Colossal Squid (Mesonychoteuthis hamiltoni)

So I've been totally obsessed with Colossal Squid since I heard that the Museum of New Zealand Te Papa Tongarewa put one on display a couple of years ago (on my birthday no less!). The Colossal Squid is the largest known invertebrate in the world; current estimates put its maximum size at 12–14 metres (39–46 feet) long. It also has the largest eyes in the animal kingdom. This species was first described in 1925 when two arms of the squid were recovered from the stomach of a sperm whale. Then for many years, very little was learned about the species as only damaged and incomplete specimens were found. In recent years, several whole specimens have been caught, mostly as a result of our fishing the deep ocean for Antarctic and Patagonian Toothfish (the latter is sold and eaten here in US under the name Chilean Sea Bass... on a side note, the Chilean Sea Bass fishery is considered unsustainable as Toothfish grow and mature very slowly. Don't order it at restaurants!)

Here's some fun facts from Wikipedia:

While little is known about the life of this creature, it is believed to hunt prey such as chaetognatha, large fish like the Patagonian toothfish and other squid in the deep ocean using bioluminescence. Based on capture depths of a few specimens, as well as beaks found in sperm whale stomachs, the adult squid ranges at least to a depth of 2200 metres, while juveniles can go as deep as 1000 metres. It is believed to be sexually dimorphic, with mature females generally being much larger than mature males, as is common in many species of invertebrates.

The squid's method of reproduction has not been observed, although some data on their reproduction can be inferred from anatomy. Since males lack an organ called a hectocotylus (a tentacle used in other cephalopods to transfer a spermatophore to the female), they probably use a penis instead, which would be used to directly implant sperm into females.

Many sperm whales carry scars on their backs believed to be caused by the hooks of Colossal Squid. Colossal Squid are a major prey item for Antarctic sperm whales feeding in the Southern Ocean; 14% of the squid beaks found in the stomachs of these sperm whales are those of the Colossal Squid, which indicates that Colossal Squid make up 77% of the biomass consumed by these whales.Many other animals also feed on this squid, including the beaked whales (such as the bottlenose whales), pilot whale, southern elephant seal, Patagonian toothfish, Pacific sleeper shark, and albatross (e.g., the Wandering and Sooty albatrosses). However, beaks from mature adults have only been recovered from those animals large enough to take such prey (i.e., the sperm whale and Pacific sleeper shark), while the remaining predators are limited to eating juveniles or young adults.

The Museum of New Zealand Te Papa Tongarewa has lots of info on the Colossal Squid and you can even build your own squid on their website!