11
a micronektonic way of life similar to the lifestyle of adult squid (gregarious
behaviour in loliginid squids appearing only several weeks after hatching). In short,
these species have a holopelagic life cycle.
Hatchlings of benthic and nektobenthic cuttlefish (Guibé and Dickel 2011) and
sepiolids with the exception of Heteroteuthis (Hoving et al. 2008), in their turn,
have the same lifestyle as their bottom-living parents, including burying in sandy
substrata. In other words, they have a holobenthic (at times, partially demersal)
life cycle. Two exceptions to this general rule of ontogenetic lifestyle stability are
known.
The hatchlings of the idiosepiid pygmy squids are always planktonic and later
take up the peculiar quasi-benthic lifestyle of the adult animals (which rest when not
foraging, either close to the bottom, attaching themselves to the lower face of plants
and other overhanging structures, or to floating algae). This lifestyle switching is
group typical (Boletzky et al. 2005).
The hatchlings of many bottom-living octopuses (of the family Octopodidae)
start out as planktonic young animals, very similar in overall aspects to the hatchlings of pelagic octopods (e.g. Argonautidae). In contrast to the lifestyle switching
observed in these species (and in the Idiosepiidae), certain octopus species have a
life cycle without a planktonic post-hatching phase. In other words, they are holobenthic, whereas those octopodid species passing through a planktonic phase can be
called merobenthic (Villanueva and Norman 2008).
Some confusion is due to the designation larva, which is often used for planktonic
cephalopod hatchlings. It is derived from the adoption of terms proposed for newly
hatched fish (Nesis 1979), and sometimes also alludes to gastropods. As a possible
way out of the confusion, Young and Harman (1988) suggested paralarva as a
new term for young cephalopods that do not share the biotope of their adults, thus
introducing an ecological criterion.
1.3.3 Juveniles and Subadults
Depending on whether or not a paralarval phase exists, the actual juvenile phase of
the life cycle starts either at the end of the paralarval phase or (if no paralarval phase
exists) virtually at hatching. External morphological changes can be identified
in octopuses at settlement, when the paralarval phase is ending (Villanueva and
Norman 2008), such as positive allometric arm growth, the addition of new suckers,
chromatophore, iridophore and leucophore formation, the development of skin
sculptural components and a horizontal pupillary response. At the same time, octopuses appear to lose the Kölliker organs that cover the body surface and the lateral
line system analogue. These structures have not been reported for adult benthic
octopuses (Budelmann et al. 1997). A minor morphological change is the loss of
the oral denticles of the beaks. These transformations are reflected in changes in
the relative sizes of the various lobes of the paralarval and juvenile octopus brain
(Nixon and Mangold 1996). Subadults are characterized by an adult-like external
morphometry in individuals that are not yet sexually mature. This is the phase of
1 Cephalopod Biology
a micronektonic way of life similar to the lifestyle of adult squid (gregarious
behaviour in loliginid squids appearing only several weeks after hatching). In short,
these species have a holopelagic life cycle.
Hatchlings of benthic and nektobenthic cuttlefish (Guibé and Dickel 2011) and
sepiolids with the exception of Heteroteuthis (Hoving et al. 2008), in their turn,
have the same lifestyle as their bottom-living parents, including burying in sandy
substrata. In other words, they have a holobenthic (at times, partially demersal)
life cycle. Two exceptions to this general rule of ontogenetic lifestyle stability are
known.
The hatchlings of the idiosepiid pygmy squids are always planktonic and later
take up the peculiar quasi-benthic lifestyle of the adult animals (which rest when not
foraging, either close to the bottom, attaching themselves to the lower face of plants
and other overhanging structures, or to floating algae). This lifestyle switching is
group typical (Boletzky et al. 2005).
The hatchlings of many bottom-living octopuses (of the family Octopodidae)
start out as planktonic young animals, very similar in overall aspects to the hatchlings of pelagic octopods (e.g. Argonautidae). In contrast to the lifestyle switching
observed in these species (and in the Idiosepiidae), certain octopus species have a
life cycle without a planktonic post-hatching phase. In other words, they are holobenthic, whereas those octopodid species passing through a planktonic phase can be
called merobenthic (Villanueva and Norman 2008).
Some confusion is due to the designation larva, which is often used for planktonic
cephalopod hatchlings. It is derived from the adoption of terms proposed for newly
hatched fish (Nesis 1979), and sometimes also alludes to gastropods. As a possible
way out of the confusion, Young and Harman (1988) suggested paralarva as a
new term for young cephalopods that do not share the biotope of their adults, thus
introducing an ecological criterion.
1.3.3 Juveniles and Subadults
Depending on whether or not a paralarval phase exists, the actual juvenile phase of
the life cycle starts either at the end of the paralarval phase or (if no paralarval phase
exists) virtually at hatching. External morphological changes can be identified
in octopuses at settlement, when the paralarval phase is ending (Villanueva and
Norman 2008), such as positive allometric arm growth, the addition of new suckers,
chromatophore, iridophore and leucophore formation, the development of skin
sculptural components and a horizontal pupillary response. At the same time, octopuses appear to lose the Kölliker organs that cover the body surface and the lateral
line system analogue. These structures have not been reported for adult benthic
octopuses (Budelmann et al. 1997). A minor morphological change is the loss of
the oral denticles of the beaks. These transformations are reflected in changes in
the relative sizes of the various lobes of the paralarval and juvenile octopus brain
(Nixon and Mangold 1996). Subadults are characterized by an adult-like external
morphometry in individuals that are not yet sexually mature. This is the phase of
1 Cephalopod Biology