often in tree bark or holes in walls. The web has lines of silk radiating out from the edge that will alert the spider to the presence of small moving prey – wasps and flies are a particular favourite. When the prey triggers the trip wire the spider will dash out of the tube and capture the tasty snack with its large chelicerae (fangs). If you look closely at the chelicerae you will notice that each has a stunning stripe of iridescent green down its length.
Fancy meeting this green-fanged fiend? If so have a look in the south-facing outer walls of Exeter Cathedral. These spiders have found the perfect home in cracks and crevices where the limestone has been worn away but weathering and acidic pollution.
This tube web spider is native to western continental Europe and was introduced to Britain via ships and seaports to towns such as Exeter, Bristol and Dover about 150 years ago and are gradually spreading inland. In some walls they are so abundant that every hole is plugged with spider in its silken web. Unlike our native tube web spiders S. florentina much prefers to live in human constructions. Yet it is normally secretive and nocturnal and it will be easily frightened by human presence. However, if accidentally disturbed it will give a nasty nip that can cause pain and swelling for serveral hours or days.
For more information on biting spiders in the UK check out the Natural History Museum, London’s website.
Crustaceans – crabs, lobsters, woodlice and their relatives
Crabs, prawns and, less obviously, barnacles belong to a large group of mainly marine animals called crustacea. On land the most common crustaceans are woodlice.
Crabs have five pairs of legs which are adapted for walking, swimming, feeding and sensing. They also have branched limbs with gills for breathing. Most crustaceans live in water, where they are as abundant and successful as the insects are on land.
Horseshoe Crabs – the Limulidae
Despite their name, horseshoe crabs are not a type of crab or crustacean. These arthropods are most closely related to spiders and they are the closest living relatives of the extinct trilobites. Unusually, their blood is bright blue! It has properties that are very useful to the medical sector.
Centipedes and millipedes
Centipede and millipede are names that imply hundreds or thousands of legs. In reality centipedes have at least fifteen pairs of legs but some millipedes can have several hundred pairs.
Scutigera coleoptrata (house centipede) has 15 pairs of legs
Preserving the arthropod collection
Most of the arthropod specimens in our collections are preserved, dried and pinned in glass-topped drawers, just like the insects. These drawers have a good seal to keep out pests such as museum beetle that would feed on the specimens and destroy the collections. Some of the crabs in our collection have been preserved as wet specimens in alcohol.
Echinoderms are a group of invertebrates that includes starfish, sea urchins, feather stars, sand dollars and other related creatures. They are only found in marine environments. The name ‘Echinoderm’ literally means ‘spiny skin’ when translated from ancient Greek. These spines are particularly noticeable on live sea urchins, but they are often lost when the specimen is dried or preserved in alcohol.
RAMM’s Echinoderm collections
The majority of our Echinoderms are from Percy Sladen’s collection and are preserved as wet specimens. The fluid they are in is usually alcohol which supports the soft tissue and prevents it from decaying.
Many are stored in ground glass jars, whilst others have been placed in display jars and carefully mounted on a glass sheet in attractive patterns. Some starfish and sea urchins in our collections have been dried and are carefully stored in boxes and others are small enough to be preserved in fluid in a microscope slide.
Thanks to Sladen our collection of Echinoderms has attracted researchers from around the world. It is believed to be the largest and most comprehensive Echinoderm collection outside the Natural History Museum, London.
Sladen and HMS Challenger
Sladen had a particular interest in Echinoderms. His knowledge of these attractive creatures brought him to the attention of Sir Charles Wyville Thompson; a Scottish scientist who was in charge of the Challenger expedition. This oceanographic survey and collecting expedition took place on HMS Challenger between 1872 and 1876. Thompson asked Sladen to identify and describe the enormous wealth of Echinoderm material that was collected.