changes finally to a bright white, caused by the total
reflection of light (Figs 2d, 4, 7).
I never observed the completion of normal development of eggs in either type of these females. Normally,
in these circumstances, both parthenogenetic as well
as diapause eggs are reabsorbed within the ovaries; or,
if they are occasionally oviposited, they die within the
brood chamber.
At present, the significance of this phenomena in
Cyclestheria can only be the object of speculation. In
modern cladocerans the production of parthenogenetic
direct-developing eggs can be switched to the production of diapause eggs, and this occurs frequently as
a reaction to special environmental conditions. Most
cladoceran females can produce parthenogenetic eggs
after the formation of ephippial eggs or continue production of diapause eggs. In the observed populations
of Cyclestheria, the described processes could be interpreted as an attempt to do that. After the formation
of parthenogenetic eggs and in adverse environmental
conditions oogenesis switches over to the development
of diapause eggs. Nevertheless, at least in the observed
populations, this process is not performed successfully
for yet unknown reasons.
An additional remark can be made about the corpuscles. The accumulation of corpuscles is not restricted to the valves but can also be found in other parts
of the body, especially within the circulatory system.
The source and nature of the corpuscles, as well as
their function are not clear. The reflection of light and
thus protection against radiation perhaps represents an
advantage as the number of individuals with hypodermic corpuscles increases during the progress of the
dry season in conjunction with increasing solar radiation.
Corpuscles of chitinous nature, sometimes very
large ones, have been reported before and in different cell types in other crustaceans (Alverdes, 1912).
Nonetheless, other corpuscles of similar shape and
in similar quantities as observed in Cyclestheria have
been identified as cysts or developmental stages of parasitic organisms, which reproduce copiously within the
circulatory system of Cladocera (Daphnia magna) and
finally induce the death of the animal by mechanical
obstruction of this system (Jirovec, 1936).
It is possible that the observed phenomena, including the production of nonviable eggs, represent consequences of metabolic difficulties caused by adverse
environmental conditions. Modern conchostracans are
freshwater forms. The drying of the habitat increases
123
temperature and salinity levels, which are possibly not
tolerated.
The formation of corpuscles is not restricted to
this species. I found this phenomenon under similar environmental conditions in other Colombian conchostracans and in cladocerans and ostracods as well.
Also in Cyclestheria, the production of corpuscles is
not restricted to parthenogenetic females, males also
undergo this morphophysiological change, apparently
without affecting their spermatogenesis (Fig. 4a). The
phenomenon can also be induced in laboratory cultures
of conchostracans by raising conductivity levels above
450 to 500 Mm h -\ and at moderated temperatures
(Roessler, unpublished data). I am still working on this
subject.
Behavior
Comments on the behavior of Cyclestheria are scarce.
Sars (1887) and Sissom (1975; 1980) made a few annotations concerning swimming movements and activity.
I found within the Colombian populations that in their
natural habitat, the species prefers to stay at a certain
depth according to temperature, solar radiation and
the prevalent type of vegetation. The animals always
can be found in close proximity to vegetation. In the
absence of vegetation they hide in mud of the bottom;
at least they do so in the marginal and well oxygenated
zones of the ponds. Here, as well as within the algae
masses or other types of vegetation, the individuals
start to secrete a mucus which forms laminar external
sheets on the surfaces of the carapace valves. The two
mucus plates join dorsally and ventrally to envelop
the carapace. The animals are ultimately enclosed in a
capsule with two openings that facilitate the continuous flow of water through the capsule, maintained by
the filtering movements of the appendages. The water
enters the anterior gap and exits though the posterior. The anterior gap also permits the extension of the
second antennae (Fig. 7).
The encapsulated animal is hidden within and
closely fixed to the vegetation or mud, so that the individual is practically undetectable. Males and sexual
females behave similarly, although the males are generally more active and can be seen moving freely in the
vegetation. I often observed accumulations of animals
of the different types, which apparently did not reflect a
corresponding resource concentration, and could have
indicated a certain type of social attraction. In this
context, I would like to speculate that sperm may be
transmitted by water currents caused by the female's
reflection of light (Figs 2d, 4, 7).
I never observed the completion of normal development of eggs in either type of these females. Normally,
in these circumstances, both parthenogenetic as well
as diapause eggs are reabsorbed within the ovaries; or,
if they are occasionally oviposited, they die within the
brood chamber.
At present, the significance of this phenomena in
Cyclestheria can only be the object of speculation. In
modern cladocerans the production of parthenogenetic
direct-developing eggs can be switched to the production of diapause eggs, and this occurs frequently as
a reaction to special environmental conditions. Most
cladoceran females can produce parthenogenetic eggs
after the formation of ephippial eggs or continue production of diapause eggs. In the observed populations
of Cyclestheria, the described processes could be interpreted as an attempt to do that. After the formation
of parthenogenetic eggs and in adverse environmental
conditions oogenesis switches over to the development
of diapause eggs. Nevertheless, at least in the observed
populations, this process is not performed successfully
for yet unknown reasons.
An additional remark can be made about the corpuscles. The accumulation of corpuscles is not restricted to the valves but can also be found in other parts
of the body, especially within the circulatory system.
The source and nature of the corpuscles, as well as
their function are not clear. The reflection of light and
thus protection against radiation perhaps represents an
advantage as the number of individuals with hypodermic corpuscles increases during the progress of the
dry season in conjunction with increasing solar radiation.
Corpuscles of chitinous nature, sometimes very
large ones, have been reported before and in different cell types in other crustaceans (Alverdes, 1912).
Nonetheless, other corpuscles of similar shape and
in similar quantities as observed in Cyclestheria have
been identified as cysts or developmental stages of parasitic organisms, which reproduce copiously within the
circulatory system of Cladocera (Daphnia magna) and
finally induce the death of the animal by mechanical
obstruction of this system (Jirovec, 1936).
It is possible that the observed phenomena, including the production of nonviable eggs, represent consequences of metabolic difficulties caused by adverse
environmental conditions. Modern conchostracans are
freshwater forms. The drying of the habitat increases
123
temperature and salinity levels, which are possibly not
tolerated.
The formation of corpuscles is not restricted to
this species. I found this phenomenon under similar environmental conditions in other Colombian conchostracans and in cladocerans and ostracods as well.
Also in Cyclestheria, the production of corpuscles is
not restricted to parthenogenetic females, males also
undergo this morphophysiological change, apparently
without affecting their spermatogenesis (Fig. 4a). The
phenomenon can also be induced in laboratory cultures
of conchostracans by raising conductivity levels above
450 to 500 Mm h -\ and at moderated temperatures
(Roessler, unpublished data). I am still working on this
subject.
Behavior
Comments on the behavior of Cyclestheria are scarce.
Sars (1887) and Sissom (1975; 1980) made a few annotations concerning swimming movements and activity.
I found within the Colombian populations that in their
natural habitat, the species prefers to stay at a certain
depth according to temperature, solar radiation and
the prevalent type of vegetation. The animals always
can be found in close proximity to vegetation. In the
absence of vegetation they hide in mud of the bottom;
at least they do so in the marginal and well oxygenated
zones of the ponds. Here, as well as within the algae
masses or other types of vegetation, the individuals
start to secrete a mucus which forms laminar external
sheets on the surfaces of the carapace valves. The two
mucus plates join dorsally and ventrally to envelop
the carapace. The animals are ultimately enclosed in a
capsule with two openings that facilitate the continuous flow of water through the capsule, maintained by
the filtering movements of the appendages. The water
enters the anterior gap and exits though the posterior. The anterior gap also permits the extension of the
second antennae (Fig. 7).
The encapsulated animal is hidden within and
closely fixed to the vegetation or mud, so that the individual is practically undetectable. Males and sexual
females behave similarly, although the males are generally more active and can be seen moving freely in the
vegetation. I often observed accumulations of animals
of the different types, which apparently did not reflect a
corresponding resource concentration, and could have
indicated a certain type of social attraction. In this
context, I would like to speculate that sperm may be
transmitted by water currents caused by the female's