Introduction to Cephalopods

Cephalopods are a remarkable class of molluscs. Over hundreds of millions of years, they have evolved from slug-like ancestors into the even more complex animals we are familiar with today, perhaps from video footage, our plates, or — if we are lucky — personal observations from aquaria or the ocean. Their eyes, appearing so similar to those of vertebrates, seem familiar… yet also alien. What would it be like to interact with the world through so many soft arms, lined with suckers that can taste as well as feel and grip? Or to change our entire body shape, texture and colour several times within a single second? We can barely imagine–but we are fascinated.

Diversity

Most living cephalopods fall into one of four main groups: squids (Teuthida; 400+ species), octopuses (Octopoda; ~300+ species), cuttlefishes (Sepiida; 120+ species), and ‘bobtail’ or ‘dumpling’ squids (Sepiolida; 70+ species). Less diverse, but equally fascinating, are the bathyteuthids (Bathyteuthida; ~10 species, such as the ‘comb-fin squids’), ‘pygmy squids’ (Idiosepiidae, ~8 species), nautiluses (Nautilida; 6 species), and vampyromorphs (Vampyromorpha; 1 species).

Once built, a link will appear here to the interactive Cephalopod Evolutionary Tree

Ecology

All known cephalopods are carnivorous apart from the vampire ‘squid’ (Vampyroteuthis infernalis), which is largely a detritivore. Predatory cephalopods hunt using a variety of strategies and features that often includes excellent vision and rapid swimming / striking movements, and may (depending on the group) also include camouflage, mesmerisation of prey, lures, ambush tactics, hooks/claws, and suckers (in some extreme cases, there are thousands of microscopic, super-sticky suckers). Some evidence suggests that large cephalopods may fill in ecological niches left vacant by overfished finfish species, and that this trend may increase with further human impacts on the oceans, including climate change. Cephalopods are themselves important food sources for a wide variety of other animals including apex predators such as seabirds, pinnipeds, cetaceans and finfishes, as well as other cephalopods (cannibalism is common in some species), crustaceans, and other invertebrates. Some species of cephalopods gather in large reproductive groups, dying off en masse when spawning (or brooding) is complete, providing large pulses of organic carbon to the sea floor.

Zoogeography

Cephalopods have been observed in all marine environments, from the surface down to about 7,000m. Some species seem to stay within relatively small geographic regions, while others (such as the giant squid) are found worldwide, wherever depth and temperature are suitable. Some species complete their life cycles within a single habitat. Others may live in a particular region (or depth layer) during their early life stages, later migrating to a different location (or depth).

Human Interactions

Cephalopods have attracted human attention for millennia. These animals provide us with inspiration for stories, art, film, and technological advances, as well as food and other products. Some species are fished (many coastal octopuses and cuttlefishes, as well as squids mostly from the families Ommastrephidae and Loliginidae). Some are kept in public or home aquarium displays. Some can be commonly encountered by beachgoers, snorkellers, or divers; others have not yet been seen alive by humans, or are known only from tantalising glimpses captured by deep-sea observation technology such as remotely operated vehicles (ROVs).