114
Conventions
In this study the term 'carapace line' is used instead
of the term 'growth line', which refers to the zone
between the borders of two subsequent outer laminas of
the conchostracan carapace. The term 'carapace line',
in contrast, refers to the outer borders of the successive
carapace plates, starting with the innermost.
The term 'larval stages' and their numerical
sequence refers to the development of the diapause
eggs starting from the time they hatch from their inflated inner egg membranes (embryonic cuticles).
Generalities
Cyclestheria hislopi is a widespread and common
species in Colombia with a clear preference for the
warm tropical lowlands. It can be found in all types of
water bodies, with the exception of the very short-term
temporary pools, where other conchostracans are common. The species appears in temporary water bodies as
parthenogenically reproducing oviparous populations,
three or four weeks after the initiation of the ecological successions and normally after the disappearance
of other conchostracans. It is also a common inhabitant of permanent waters, especially in the presence of
abundant submerged vegetation.
The parthenogenic females hatch from diapause
eggs that are enclosed within a special type of ephippium. At some point, a certain percentage of differently constituted sexual females appears within the
parthenogenetic populations. These females undergo
sexual maturation with structural changes of the carapace leading to the formation of an 'ephippium' and the
oviposition of diapause eggs. Both the parthenogenetic eggs as well as the diapause eggs develop directly,
in that Cyclestheria does not pass through free-living
naupliar or metanaupliar stages.
When certain environmental conditions prevail,
some of the females and some of the males start to
produce apparently chitinous corpuscles which accumulate in growing patches especially within the hypodermis. These females as well as some of the morphologically 'normal' ones start to produce a different egg type, which histologically resembles diapause
eggs.
All morphs in which this species may appear during different parts of the hydro-biological cycle of their
aquatic habitat form mucus capsules within the vegetation. The animals, hidden in their capsules, cannot
be seen by their enemies, and often are recognizable
only by the flow of water produced by their filtering
activity.
Parthenogenetic cycle
As far as I could determine, the advanced larval stages
hatching from the diapause eggs are always parthenogenetically reproducing females, as is common in
cladocerans (comp. Vollmer, 1912). The females start
to become sexually mature after the fourth molt after
hatching, and when they have five carapace lines. The
parthenogenetic eggs mature within the ovaries and are
deposited in the brood chamber immediately after the
fifth molt. I counted from 1 to 24 eggs, which immediately begin their direct development. The position
of the eggs apparently determines the axes of polarity
of the body after egg laying, as all embryos develop with the head attached to the epibranchial filament
as already described by Sars (1887). Modifications
of polarity seem to be important, as only the correct
position of the embryos and especially the developing
larvae within the brood chamber guarantees an adequate water circulation, once filtration movements of
the young larvae start.
Because parthenogenetic forms develop directly,
the eggs, which appear round and green, are relatively
large with a diameter of 0.24 mm. The larvae develop
and hatch entirely within the brood chamber with the
definitive number of 16 postmaxillary pairs of legs,
although the posterior extremities are still very small.
The newly hatched animals undergo two or three additional molts before being actively released from the
brood chamber by the mother, immediately before or
during her next molt at the latest. The female's molting
process is coordinated with the development and maturation of the next cohort of non-diapause eggs, and is
synchronizedwith the next oviposition. The parthenogenetic females can reproduce during their entire lifespan. Under natural conditions in Colombia, I observed
parthenogenetic females with a maximum age corresponding to 12 carapace lines.
Furthermore, the parthenogenetic cycle can be
repeated several times by the females and successive generations, so that parthenogenetic generations
constitute the most numerous part of the population
throughout the year and during the successive phases
of the hydric cycles. As a consequence, most reports
of this species refer to this special part of the life cycle
(Barnard, 1924, 1929; Nair, 1981; Sars, 1887; Dodds,
1926; Egborge & Ozoro, 1989 and others).
Conventions
In this study the term 'carapace line' is used instead
of the term 'growth line', which refers to the zone
between the borders of two subsequent outer laminas of
the conchostracan carapace. The term 'carapace line',
in contrast, refers to the outer borders of the successive
carapace plates, starting with the innermost.
The term 'larval stages' and their numerical
sequence refers to the development of the diapause
eggs starting from the time they hatch from their inflated inner egg membranes (embryonic cuticles).
Generalities
Cyclestheria hislopi is a widespread and common
species in Colombia with a clear preference for the
warm tropical lowlands. It can be found in all types of
water bodies, with the exception of the very short-term
temporary pools, where other conchostracans are common. The species appears in temporary water bodies as
parthenogenically reproducing oviparous populations,
three or four weeks after the initiation of the ecological successions and normally after the disappearance
of other conchostracans. It is also a common inhabitant of permanent waters, especially in the presence of
abundant submerged vegetation.
The parthenogenic females hatch from diapause
eggs that are enclosed within a special type of ephippium. At some point, a certain percentage of differently constituted sexual females appears within the
parthenogenetic populations. These females undergo
sexual maturation with structural changes of the carapace leading to the formation of an 'ephippium' and the
oviposition of diapause eggs. Both the parthenogenetic eggs as well as the diapause eggs develop directly,
in that Cyclestheria does not pass through free-living
naupliar or metanaupliar stages.
When certain environmental conditions prevail,
some of the females and some of the males start to
produce apparently chitinous corpuscles which accumulate in growing patches especially within the hypodermis. These females as well as some of the morphologically 'normal' ones start to produce a different egg type, which histologically resembles diapause
eggs.
All morphs in which this species may appear during different parts of the hydro-biological cycle of their
aquatic habitat form mucus capsules within the vegetation. The animals, hidden in their capsules, cannot
be seen by their enemies, and often are recognizable
only by the flow of water produced by their filtering
activity.
Parthenogenetic cycle
As far as I could determine, the advanced larval stages
hatching from the diapause eggs are always parthenogenetically reproducing females, as is common in
cladocerans (comp. Vollmer, 1912). The females start
to become sexually mature after the fourth molt after
hatching, and when they have five carapace lines. The
parthenogenetic eggs mature within the ovaries and are
deposited in the brood chamber immediately after the
fifth molt. I counted from 1 to 24 eggs, which immediately begin their direct development. The position
of the eggs apparently determines the axes of polarity
of the body after egg laying, as all embryos develop with the head attached to the epibranchial filament
as already described by Sars (1887). Modifications
of polarity seem to be important, as only the correct
position of the embryos and especially the developing
larvae within the brood chamber guarantees an adequate water circulation, once filtration movements of
the young larvae start.
Because parthenogenetic forms develop directly,
the eggs, which appear round and green, are relatively
large with a diameter of 0.24 mm. The larvae develop
and hatch entirely within the brood chamber with the
definitive number of 16 postmaxillary pairs of legs,
although the posterior extremities are still very small.
The newly hatched animals undergo two or three additional molts before being actively released from the
brood chamber by the mother, immediately before or
during her next molt at the latest. The female's molting
process is coordinated with the development and maturation of the next cohort of non-diapause eggs, and is
synchronizedwith the next oviposition. The parthenogenetic females can reproduce during their entire lifespan. Under natural conditions in Colombia, I observed
parthenogenetic females with a maximum age corresponding to 12 carapace lines.
Furthermore, the parthenogenetic cycle can be
repeated several times by the females and successive generations, so that parthenogenetic generations
constitute the most numerous part of the population
throughout the year and during the successive phases
of the hydric cycles. As a consequence, most reports
of this species refer to this special part of the life cycle
(Barnard, 1924, 1929; Nair, 1981; Sars, 1887; Dodds,
1926; Egborge & Ozoro, 1989 and others).