Common blanket octopus

Mating behaviour

The third right arm in male blanket octopus is called the hectocotylus, which has a sperm-filled pouch between the arms. When the male is ready to mate, the pouch ruptures, and sperm is released into the arm. He then cuts this arm off and gives it to a female. It is likely that the male dies after mating. The female stores the arm in her mantle to be used when she is ready to fertilize her eggs. She may store several hectocotyli from different males at once.

Sexual dimorphism

The common blanket octopus exhibits one of the highest degrees of sexual size-dimorphism found in large animals. The blanket octopus exhibits remarkable sexual dimorphism, with females reaching up to 2 meters in length, while males typically remain about 2.4 cm. This size disparity is one of the most striking features of the species (Petrić et al., 2023).There are several theories as to why this developed. It is advantageous for females to be big; their large eggs take a lot of energy to maintain. The bigger a female is, the more eggs she can carry, and she can birth more offspring that could potentially survive to adulthood. Sperm does not require much energy or space to maintain, so males do not face the same pressure to be big. The use of the Portuguese man o' war tentacles is effective only in smaller animals. So selection may have favoured males to remain small in order to continue to utilize this defence mechanism.

Defense mechanisms

Predators of the common blanket octopus include the blue shark, tuna, and the billfish.

When attacked, female blanket octopuses can roll up and unfurl their webbed blanket. This makes them look bigger and may scare off predators. They can also sever the blanket to distract predators.

Additionally, female blanket octopuses have been observed with parts of Portuguese man o' war tentacles attached to their dorsal arms. It was suggested that these tentacles could serve both as defensive and offensive weapons. It is unknown how the blanket octopus obtains the tentacles or whether they are immune to the toxins in the stingers.

References

References

1. Allcock, L.. (2014). "''Tremoctopus violaceus''".
2. Sweeney, M.J. & R.E. Young (2004). [http://tolweb.org/notes/?note_id=2465 Taxa Associated with the Family Tremoctopodidae Tryon, 1879]. [[Tree of Life Web Project]].
3. (2021). "The first record of ''Tremoctopus violaceus sensu stricto'' Delle Chiaje, 1830 in southwestern Gulf of Mexico gives a hint of the taxonomic status of ''Tremoctopus gracilis''". ZooKeys.
4. "Common Blanket Octopus ''Tremoctopus violaceus''". BioLib Biological Library.
5. (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.
6. Shapiro, Leo. "Facts about Common Blanket Octopus". Encyclopedia of Life.
7. (2018). "Complete mitochondrial genome and the phylogenetic position of the pelagic octopus ''Tremoctopus violaceus'' (Mollusca: Tremoctopodidae)". Mitochondrial DNA Part B.
8. (2009). "Feeding habits of the blue shark (''Prionace glauca'') off the coast of Brazil". [[Biota Neotropica]].
9. (1998). "Cephalopods eaten by pelagic fishes in the tropical East Pacific, with special reference to the feeding habitat of pelegic fish". La mer.
10. (2019). "The Blanket Octopus and it's AMAZING Blanket!!".
11. (1977). "Systematics, distribution, and biology of cephalopods of the genus ''Tremoctopus'' (Octopoda: Tremoctopodidae)". [[Bulletin of Marine Science]].
12. (1963). "''Tremoctopus violaceus'' uses ''Physalia'' tentacles as weapons". [[Science (journal).