Octopuses and squids are cephalopods, marine animals characterized by prominent heads and arms or tentacles. They are frequently confused, leading to questions about their distinctions, particularly regarding size. This article explores general size differences, the dimensions of their largest members, and how scientists measure them.
General Size Differences
Squids generally exhibit a wider range of sizes compared to octopuses, with many species tending to be larger on average. Common squid species typically measure around 60 centimeters (2 feet) in length, with some reaching up to 1.5 meters (5 feet) including tentacles.
Octopuses, while diverse, typically have a more compact body plan. Common octopus species, such as Octopus vulgaris, usually weigh between 3 to 10 kilograms (6.6 to 22 pounds) with an arm span of about 76 to 100 centimeters (2.5 to 3.3 feet) and a mantle length of 15 to 25 centimeters (5.9 to 9.8 inches). While some octopus species are quite small, measuring less than an inch, the average octopus rarely exceeds an arm span of one meter (39 inches). This general trend indicates that squids, on average, are often longer than most octopus species.
Record Holders and Extreme Sizes
When considering the largest individuals, squids hold the records for both length and mass among invertebrates. The colossal squid (Mesonychoteuthis hamiltoni) is considered the heaviest invertebrate, with confirmed specimens weighing at least 495 kilograms (1,091 pounds) and potentially up to 700 kilograms (1,500 pounds). Its maximum total length can reach approximately 4.2 meters (14 feet), though some estimates suggest up to 10 meters (33 feet).
The giant squid (Architeuthis dux) reaches about 13 meters (43 feet) from fin tip to tentacle end. These creatures can weigh up to 275 kilograms (606 pounds), with some reports suggesting up to 900 kilograms (2,000 pounds).
Conversely, the largest octopus is the giant Pacific octopus (Enteroctopus dofleini). Adults typically weigh between 10 to 50 kilograms (22 to 110 pounds) and have an arm span of up to 4.8 meters (16 feet). The largest scientifically documented specimen had a live mass of 71 kilograms (157 pounds), with claims of larger individuals reaching 272 kilograms (600 pounds) and an arm span of 9 meters (30 feet).
Measuring Their Magnitude
Measuring the size of octopuses and squids involves different metrics, primarily due to their distinct body structures. For squids, total length (TL) is measured from the longest tentacle tip to the mantle end. However, mantle length (ML), the main body’s length excluding head, arms, and tentacles, is more consistent. ML is preferred because tentacles can stretch or detach, making TL variable.
Octopuses, lacking the long tentacles of squids, are typically measured by their arm span, which is the distance across their outstretched arms, or by their total length from the tip of the longest arm to the posterior end of the mantle. Weight is also a common and often more accurate measure for octopuses, particularly for soft-bodied organisms where length can be inconsistent due to their flexible nature.