testheriidae and Lynceidae (Fig. 4). The Imnadiidae
typically present a heavy coil of thick shell material
on the egg surface, while the only described species
of Metalimnadiidae has a characteristic and relatively
thin external membrane with a network of fine ribbons
(Fig. 4 and Botnariuc & Orghidan, 1941; Roessler,
1991). On the other hand, the Colombian Leptestheriidae and Lynceidae both have a thinner outer eggshell
but their finer surface ornamentation is not easily recognizable by light-microscopy (Roessler, unpublished
data).
Eggshell features also appear distinctive in other entomostracan groups. I had the opportunity to
study these features in ostracods and certain cladocerans. In cladocerans characteristic surface ornamentation of the latent eggs (within ephippia that also have
species-specific morphologies) were described as early
as 1901 by Sars (1901). The eggshell features of different anostracans also differ morphologically (Alonso
et at., 1984; Mura et at., 1986). In the ostracod genus
Chlamydotheca and in Heterocypris bogotensis, a similar foamy basic material as in the conchostracan family Limnadiidae is deposited and, as in other species,
attains its definitive external features after egg-laying
(Roessler, 1982a, b).
Developmental morphological changes
Conchostracan development is characterized by a
sequence of stages separated by molts. The hatching
process itself can be considered as a first modified molt.
The development continues with a series of naupliar
and metanaupliar stages, and then the larvae take on
the general morphological aspects of the adult with two
valves enclosing the body. During subsequent molting
stages, new pairs of extremities are added, the head
shape changes and the valves become larger.
In the early larval stages, the molting of the valves is
complete, the young animals do not retain the external
laminas of previous stages. Typically in older individuals, the older laminas remain, overlaying the younger
and larger plates, and forming the well-known growth
lines of the typical conchostracan carapace.
The precise stage at which this transition occurs
depends on genetic and systematic considerations. At
the species level, to an extent, it varies among individuals, and, in addition, is normally influenced by
environmental conditions (Roessler, 1989, 1990).
The growth rate ofthe individuals also affects morphological features. This is especially true for the number of pairs of appendages (if this parameter is variable,
259
as, for example, in Eulimnadia), and for the number
and size of setae, spines and additional features. On the
other hand, the growth rate depends on environmental
conditions, especially temperature and such factors as
population density and food supply (Roessler, 1989,
1990).
In all cases the morphological features generally
used in classification undergo a sequence of changes
in 'normal' development and are also modulated by
environmental conditions. Therefore, it is important
to take into account the developmental stage and the
specific environmental conditions during growth of the
individual.
Within the Limnadiidae, I have reviewed morphological variability of Eulimnadia magdaienensis, a
species that is widely distributed in the Colombian lowlands, and I studied the relationship between environmental conditions, especially temperature, and certain
morphological as well as physiological features.
At 'low' temperatures, between 22 to 30 ° C, and
with an adequate food supply, growth wi11lead to large
specimens with wider growth lines. The shedding of
the laminas is extended into later stages; so that when
the individuals reach sexual maturity in the thirteenth
or fourteenth stage after hatching, they have only three
or four ample growth lines. In this family the retention
of the external laminas seems to be generally correlated
with sexual maturity (Roessler, 1989, 1990).
As temperature rises to a range from 30 to 38°C, the
individual molting processes occur faster, the respective stages and the resulting growth lines become
smaller and sexual maturity is reached earlier.
Further increases of temperatures to a range from
38 to 42 °C result in very small specimens with very
narrow growth lines that retain the younger, outer laminas. The animals enter into sexual maturity and lay
eggs in the eleventh stage after hatching. They retain
larval features, recognizable for instance by the relative size and the shape of the 'nuchal organ' (Fig. 5
and Roessler, 1990). This could be considered a phenomenon of neoteny, a condition in which individuals
retain larval characteristics into adulthood, or in this
context, sexual maturity. It seems that a very high population density has the same effect, but this aspect has
not yet been studied in detail.
This study revealed an important relationship
between environmental conditions and morphological
and physiological features (Roessler, 1990). In this
specific case, the very small specimens with neotenic
features that grew up in extremely warm, and often
very small temporary waters, almost appear to be a
typically present a heavy coil of thick shell material
on the egg surface, while the only described species
of Metalimnadiidae has a characteristic and relatively
thin external membrane with a network of fine ribbons
(Fig. 4 and Botnariuc & Orghidan, 1941; Roessler,
1991). On the other hand, the Colombian Leptestheriidae and Lynceidae both have a thinner outer eggshell
but their finer surface ornamentation is not easily recognizable by light-microscopy (Roessler, unpublished
data).
Eggshell features also appear distinctive in other entomostracan groups. I had the opportunity to
study these features in ostracods and certain cladocerans. In cladocerans characteristic surface ornamentation of the latent eggs (within ephippia that also have
species-specific morphologies) were described as early
as 1901 by Sars (1901). The eggshell features of different anostracans also differ morphologically (Alonso
et at., 1984; Mura et at., 1986). In the ostracod genus
Chlamydotheca and in Heterocypris bogotensis, a similar foamy basic material as in the conchostracan family Limnadiidae is deposited and, as in other species,
attains its definitive external features after egg-laying
(Roessler, 1982a, b).
Developmental morphological changes
Conchostracan development is characterized by a
sequence of stages separated by molts. The hatching
process itself can be considered as a first modified molt.
The development continues with a series of naupliar
and metanaupliar stages, and then the larvae take on
the general morphological aspects of the adult with two
valves enclosing the body. During subsequent molting
stages, new pairs of extremities are added, the head
shape changes and the valves become larger.
In the early larval stages, the molting of the valves is
complete, the young animals do not retain the external
laminas of previous stages. Typically in older individuals, the older laminas remain, overlaying the younger
and larger plates, and forming the well-known growth
lines of the typical conchostracan carapace.
The precise stage at which this transition occurs
depends on genetic and systematic considerations. At
the species level, to an extent, it varies among individuals, and, in addition, is normally influenced by
environmental conditions (Roessler, 1989, 1990).
The growth rate ofthe individuals also affects morphological features. This is especially true for the number of pairs of appendages (if this parameter is variable,
259
as, for example, in Eulimnadia), and for the number
and size of setae, spines and additional features. On the
other hand, the growth rate depends on environmental
conditions, especially temperature and such factors as
population density and food supply (Roessler, 1989,
1990).
In all cases the morphological features generally
used in classification undergo a sequence of changes
in 'normal' development and are also modulated by
environmental conditions. Therefore, it is important
to take into account the developmental stage and the
specific environmental conditions during growth of the
individual.
Within the Limnadiidae, I have reviewed morphological variability of Eulimnadia magdaienensis, a
species that is widely distributed in the Colombian lowlands, and I studied the relationship between environmental conditions, especially temperature, and certain
morphological as well as physiological features.
At 'low' temperatures, between 22 to 30 ° C, and
with an adequate food supply, growth wi11lead to large
specimens with wider growth lines. The shedding of
the laminas is extended into later stages; so that when
the individuals reach sexual maturity in the thirteenth
or fourteenth stage after hatching, they have only three
or four ample growth lines. In this family the retention
of the external laminas seems to be generally correlated
with sexual maturity (Roessler, 1989, 1990).
As temperature rises to a range from 30 to 38°C, the
individual molting processes occur faster, the respective stages and the resulting growth lines become
smaller and sexual maturity is reached earlier.
Further increases of temperatures to a range from
38 to 42 °C result in very small specimens with very
narrow growth lines that retain the younger, outer laminas. The animals enter into sexual maturity and lay
eggs in the eleventh stage after hatching. They retain
larval features, recognizable for instance by the relative size and the shape of the 'nuchal organ' (Fig. 5
and Roessler, 1990). This could be considered a phenomenon of neoteny, a condition in which individuals
retain larval characteristics into adulthood, or in this
context, sexual maturity. It seems that a very high population density has the same effect, but this aspect has
not yet been studied in detail.
This study revealed an important relationship
between environmental conditions and morphological
and physiological features (Roessler, 1990). In this
specific case, the very small specimens with neotenic
features that grew up in extremely warm, and often
very small temporary waters, almost appear to be a