Hectocotylus

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Hectocotylus

A hectocotylus is one of the arm

Cephalopod arm

A cephalopod arm is distinct from a Tentacle#Tentacles in invertebrates, though the terms are used often interchangeably.By definition, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends....
s of the male of most kinds of cephalopod

Cephalopod

The cephalopods are the mollusc class Cephalopoda characterized by bilateral symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of cephalopod arms or tentacles....
s that is modified in various ways to effect the fertilization of the female's eggs. It is a specialized, extended tentacle

Tentacle

Tentacles can refer to the elongated flexible organs that are present in some animals, especially invertebrates, and sometimes to the hairs of the leaves of some carnivorous plant....
used to store spermatophore

Spermatophore

A spermatophore is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation....
s, the male gamete

Gamete

A gamete is a Cell that fuses with another gamete during fertilization in organisms that sexual reproduction. In species which produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual which produces the larger type of gamete?called an ovum ?and a male produces th...
. Males generally form a new hectocotylus in each new season.

The shape of the tip of the hectocotylus has been much used in octopod systematics. In many species it is considerably elaborated.

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Encyclopedia

A hectocotylus is one of the arm

Cephalopod arm

Cephalopod

Tentacle

Spermatophore

Gamete

Seven-arm Octopus

The Seven-arm Octopus is the largest known species of octopus based on scientific records, with a total estimated length of 4 m and weight of 75 kg....
(Haliphron atlanticus), the hectocotylus develops in an inconspicuous sac in front of the right eye that gives the male the appearance of having only seven arms.

The term is also used to specifically refer to the greatly modified arm of Argonauta

Argonaut (animal)

The argonauts are a group of pelagic octopuses. They are also called paper nautiluses, referring to the paper-thin eggcase that females secrete....
and allied genera

Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
. In argonauts, the male transfers the spermatophores to the female by putting its hectocotylus into a cavity in the mantle

Mantle (mollusc)

The mantle is a significant part of the anatomy of molluscs: it is the dorsum body wall which covers the visceral mass.In many, but by no means all, species of molluscs, the Epidermis of the mantle secretes calcium carbonate and conchiolin, and creates a mollusc shell....
of the female. This mantle cavity is known as the pallial cavity. This is the only contact the male and female have with each other during copulation, and it can be at a distance. During copulation, the hectocotylus breaks off from the male. The funnel-mantle locking apparatus on the hectocotylus keeps it lodged in the pallial cavity of the female.

The name "hectocotylus" was devised by Georges Cuvier

Georges Cuvier

Baron Georges L?opold Chr?tien Fr?d?ric Dagobert Cuvier was a France natural history and zoology. He was the elder brother of Fr?d?ric Cuvier , also a naturalist....
, who first found one embedded in the mantle of a female argonaut; supposing it to be a parasitic worm

Worm

A worm is a common name given to a diverse group of invertebrate animals that have a long, soft body and no legs. There are hundreds of thousands of species of worms, 2,700 of these are earthworms....
, Cuvier gave it a generic name

Generic name

Generic name may be:*Generic name, name of a biological genus*Generic name, International Nonproprietary Name for a drug*A placeholder name, referring to nobody in particular, such as Joe Bloggs or John Q. Public...
. The hectocotyl arm was first described in the biological works of Aristotle

Aristotle

Aristotle was a Greeks philosopher, a student of Plato and teacher of Alexander the Great. He wrote on many subjects, including physics, metaphysics, Poetics , theater, music, logic, rhetoric, politics, government, ethics, biology and zoology....
, and it was widely disbelieved until its rediscovery in the nineteenth century.