Hectocotylus
As a Hectocotylus ( plural : Hectocotyli ; after ancient Greek ἑκᾰτόν (hekatón): "hundred" and κότυλος (kótulos): "bowl", "bowl") is an arm in male cephalopods that has been transformed into a reproductive organ .
Function and morphology
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Hectocotylus of a squid (left)
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and a real octopus (right)
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Hectocotyli serve to transfer the spermatophores from the male to the female during mating . Expression and position of the Hectocotyli are species-specific and essential characteristics. Usually only one arm is reshaped accordingly. In some cuttlefish and squid two Hectocotyli are formed, while they are absent in other squids, the vampire squid and the cirrus octopus .
In cuttlefish and some squids, the hectocotylus (in these cases usually one of the fourth arms) differs from the other tentacles only in a smaller number or a complete lack of suction cups . In the case of representatives of the real octopus , on the other hand, the third arm is hectocotylated, whereby the whole arm is usually modified by a groove (spermatophore groove) along the ventral side . The spermatophoric groove usually ends in a conical appendage (calamus) at the base of the often spoon-shaped widened tentacle tip ( ligula ).
The Hectocotylus either fetches the spermatophores itself (squid, cuttlefish) from Needham's pocket or they are transported by a penis-shaped extension to the base of the arm ( Octopodidae ). In the latter case, the spermatophores are transported by muscle contraction along the spermatophore groove to the ligula and deposited in the female's mantle cavity .
Special forms
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In representatives of the Argonautoidea , the expression of the Hectocotylus takes on extreme forms. In all males of this superfamily , one of the third arms is completely hectocotylated, is carried in a special fabric bag and thrown off when mating.
Allopsidae
In Haliphron atlanticus ("seven-armed octopus"), the only species in the family, the males are much smaller than the females, but do not develop any distinct dwarf forms . The right third arm is hectocotylized. It develops in a small, inconspicuous pocket near the right eye, which outwardly leads to the apparently seven-armed appearance. The Hectocotylus only unfolds from this pocket shortly before mating and is subsequently rejected by the male.
Argonautidae
The paper boats ( Argonauta ) have an extreme form of sexual dimorphism . The males are much smaller than the females and form dwarf males . The left third arm is transformed into a hectocotylus and is carried in a tissue bag under the left eye.
The exact course of the mating ritual of the paper boats is unknown. It is believed that the hectocotylus, including spermatophores, is thrown off on contact with the female and stored in her mantle cavity, where it can persist for a long time. Sometimes there are several Hectocotyli from different males in the mantle cavity of the females. Since male specimens with a regenerating Hectocotylus have never been observed, it is assumed that the males die after mating.
Ocythoidae
The only known species of this family, Ocythoe tuberculata , also trains dwarf males. The right third arm of the male is transformed into a hectocotylus and develops in a tissue sac at the base of the arm. The Hectocotylus is only released from this tissue sac shortly before mating and equipped with spermatophores. When mating, it is thrown off and remains in the female's mantle cavity. Hectocotyli from the mantle cavity of the females often show a penis-like filament. The exact course of the mating ritual is unknown.
Tremoctopodidae
This family contains only one genus ( Tremoctopus ) with four known species. The right third arm of the dwarf male is hectocotylized and develops in a tissue sac between the funnel (hyponome) and the right eye. As with the other representatives of the Argonautoidea, the Hectocotylus is shed during mating and remains in the mantle cavity of the female.
Research history
The earliest known mention of a hectocotylus probably comes from Aristotle , who notes in his Historia animalium that some have claimed that the octopus, cuttlefish, and squid have some kind of penis in one of their arms.
The name "Hectocotylus" can be traced back to the French naturalist Georges Cuvier . As early as 1827 Stefano Delle Chiaje described a supposedly parasitic worm from the mantle cavity of a female Argonauta argo as Trichocephalus acetabularis . In 1829 Cuvier added a further form from the mantle cavity of another octopod to this observation and summarized both under the new generic name Hectocotylus . He, too, interprets the strange structures as parasitic worms.
In 1842 Albert von Koelliker observed something similar in Tremoctopus violaceus . He too initially suspects a parasitic worm, but on closer analysis he has strong doubts and interprets the structures as the long sought and never found males of the corresponding species of squid. It was not until 1853 that Heinrich Müller succeeded in deciphering their true nature and interpreting them correctly. The designation as "Hectocotylus" has remained and is used today for all arms of male cephalopods that have been transformed into reproductive organs.
Individual evidence
- ↑ a b c RT Hanlon & JB Messenger: Cephalopod Behavior. 2nd Edition, Cambridge University Press, 2018, ISBN 978-0-521-89785-3 , pp 148-205, ( excerpt ).
- ↑ P. Jereb, CFE Roper, MD Norman & JK Finn (Eds.): Cephalopods of the World: An Annotated and Illustrated Catalog of Cephalopod Species Known to Date. Volume 3: Octopods and Vampire Squids , Food and Agriculture Organization of the United Nations, Rome, 2014, ISBN 978-92-5-107989-8 , pp. 22-32, ( digitized version )
- ^ MD Norman, JK Finn & FG Hochberg: Family Octopodidae d'Orbigny, 1840. In: P. Jereb, CFE Roper, MD Norman & JK Finn (eds.): Cephalopods of the World: An Annotated and Illustrated Catalog of Cephalopod Species Known to Date. Volume 3: Octopods and Vampire Squids , Food and Agriculture Organization of the United Nations, Rome, 2014, ISBN 978-92-5-107989-8 , p. 36, ( digitized version )
- ↑ a b c d e f JK Finn: Argonautoid octopods. In: P. Jereb, CFE Roper, MD Norman & JK Finn (Eds.): Cephalopods of the World: An Annotated and Illustrated Catalog of Cephalopod Species Known to Date. Volume 3: Octopods and Vampire Squids , Food and Agriculture Organization of the United Nations, Rome, 2014, ISBN 978-92-5-107989-8 , pp. 225–243, ( digitized version )
- ↑ FD Lima, LF Mendes, L. Veras, TS Leite & SMQ Lima: The Seven-arm Octopus, Haliphron atlanticus Streenstrup, 1861 (Cephalopoda, Alloposidae), in the Fernando de Noronha archipelago, Brazil. In: Check List - The Journal of Biodiversity Data , Volume 13, Number 1, 2017, pp. 1–5, ( digitized version ).
- ↑ BY Lee, SK Tan & MEY Low: Singapore Mollusca: 9. The Family Argonautidae, with a new Record of Argonauta hians (Cephalopoda: Octopoda: Argonautoidea). In: Nature in Singapore , Volume 8, 2015, pp. 15–24, ( digitized version ).
- ↑ T. Mann: Spermatophores: Development, Structure, Biochemical Attributes and Role in the Transfer of Spermatozoa. Springer Verlag, Berlin / Heidelberg / New York / Tokyo, 1984, ISBN 978-3-642-82310-7 , p. 27, ( reading sample )
- ^ R. Wagner: Memorie sulla Storia e Notomia degli Animali senza vertebre del Regno di Napoli, di Stefano Della Chiaje, Professore agginnto alla ... etc. In: Isis or Encyclopädische Zeitung , Volume 16, 1832, p. 548, ( reading sample ).
- ↑ a b A. Kölliker: Hectocotylus Argonautae D. Ch. And Hectocotylus Tremoctopodis Köll., The males of Argonauta argo and Tremoctopus violaceus D. Ch. In: Works from the Zoological-Zootomic Institute in Würzburg , Volume 2, 1849, p. 67-89, ( digitized version ).
- ↑ H. Müller: About the male of Argonauta Argo and the Hectocotylen. In: Journal for Scientific Zoology , Volume 4, 1853, pp. 1–35, ( digitized version ).
