Know your Cephalopods

Art by Mark Belan Illustration — with Pablo Razdrokin.

ORDER OCTOPODAE 

Members of order Octopodae have eight arms. Evolutionary trend in Cephalopods has seen a decrease in shell size in , to which Octopodae has completely lost. 

Octopodae have eight arms lined with two rows of suckers. The suckers contain cavities (A) that create low pressure effects to ensure a tight grip on prey. 

Octopodae eat crustaceans with tough exoskeletons. As a result, their beaks contain shorter upper mandibles to better pierce their prey and inject digestive juices. 

ORDER TEUTHIDAE 

Decapodiformes include species with ten limbs (8 arms and 2 tentacles). Squid are cephalopods of the order Teuthidae and are the most diverse order of cepha-lopods with 300+ species. 

Teuthidae have two tentacles that are longer than the rest of their eight arms. The clubbed ends are the location of unique stalked suckers that are used for hunting. The eight arms also lined (2-4 rows) of these suckers. Sucker cavities can be lined with a serrated ring (B) to allow better grip for feeding on prey. 

Teuthidae normally eat soft, fleshy prey like fish and shrimp. As a result, they have elongated and tapered upper mandibles ideal for tearing prey apart. 

ORDER SEPIIDAE 

Cuttlefish are decapodiformes that belong to order Sepiidae. They are unique to other cephalopods in that they contain an internal shell known as a cuttlebone.

Sepiidae also have two tentacles separate from their eight arms that are retractable. They tend to have large, stalked suckers that are more densely populated than the 4 rows on the arms. The arms tend to be denticulated and shorter, often with only 4 rows of stalked suckers. They often do not have serrated edges (C). 

Sepiidae, like Teuthidae, also have tapered mandibles for tearing apart soft prey. The lower mandibles may also be tapered to increase accuracy in picking at smaller prey. 

ORDER NAUTILIDAE 

Nautilidae are unique cephalopods in that they contain external shells and are the only extant organisms of their order. They are the most closely related to extinct cephalopods. 

Nautilidae have 90+ tentacles that do not contain suckers. Instead, they have thin cirri that are retractable into a thicker portion called a sheath. Tiny ridges on the retractable cirrus (D) allow Nautilidae to grip their prey. 

Nautilidae beaks are similar to Octopodae in that they have a sharp, but short, upper mandi-ble ideal for piercing shielded prey.