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BASIC INSTINCTS
LEST YOU DOUBT the awesome power of the drive to procreate,
consider what Mr. and Mrs. Argonaut (Argonauta argo) must go
through to send baby argonauts out into the world.
This octopus species lives in open water in Earth’s tropical and
subtropical seas. It’s not the easiest place to find a mate, espe-
cially since the male is tiny—less than three-quarters of an inch
long—while the female can be up to 30 times his size. She has two
specialized dorsal arms that secrete a chalky substance, forming
a pleated shell in which she can hide, float, and brood eggs. The
male is sans shell, but he too has a specialized arm: a tentacle-like,
detachable copulatory organ called a hectocotylus.
After attaching to the female, the male releases his hectocotylus,
which worms its way into the female’s mantle cavity. She may
stockpile these disembodied sperm arms from several mates and
use them to fertilize her eggs over time. She’ll lay strings of eggs
tethered to her shell (also called an egg case) where she can tend
them as they develop. Scientists know this because they’ve been
able to observe argonaut mothers live—but not fathers.
After donating his paternal part, no male has been seen alive
growing a new one; only dead specimens have been found. As his last
act, the small but mighty paterfamilias gives an arm and a life to the
cause of reproduction. —PATRICIA EDMONDS AND EVA VAN DEN BERG
HOW DOES THIS OCEANIC ODD
COUPLE MANAGE TO HAVE SEX?
PHOTOGRAPH BY JULIAN FINN
Greater argonaut
(Argonauta argo)
- NAME GAME
This species of octopus is
also known as the paper
nautilus (the shell it builds
to hold its eggs is made of
paper-thin calcium carbon-
ate). The Chinese name for the
species translates to “white
seahorse’s nest.”
- ARGONAUT MYTH
In 300 B.C. Aristotle described
his vision of a female argonaut
using her shell as a boat and
her tentacles as sails and oars.
In 2010 octopus experts Julian
Finn and Mark Norman docu-
mented what actually occurs:
The argonaut moves by expel-
ling jets of water, surfaces
enough to trap air in her shell,
then is buoyed at an optimal
water level by the air bubble.
- COMMON, ELUSIVE
Though rarely seen by
humans, A. argo is widespread
in Earth’s more tropical oceans.
It’s preyed upon by tuna,
dolphins, and billfishes but
still described as of least
concern on the IUCN Red List
of Threatened Species.
J. FINN, MUSEUMS VICTORIA, AUSTRALIA; TAYLOR MAGGIACOMO, NGM STAFF (ILLUSTRATION)Female, 17 inches Male, 0.6 in