Mollusca
Introduction:
Molluscs are soft-bodied invertebrates which lack bones or exoskeletons. The majority live in the ocean but some, such as the snails and slugs live on land, and others live in freshwater environments.
They are the largest marine phylum, compromising 23% of all named marine organisms. Molluscs are characterised by their unsegmented soft bodies, and versatile body plan- where all groups share the same basic features, which have been adapted to suit different purposes.
In the museum the molluscs can be found in the outside walled cabinets 5-7.
Structure and adaptations:
The general body plan of molluscs includes:
Mantle covering the body. This is responsible for secreting mucus and in some molluscs produces a shell
'Head' region where the mouth often contains the 'radula'- a conveyer belt of teeth on the upper mouth that drags food down
'Foot' - a muscular organ which can serve different purposes from burrowing, movement, feeding and more depending on the animal
Cavity under the mantle where respiration and excretion take place
Open circulatory system to pump blood from the gills and into the body cavity to deliver oxygen
Nervous system extending throughout the body
Most molluscs contain a mouth like structure called a radula: a conveyor belt of teeth which drags food into the mouth.
In the museum the molluscs can be found in the outside walled cabinets 5-7.
Classification:
The molluscs are separated into different groups based on the presence/absence of shells, and the type of shells they posses, among other features.
Bivalvia
Clams, oysters, mussels and scallops.
Characterised by a hinged shell which is divided into valves.
Gastropoda
Terrestrial and marine snails and slugs.
Characterised by their large foot structure used for movement crawling along substrate.
Cephalopoda
Octopus, squid, cuttlefish and nautilus
Characterised by the merging of the head + foot structures and the presence of tentacles.
Aplacophora
Worm-like marine animals with no shells. Mostly found in deep waters.
Polyplacophora
Chitons
Flattened bilaterally symmetrical molluscs which live only in marine environments. Covered in hard plating
Monoplacophora
Neopilinids
Primitive marine molluscs characterised by a single cap-shaped shell
Scaphopoda
Tusk shells
Elongated tube-like shape open at both ends.
Explore the molluscs more through the interactive phylogeny tree from One Zoom.
Museum Highlights:
Blue ringed octopus - an extremely venomous species of octopus found in the tide pools and coral reefs of he Pacific and Indian oceans, from Japan to Australia.
Male and Female argonaut- also known as Paper Nautilus. These have been separated from their shells to show the soft body
A variety of sea slug species from the Mediterranean, Pacific and UK coast. Sea slugs are renowned for their bright colours and patterns
Life history jar of a great pond snail- a large air-breathing freshwater snail that changes diet and ecology with it's different ages and habitats. For example, in habitats with poor nutrient availability it changes to a carnivorous diet
Ram's horn squid, Spirula spirula collected from Fiji on the Challenger Expedition 1872–1876
Gallery:
BIOFUELs: POLYMERASE CHAIN REACTION AND CLONING OF SELECTED CELLULASE SEQUENCES IDENTIFIED IN A METAGENOMICS LIBRARY FROM A MOLLUSC GUT. - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/General-anatomy-of-the-digestive-system-of-a-mollusc-The-digestive-tract-of-mollusc-is_fig2_277840794 [accessed 17 Nov, 2023]Aplacophora image: Monterey Bay Aquarium Research Institute Galleries. Availble from: https://www.mbari.org/team/benthic-biology-and-ecology/ Polyplacophora image: By Kirt L. Onthank, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3740595 Scaphopoda image: photo from Museum of New Zealand Collections Gallery, Available at https://collections.tepapa.govt.nz/topic/969#open-iiifViewerPhyllidiella pustulosa sea slug image: Rickard Zerpe, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons