Aspects of this topic are discussed in the following places at Britannica.
...species) are the largest living invertebrates; A. dux attains a length of more than 20 metres (60 feet), including the extended tentacles. The smallest cephalopod is the squid Idiosepius, rarely an inch in length. The average octopus usually has arms no longer than 30 centimetres (12 inches) and rarely longer than a metre (39 inches). But arm spans of up to nine metres...
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