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sexual differentiation, during which male and female organs grow from early rudiments to the onset of sexual maturation (as defined by different maturation stage
systems).
1.3.4 Adult Life
The sexual maturity of adult individuals culminates in the formation and storage
of functional gametes, all the associated organs (oviducal and nidamental glands in
females, spermatophoric glands and stores in males) being ready to function.
1.3.4.1 Sexual Dimorphism
In general terms, most cephalopods have adult females and males of roughly similar
sizes, sometimes with one sex distinctly larger than the other. An exception to this
general rule is the group of pelagic octopods of the families Alloposidae, Tremoctopodidae, Ocythoidae and Argonautidae, all of which have dwarf males, some with very
peculiar forms of pelagic life (e.g. obligate rafting), and with an extremely large copulatory arm that may autotomize. None of these or other pelagic species (of families
Bolitaenidae, Amphitretidae, Vitreledonellidae) have ever been cultured. However,
future attempts to culture them may provide essential biological insights.
1.3.4.2 Egg Care
True egg care is known only in incirrate octopods. In pelagic octopods, the
spawning females always keep their masses of stalked eggs, either holding them
in their arms or fixating clusters of stalked eggs on calcified structures secreted by
special integumental glands of certain arms. In Tremoctopus, a pair of egg-carrying
rods is formed by the spawning female. A bilaterally and nearly symmetric brood
case is built (and used also as a floating device) by the female Argonauta (Finn and
Norman 2010). Ocythoe is the only ovoviviparous form known; the eggs develop
while slowly descending the extremely long oviducts from where they hatch.
The different forms of egg care behaviour in the only bottom-living octopod
family (Octopodidae) are similar to the modes of egg care known in pelagic octopods: In some species, large eggs or clusters of small eggs are carried around by the
mother, whereas in the majority of octopodid species, single eggs or clusters of eggs
are glued to a solid substratum (inside a den, often represented by man-made items
like pots, bottles or car tires!) in a way reminiscent of the egg-carrying devices of
Argonauta and Tremoctopus.
The few examples of egg brooding in decabrachian cephalopods are known from
gonatid and bathyteuthid squids (Okutani et al. 1995; Seibel et al. 2005; Bush et al.
2012). It is somewhat questionable here to use the term egg care (the way it is used
for octopods, where egg care includes sucker-based manipulation and ventilation
S. von Boletzky and R. Villanueva
sexual differentiation, during which male and female organs grow from early rudiments to the onset of sexual maturation (as defined by different maturation stage
systems).
1.3.4 Adult Life
The sexual maturity of adult individuals culminates in the formation and storage
of functional gametes, all the associated organs (oviducal and nidamental glands in
females, spermatophoric glands and stores in males) being ready to function.
1.3.4.1 Sexual Dimorphism
In general terms, most cephalopods have adult females and males of roughly similar
sizes, sometimes with one sex distinctly larger than the other. An exception to this
general rule is the group of pelagic octopods of the families Alloposidae, Tremoctopodidae, Ocythoidae and Argonautidae, all of which have dwarf males, some with very
peculiar forms of pelagic life (e.g. obligate rafting), and with an extremely large copulatory arm that may autotomize. None of these or other pelagic species (of families
Bolitaenidae, Amphitretidae, Vitreledonellidae) have ever been cultured. However,
future attempts to culture them may provide essential biological insights.
1.3.4.2 Egg Care
True egg care is known only in incirrate octopods. In pelagic octopods, the
spawning females always keep their masses of stalked eggs, either holding them
in their arms or fixating clusters of stalked eggs on calcified structures secreted by
special integumental glands of certain arms. In Tremoctopus, a pair of egg-carrying
rods is formed by the spawning female. A bilaterally and nearly symmetric brood
case is built (and used also as a floating device) by the female Argonauta (Finn and
Norman 2010). Ocythoe is the only ovoviviparous form known; the eggs develop
while slowly descending the extremely long oviducts from where they hatch.
The different forms of egg care behaviour in the only bottom-living octopod
family (Octopodidae) are similar to the modes of egg care known in pelagic octopods: In some species, large eggs or clusters of small eggs are carried around by the
mother, whereas in the majority of octopodid species, single eggs or clusters of eggs
are glued to a solid substratum (inside a den, often represented by man-made items
like pots, bottles or car tires!) in a way reminiscent of the egg-carrying devices of
Argonauta and Tremoctopus.
The few examples of egg brooding in decabrachian cephalopods are known from
gonatid and bathyteuthid squids (Okutani et al. 1995; Seibel et al. 2005; Bush et al.
2012). It is somewhat questionable here to use the term egg care (the way it is used
for octopods, where egg care includes sucker-based manipulation and ventilation
S. von Boletzky and R. Villanueva