Saturday, 25 February 2012

Blanket Octopus

Image showing a blanket octopus
Blanket Octopus
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Superfamily: Argonautoida
Family: Tremoctopodidae
Genus: Tremoctopus
Common Name: Blanket Octopus

Blanket Octopus is the common name used for the currently 4 described species of the Tremoctopus genus. Blanket octopuses live throughout the world's tropical and sub-tropical oceans, occurring from the surface to moderate depths.

Blanket Octopus Video

Blanket Octopus Species
There are four described Tremoctopus species:
  • Tremoctopus gelatus, commonly known as the Gelatinous Blanket Octopus
  • Tremoctopus robsoni
  • Tremoctopus gracilis, commonly known as the Palmate Octopus
  • Tremoctopus violaceus, commonly known as the Common Blanket Octopus or Violet Blanket Octopus
Tremoctopus gelatus is easily recognized by its gelatinous consistency and generally pale pigmentation, while the other three species are very similar and difficult to recognize. 

Blanket Octopus Description
These octopuses exhibit an extreme degree of sexual dimorphism. Females are large and muscular and may grow to over 2 meters in total length. On the other hand, males are very small, reaching a length of only 1-2 cm, not even an inch!

They are best known for their long transparent webs that connect the dorsal and dorsolateral arms of the adult females whereas the other arms are much shorter and lack webbing.

Males develop a specially modified third right arm used for storing sperm. This structure is known as the hectocotylus.

Contrary to most octopuses, the blanket octopus does not use ink to escape predators. When females are threatened, they unfurl their large net-like membranes that spread out and billow in the water, greatly increasing their apparent size.

Jump to 00:16 to see the blanket octopus in all its glory

Blanket Octopus Predators
The Mediterranean spearfish (Tetrapturus belone) and the swordfish (Xiphias gladius) are known to feed on the various tremoctopus species.

Blanket Octopus Reproduction
During mating, the hectocotylus is detached and crawls into the mantle of the female to fertilize her eggs. It is assumed that the male dies after a while. Females usually carry well over 100,000 and up to 150,000 tiny eggs which are attached to a sausage-like calcareous secretion that is held at the base of the dorsal arms. They are carried by the female until hatching occurs.

Interesting Facts
- Blanket octopuses are immune to the poisonous Portuguese man o' war (Physalia physalis). Males and immature females rip off  their tentacles and attach them to the the suckers of their dorsal arms, most probably for defensive and offensive purposes. [1]
- Tremoctopus violaceus illustrates the most extreme example of sexual size‐dimorphism in a non‐microscopic animal. Females attain sizes of up to 2 m while males are only 1-2,4 cm long. Weight ratios between the sexes are at least 10 000:1, possibly reaching up to 40 000:1. Such sexual dimorphism in size is not seen in any other animal remotely as large. [2]

References & Further Reading
- Jones EC (1963). Tremoctopus violaceus Uses Physalia Tentacles as Weapons. Science (New York, N.Y.), 139 (3556), 764-6 PMID: 17829125
- M. D. Normanab, D. Paulb, J. Finnc, T. Tregenzad (2002). First encounter with a live male blanket octopus: The world's most sexually size‐dimorphic large animal New Zealand Journal of Marine and Freshwater Research DOI: 10.1080/00288330.2002.9517126
- Pickrell, John (Aug. 12, 2003). "Walnut-Size" Male Octopus Seen Alive for First Time. National Geographic News.
- Jones, E. C. 1963. Tremoctopus violaceus uses Physalia tentacles as weapons. Science 139: 764–766.
- Thomas, R.F. 1977. Systematics, distribution, and biology of cephalopods of the genus Tremoctopus (Octopoda: Tremoctopodidae). Bulletin of Marine Science 27(3): 353-392.

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