Just Science #1: What Is The World’s Largest Invertebrate?

Just Science Entry #1

Kim didn’t miss much. She went into Final Jeopardy with $15,000 and won the match by a scant $1 by correctly identifying the world’s largest invertebrate (answer: “What is a giant squid?”).

But was she right?

There seems to be considerable debate about this.

Steve O’Shea (giant invertebrate expert extraordinaire) says this (with his permission)…

Architeuthis is frequently reported to attain a total length of 60 ft. The largest specimen known washed ashore on a New Zealand beach, Lyall Bay (Wellington) in the winter of 1887. It was a female and “in all ways smaller than any of the hitherto-described New Zealand species” (Kirk 1887); it measured 55 feet 2 inches in total length, exaggerated by great lengthening (stretching like rubber bands) of the very slight tentacular arms; its mantle length was 71 inches (1.8 m). A comparable-sized female (ML 1.8 m) measured post mortem and relaxed (by modern standards) would have a total length of ~ 32 feet.
Mantle length (as opposed to total length) is the standard measure in cephalopods. Architeuthis is not known to attain a mantle length in excess of 2.25 m. Standard Length (SL) is the length of a squid excluding the tentacles; in Architeuthis this measure very rarely exceeds 5 m. The rest of the animal’s length, to a total length of 13 m, is made up of the two long tentacles. Of 121 specimens that we have examined, none has exceeded this figure

But wait, what about the Colossal Squid?

No mature Mesonychoteuthis hamiltoni is known. Based on the size of beaks recovered from sperm whale stomach contents it is estimated that it attains a mantle length of 2–4 m, which would render it considerably larger than Architeuthis.

An online forum challenges O’Shea’s assumption…and O’Shea responds.

So it appears that for mantle length (and mass) M. hamiltoni make take the prize. If you use total length (mantle plus tentacles) A. dux may be longer.
I agree with O’Shea in his own words…

I’ll ask you. What would you sooner be in the water with. A 13m Architeuthis (total length) weighing 275kg, or a 5m (total length) SUBMATURE Mesonychoteuthis weighing ~ 300kg? That weight has to be distributed somewhere, and that is in the BODY of the animal; it is stuffing enormous. It doesn’t have pathetic, feeble tentacles to stretch out like Architeuthis; this animal attains a massive size that exceeds that of Architeuthis in mantle and standard length.

Dr. M (1801 Posts)

Craig McClain is the Executive Director of the Lousiana University Marine Consortium. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Additionally, Craig is obsessed with the size of things. Sometimes this translated into actually scientific research. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (http://deepseanews.com/), a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.