Saturday, November 24, 2012

Blanket Octopus

Blanket Octopus | This is one weird open ocean octopus! It looks like the Batman symbol flying through the ocean. It's common name, Blanket octopus, comes from their large web which they use to glide through the ocean. Blanket octopuses are rarely observed, but when people see them they notice. One, complete with eggs, washed up in Bermuda while I was off island on vacation. It made the local news and was the talk of the island. Another was recently (Sept 2009) spotted in St. Thomas, USVI.

The blanket octopus (Tremoctopus violaceus) is a rarely encountered pelagic species that spends its entire life cycle in the open ocean (Norman et al. 2002). Until the first observation of a living male off the northern Great Barrier Reef, Australia (Norman et al. 2002), males were known only from dead individuals picked up in trawls and plankton nets. Like other pelagic octopus species, T. violaceus exhibits sexual size dimorphism. The degree of sexual size dimorphism in this species, however,  is extraordinary: Females may reach 2 m in length whereas the reproductively mature male collected by Norman et al. was just 2.4 cm long. Individual weights of males and females differ by a factor of at least 10,000 (Norman et al. 2002).

Tremoctopus violaceus lives in the open ocean often in deep water (120-750 m) in the Mediterranean and the North and South Atlantic Ocean. The offspring are likely planktonic given the small size of the eggs. These octopuses may reproduce more than once but no one really knows much about their life history.

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