Blanket octopus
Encyclopedia
Tremoctopus is a genus of pelagic cephalopods, containing four species that occupy surface to mid-waters in subtropical and tropical oceans. They are commonly known as blanket octopuses, in reference to the long transparent webs that connect the dorsal and dorsolateral arms
of the adult females. The other arms are much shorter and lack webbing.
These species exhibit an extreme degree of sexual dimorphism
. Females may grow to over 2 metres in length whereas the tiny males are at most a few centimeters long. The males have a specially modified third right arm which stores sperm
, known as a hectocotylus
. During mating, this arm detaches itself and crawls into the mantle of the female to fertilize her eggs
. The male dies shortly after mating. The females carry over 100,000 tiny eggs that are attached to a sausage-shaped calcareous secretion held at the base of the dorsal arms and carried by the female until hatching.
These species have evolved an unusual defense mechanism: blanket octopuses are immune to the poisonous Portuguese man o' war
, whose tentacles the male and immature females rip off and use for defensive purposes. Also, unlike many other octopuses, the blanket octopus does not use ink to intimidate potential predators. When threatened, the female unfurls her large net-like membranes that spread out and billow in the water, greatly increasing her apparent size.
Cephalopod arm
A cephalopod arm is distinct from a tentacle, though the terms are often used interchangeably.Generally, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. Octopuses have eight arms and no tentacles, while squid and cuttlefish...
of the adult females. The other arms are much shorter and lack webbing.
These species exhibit an extreme degree of sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. Females may grow to over 2 metres in length whereas the tiny males are at most a few centimeters long. The males have a specially modified third right arm which stores sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
, known as a hectocotylus
Hectocotylus
A hectocotylus is one of the arms of the male of most kinds of cephalopods that is modified in various ways to effect the fertilization of the female's eggs. It is a specialized, extended muscular hydrostat used to store spermatophores, the male gametophore...
. During mating, this arm detaches itself and crawls into the mantle of the female to fertilize her eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
. The male dies shortly after mating. The females carry over 100,000 tiny eggs that are attached to a sausage-shaped calcareous secretion held at the base of the dorsal arms and carried by the female until hatching.
These species have evolved an unusual defense mechanism: blanket octopuses are immune to the poisonous Portuguese man o' war
Portuguese Man o' War
The Portuguese Man o' War , also known as the Portuguese man-of-war, man-of-war, or bluebottle, is a jelly-like marine invertebrate of the family Physaliidae...
, whose tentacles the male and immature females rip off and use for defensive purposes. Also, unlike many other octopuses, the blanket octopus does not use ink to intimidate potential predators. When threatened, the female unfurls her large net-like membranes that spread out and billow in the water, greatly increasing her apparent size.
Species
- Tremoctopus gelatus, Gelatinous Blanket Octopus
- Tremoctopus robsoni
- Tremoctopus gracilis, Palmate Octopus
- Tremoctopus violaceus, Common Blanket Octopus or Violet Blanket Octopus