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Topic: Colossal squid Mesonychoteuthis hamiltoni

Is part of topic Squids and octopuses

The colossal squid Mesonychoteuthis hamiltoni is reputed to attain a greater size than the giant squid (Architeuthis dux). Until two large specimens were acquired by Te Papa, few people were aware of the existence of this huge creature. Living at depths in excess of 1000 m, and temperatures near freezing in Antarctic waters, adults of this species are exceedingly rare in collections. Because the environment in which it lives has been so poorly sampled, its life history, diet and behaviour are unknown.

Unique characters

  • The tentacle club, the expanded distal portion of the tentacle, is endowed with two rows of swiveling hooks. 
  • The beaks are the largest known of any squid, exceeding those of Architeuthis dux in size and robustness.
  • The relatively short arms are endowed with a combination of hooks and suckers.
  • A total of eight adult specimens have been reported (all but two recovered from sperm whale stomachs). Juveniles are not uncommon from surface waters to ~ 1000 m depth.

This species was first described on the basis of two arm (brachial) crowns recovered from sperm whale stomach contents. Subsequently few specimens have been collected. A sub-mature female of mantle length (ML) 1.25 m was described in 1980, and two other partial specimens (brachial crowns) are in the collections of the National Museum of Natural History, Washington DC. No comprehensive description of the mature adult, male or female, has yet been prepared. The almost complete specimen was caught in 2005 and is held in the collections at the Museum of New Zealand Te Papa Tongarewa.

Recognised distribution: Cosmopolitan throughout Sub-Antarctic to Antarctic waters. Possibly extending into southern New Zealand waters.

New Zealand reports are based on analysis of stomach contents of long-distance foraging marine predators such as whales and albatross.  Beaks attributed to this species have previously been encountered in stomachs of sperm whales, Physeter macrocephalus, caught in or proximal to northernmost eastern and western New Zealand waters, from one stranded specimen on Paekakariki Beach, and one from Mahia. They are also reported from wandering albatross chick regurgitations from Antipodes Islands and Macquarie Island. However, despite these five records from local waters, and the sixth Macquarie record, none of them confirms that the species occurs here, as wandering albatross, Diomedia exulans, average in excess of 1200 km from the nest site in search of prey, and sperm whales, especially large males, undertake extensive migrations. Mesonychoteuthis beaks have been reported from sperm whale stomachs captured off California, so the whales obviously retain some beaks in the stomach for considerable periods of time.

Abundance: Scientists consider M. hamiltoni to be a major prey item of sperm whales in the Southern Ocean. Beaks comprise 14% of the numbers found in sperm whale stomachs from the Antarctic and, because of the large size of the species, this represents an estimated 77% of the biomass consumed.

Reproduction: Unknown; mature male unknown.

One method of reproduction has been proposed for a related species, Teuthowenia pellucida, but is unknown for Mesonychoteuthis hamiltoni. In Teuthowenia the male embeds spermatophores (packets of sperm) externally into the anterior half of the female's mantle. The sperm reservoirs penetrate the inner wall and release sperm into the mantle cavity, where fertilisation of mature eggs leaving the oviducal glands apparently occurs. The large, swollen nidamental glands seen in mature females suggest that the eggs are released in one or more gelatinous egg masses. Mature females produce 6000—8000 eggs of 3.0 mm maximum diameter.

Mesonychoteuthis hamiltoni lacks a hectocotylus – a specially modified arm used to transfer spermatophores to the female. As a rule, species that lack a hectocotylus have a relatively large penis, and presumably they use this organ directly to implant spermatophores hydraulically into the female.

A second intact specimen of colossal squid was caught by the New Zealand vessel San Aspiring (Sanford Ltd) while fishing for Antarctic toothfish in the Ross Sea in February 2007.

It was brought to the surface on a long-line that had been set for toothfish and was holding on to a toothfish when first seen. The crew stopped fishing and all care was taken to get it aboard and preserve it as a specimen for science. It is the most intact adult colossal squid ever caught.

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