Cephalopod size
s, which include squids and octopuses, vary enormously in size. The smallest are only about long and weigh less than at maturity, while the giant squid can exceed in length and the colossal squid can weigh almost or more, making them the largest living invertebrates. Living species range in mass more than three-billion-fold, or across nine orders of magnitude, from the lightest hatchlings to the heaviest adults. Certain cephalopod species are also noted for having [|individual body parts of exceptional size].
Cephalopods were at one time the largest of all organisms on Earth, and numerous species of comparable size to the largest present day squids are known from the fossil record, including enormous examples of ammonoids, belemnoids, nautiloids, orthoceratoids, teuthids, and vampyromorphids. In terms of mass, the largest of all known cephalopods were likely the giant shelled ammonoids and endocerid nautiloids, though perhaps still second to the largest living cephalopods when considering tissue mass alone.
Cephalopods vastly larger than either giant or colossal squids have been postulated at various times. One of these was the St. Augustine Monster, a large carcass weighing several tonnes that washed ashore on the United States coast near St. Augustine, Florida, in 1896. Reanalyses in 1995 and 2004 of the original tissue samples—together with those of other similar carcasses—showed conclusively that they were all masses of the collagenous matrix of whale blubber.
Giant cephalopods have fascinated humankind for ages. The earliest surviving records are perhaps those of Aristotle and Pliny the Elder, both of whom described squids of very large size. Tales of giant squid have been common among mariners since ancient times, and may have inspired the monstrous kraken of Nordic legend, said to be as large as an island and capable of engulfing and sinking any ship. Similar tentacled sea monsters are known from other parts of the globe, including the Akkorokamui of Japan and Te Wheke-a-Muturangi of New Zealand. The Lusca of the Caribbean and Scylla in Greek mythology may also derive from giant squid sightings, as might eyewitness accounts of other sea monsters such as sea serpents.
Cephalopods of enormous size have featured prominently in fiction. Some of the best known examples include the giant squid from Jules Verne's 1870 novel Twenty Thousand Leagues Under the Seas and its various film adaptations; the giant octopus from the 1955 monster movie It Came from Beneath the Sea; and the giant squid from Peter Benchley's 1991 novel Beast and the TV film adaptation of the same name.
Due to its status as a charismatic megafaunal species, the giant squid has been proposed as an emblematic animal for marine invertebrate conservation. Life-sized models of the giant squid are a common sight in natural history museums around the world, and preserved specimens are much sought after for display.
Size in teuthology
Mantle length
Mantle length is the standard size measure for coleoid cephalopods and is almost universally reported in the scientific literature. The mantle is the cephalopod's "body", lying posterior to the head and enclosing the visceral mass and mantle cavity, the latter being used for locomotion by jet propulsion. Unless otherwise indicated, mantle length is measured dorsally over the midline of the mantle. It is a straight-line measure, not measured over the curve of the body. In Decapodiformes, mantle length is measured from the anterior edge of the mantle, to the posterior end of the mantle or the apex of the united fins, whichever is longer. In Octopodiformes, the anterior edge of the mantle is not clearly delimited dorsally due to advanced head–mantle fusion, and mantle length is therefore taken from the midpoint between the eyes to the posterior end of the mantle. When ventral mantle length is meant instead of dorsal this is always specified as such and abbreviated VML.As an indication of overall size, mantle length is generally considered more reliable than total length because cephalopod limbs may easily be stretched beyond their natural length and are often damaged or missing in preserved specimens. Nevertheless, mantle length is not equally applicable to all species. Certain benthic octopuses such as Callistoctopus ornatus are able to elongate and retract their mantles and therefore mantle length measurements, even when taken from a live specimen, may vary considerably. Another problematic case is that of the gelatinous cirroteuthids, whose weakly muscled mantles are prone to substantial shrinkage during preservation. The interocular distance may be a more reliable standard for this group.
Total length
Total length is measured along the dorsal midline with the limbs outstretched and in line with the body axis. It is the greatest measurable extent of a specimen from the posterior end of the mantle or fins to the apex of the longest limb. It is recommended that arms and tentacles be measured in a relaxed state so as not to exaggerate their length, but historically this practice was not always followed and some of the more extreme published giant squid measurements have been attributed to artificial lengthening of the tentacles. Although total length is often mentioned in relation to the largest cephalopod species, it is otherwise seldom used in teuthology. As with mantle length, it is a straight-line measure.Total length is not to be confused with arm span—also known as arm spread, radial span, or radial spread—which may be much larger and is often reported for octopuses. In squids, total length is inclusive of the feeding tentacles, which in some species may be longer than the mantle, head, and arms combined.
A related measure is standard length, which is the combined length of the mantle, head, and arms, excluding the often long feeding tentacles. This measure is particularly useful for species such as the giant squid, where almost the entire bulk of the animal takes up less than half of its total length.
Mass
Mass is reported far less frequently than either mantle or total length, and accurate records do not exist for all of the large cephalopod species. It can also vary widely depending on the state of the specimen at the time of weighing.Methods of size determination
In contrast to the vast majority of living cephalopods, which are wholly soft-bodied, size determination of the [|few surviving shelled species] is comparatively straightforward and can be accomplished with a high level of precision. Whatever the type of cephalopod, in the absence of whole specimens, size can often be estimated from only partial remains. For example, cephalopod beaks can be used for mantle length, total length and body mass estimation, and this method has notably been used to estimate the maximum size of the colossal squid. The lower rostral length of the beak is often used for this purpose. The rostral length of the lower and upper beaks is the standard measure of beak size in Decapodiformes; hood length is preferred for Octopodiformes.Mantle length has been estimated from video recordings of squid in the wild.
Early life stages
Hatchlings
Hatchlings of Idiosepius thailandicus, possibly the smallest extant cephalopod species at maturity, have a mantle length of around. The closely related Idiosepius pygmaeus weighs only upon hatching and increases in weight to as it reaches maturity in 50 days. Even smaller are the hatchlings of the commercially important Illex illecebrosus, with a mass of. Hatchlings of the giant Pacific octopus —one of the two largest octopus species—weigh on average.At the other extreme are nautiluses, which upon hatching typically have a [|shell diameter] of or more, the largest hatchling size among extant invertebrates. Hatchlings of Nautilus belauensis, one of the larger species, are estimated to weigh on the order of and mature at around after almost 4000 days, or around 11 years.
Smallest adult size
The smallest adult size among living cephalopods is attained by the so-called pygmy squids, Idiosepius, and certain diminutive species of the genus Octopus, both of which weigh less than at maturity. Idiosepius thailandicus is perhaps the smallest of all, with females averaging in mantle length and males. Average wet weights are around, respectively.Other tiny species include members of the bobtail squid family Sepiolidae; the myopsid squid genera Australiteuthis and Pickfordiateuthis; the oegopsid squid genera Abralia and Abraliopsis; the pygmy cuttlefish Sepia pulchra; and the ram's horn squid, Spirula spirula.