IN ITS NATIVE PACIFIC WATERS, the sea slug Siphopteron makisig
looks tiny and delicate, like a bud of colored glass. But in reality
this slug is a mirror-image mating machine, as modeled by the
pair in the photograph below.
Like most sea slug species, S. makisig is a hermaphrodite,
endowed with both male and female reproductive organs that it
uses at the same time during mating. But unlike other sea slugs,
it tops off trysts with unusually targeted stabbing.
The sex starts normally enough. To fertilize eggs developing
in each slug’s female parts, the other slug deposits sperm with its
penis. Actually, only half of its penis, which has two prongs: one
that delivers sperm with its bulbous end, and the other tipped
with a syringe-like stylet (and sometimes called hypodermic
genitalia). During the sex act, each slug stabs the other with the
stylet, which delivers prostate fluid likely bearing hormones.
Evolutionary biologist Rolanda Lange says the fluid may “increase
the fecundity of a sea slug’s own sperm, or inhibit that deposited
by previous partners.”
When other animals stab partners during sex (aka traumatic
insemination), they spear various body parts. But in a study Lange
co-authored, she identifies S. makisig as “the first known instance”
of an animal stabbing its partner between the eyes—perhaps the
better to influence the central nervous system. —EVA VAN DEN BERG
MEET A HERMAPHRODITIC SEA
SLUG THAT WIELDS A NEEDLE
DESCRIPTION
S. makisig, a marine gastro-
pod, is less than a quarter
inch long, with yellow and
red markings on its trans-
lucent white exterior. (The
blue seen here is water in
the image background.)
HABITAT
The sea slug lives on sand
beds at ocean depths from
about 20 feet to about
90 feet and commonly
nestles within micro algal
formations.
RANGE
The mollusk has been
identified in waters off
the Philippines, Australia,
and Indonesia.Siphopteron makisig sea slugs
have both female genitalia
and a double-ended penis.BIZARRE PAIRINGDIANA MARQUES, NGM STAFF. PHOTO: NILS ANTHES AND ROLANDA LANGE, UNIVERSITY OF TUEBINGEN
HeadFemale
genitaliaPenile
bulbPenile
styletFootTail
0.05
inchesIntertwined for mating, they
reciprocate sperm delivery
by extending the bulb into
the female genitalia.Then each pokes the stylet
into the other’s forehead,
injecting fluid that may
affect neural function.BASIC INSTINCTS (^) | EXPLORE