Giant Denizens of the Deep are Molluscs!

The new squid diva is 24ft long. How does she measure up? I just happen to have data sitting on my computer to address that issue. Don’t ask...I lay awake at night thinking about the body size of marine organisms. Below is a histogram of every documented Architeuthis capture before 1997 (data are from The Search for the Giant Squid).

image2.jpgYou can see the new capture follows slightly below the average. Molluscs (clams, oysters, scallops, chitons, tusk shells, squid, octopods, nautilus, snails, slugs) are fascinating group in general with respect to body size. Body sizes vary over 12 orders of magnitude in volume from the smallest gastropods (snails and slugs; such as <0.2 mm3 Carychium nannodes, a terrestrial land snail, from North America) to the largest cephalopods (ca. 2.2 x 1011 m3 for the giant squid Architeuthis dux). Why the remarkable range in size?

As noted by Barnes et al. (1993) “Their success is probably not so much attributable to any particular special anatomical or ecological features of the group as to the extreme plasticity and adaptability of the basic molluscan body plan.” As an example to this consider, the radiation of the mollusca includes the obvious addition of an exoskeleton but also subsequent major modifications by coiling, reduction, duplication, segmentation, and in multiple independent events the ultimate loss of the shell. The phylum possesses groups with specialized neural systems and two fundamentally different respiratory systems. Most feeding styles are known from within the group, including parasitism and symbiotic mutualisms (including coral reef zooxanthellae and hydrothermal vent chemosynthetic bacteria). Reproductive biology varies from sexual dimorphism to hermaphrodism, with uniparental mating being common in some species.

text from McClain and Nekola in press

Dr. M (1729 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, a National Science Foundation supported initiative. 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. 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 (, 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. His forthcoming book, Science of the South (, connects cultural icons of South such as pecan pie with the science behind them.