the Colombia lowlands east of the Andes Mountain
Range and in the vicinity of the Orinoco.
Leptestheriidae
The two species of Leptestheriidae in Colombia are
not yet described. They generally inhabit ponds with
a muddy bottom. Leptestheria sp. 1 was found during
several years in only one locality, in the upper Magdalena Valley, and exclusively in parthenogenically
reproducing populations. Leptestheria sp. 2 was found
in abundant bisexual populations on the banks of the
Orinoco.
M etalimnadiidae
The one species of this monotypic family, Metalimnadia serratura Mattox, was first found in Colombia along the banks of the Orinoco in 1991 and was
described as Paraimnadia guayanensis Roessler. Elsewhere (Roessler, 1995a), I discuss the taxonomy and
synonymy of this species. Mattox (1952) described this
species based on museum material from Venezuela,
collected approximately 100 kilometers south of where
I found my samples. That site is also on the banks of
the Orinoco and I could verify that it shows the same
geological characteristics as described for my material. (A second as yet undescribed species of this family
occurs in Brazil- D. Belk, pers. com.)
Metalimnadia is an ecologically interesting form,
which was found in a special type of rock pool in the
rocky formations of the ancient Guiana Shield in the
immediate vicinity of the Orinoco. In the northern part
of South America, the Orinoco marks the approximate
western limit of the outcropping Guiana Shield, and
in Colombia the outcroppings of this formation are
relatively scarce. M. serratura seems to be specially
adapted to small rock pools, characteristic of the eroded
surface of the Guiana Shield. These very typical pools
are generally round and very shallow. The bottoms are
covered by little fragments of rocks and are typically
level. Some mud and sparse smaller vegetation may
occasionally appear, but the pools more often show
blooms of green algae rather than higher vegetation.
Metalimnadia appears in bisexual, abundant populations and is the only conchostracan species found
at the higher elevations of these rocky formations.
At lower elevations, and especially in larger, deeper ponds with muddy bottoms and higher vegetation,
M. serratura occasionally coexists with Eulimnadia,
and sometimes with Leptestheria. At the foot of the
rocky formations and in deeper clefts or enlarged fis131
sures at lower levels, this species does not survive in
competition with Eulimnadia and Leptestheria.
The contact of the rocky extensions of the Guiana
Shield with the flat Colombian lowlands or Llanos,
formed mainly by alluvial material from the eroding
Andes, constitutes a typical ecotonal condition, where
different temporary pool communities come into contact and where boundary effects lead to a high species
diversity. I found seven euphyllopod species, each
of them with a specific ecological niche, living in
varying combinations and in different and often very
small ponds within areas no larger than 600 square
meters. The species I found in these areas are Eulimnadia magdalenensis, E. colombiensis, Leptestheria sp.
2, Lynceus sp., Metalimnadia serratura, Cyclestheria
hislopi and also one Dendrocephalus species.
The specific ecological adaptation of Metalimnadia within these communities is clearly its capacity to
prosper in the rock pools at temperatures above those
that other species can tolerate. I measured temperatures
up to 44°C from the intense radiation absorbed by the
dark rocks. The very high evaporation rates of the shallow pools is compensated by refilling with water from
the surrounding rocks. These pools, then, despite their
small volume, do not dry up easily and have a relatively
long duration. This aspect is very important since the
developmental rate of Me talimnadia is slower than that
of the potentially neotenic Eulimnadia magdalenensis
and of E. colombiensis with which Metalimnadia cannot compete at lower temperatures.
Acknowledgments
The studies on conchostracans were funded by grants
from the Colombian Institute for Development of
Science and Technology 'Francisco Jose de Caldas'
(COLCIENCIAS) and the Los Andes University. I
am especially indebted to the staff of the Colombian Hydrometeorological Institute (HIMAT) for their
cooperation during several national exhibitions. I thank
Dr Denton Belk for the critical and stimulating revision of the manuscript and Trudy Sassaman for typing
and copy editing the final draft.
References
Baird, W, 1859. Description of some recent Entomostraca from
Nagpur collected by Rev. S. Hislopi. Proc. Zoo!. Soc. London
63: 231-234.
Range and in the vicinity of the Orinoco.
Leptestheriidae
The two species of Leptestheriidae in Colombia are
not yet described. They generally inhabit ponds with
a muddy bottom. Leptestheria sp. 1 was found during
several years in only one locality, in the upper Magdalena Valley, and exclusively in parthenogenically
reproducing populations. Leptestheria sp. 2 was found
in abundant bisexual populations on the banks of the
Orinoco.
M etalimnadiidae
The one species of this monotypic family, Metalimnadia serratura Mattox, was first found in Colombia along the banks of the Orinoco in 1991 and was
described as Paraimnadia guayanensis Roessler. Elsewhere (Roessler, 1995a), I discuss the taxonomy and
synonymy of this species. Mattox (1952) described this
species based on museum material from Venezuela,
collected approximately 100 kilometers south of where
I found my samples. That site is also on the banks of
the Orinoco and I could verify that it shows the same
geological characteristics as described for my material. (A second as yet undescribed species of this family
occurs in Brazil- D. Belk, pers. com.)
Metalimnadia is an ecologically interesting form,
which was found in a special type of rock pool in the
rocky formations of the ancient Guiana Shield in the
immediate vicinity of the Orinoco. In the northern part
of South America, the Orinoco marks the approximate
western limit of the outcropping Guiana Shield, and
in Colombia the outcroppings of this formation are
relatively scarce. M. serratura seems to be specially
adapted to small rock pools, characteristic of the eroded
surface of the Guiana Shield. These very typical pools
are generally round and very shallow. The bottoms are
covered by little fragments of rocks and are typically
level. Some mud and sparse smaller vegetation may
occasionally appear, but the pools more often show
blooms of green algae rather than higher vegetation.
Metalimnadia appears in bisexual, abundant populations and is the only conchostracan species found
at the higher elevations of these rocky formations.
At lower elevations, and especially in larger, deeper ponds with muddy bottoms and higher vegetation,
M. serratura occasionally coexists with Eulimnadia,
and sometimes with Leptestheria. At the foot of the
rocky formations and in deeper clefts or enlarged fis131
sures at lower levels, this species does not survive in
competition with Eulimnadia and Leptestheria.
The contact of the rocky extensions of the Guiana
Shield with the flat Colombian lowlands or Llanos,
formed mainly by alluvial material from the eroding
Andes, constitutes a typical ecotonal condition, where
different temporary pool communities come into contact and where boundary effects lead to a high species
diversity. I found seven euphyllopod species, each
of them with a specific ecological niche, living in
varying combinations and in different and often very
small ponds within areas no larger than 600 square
meters. The species I found in these areas are Eulimnadia magdalenensis, E. colombiensis, Leptestheria sp.
2, Lynceus sp., Metalimnadia serratura, Cyclestheria
hislopi and also one Dendrocephalus species.
The specific ecological adaptation of Metalimnadia within these communities is clearly its capacity to
prosper in the rock pools at temperatures above those
that other species can tolerate. I measured temperatures
up to 44°C from the intense radiation absorbed by the
dark rocks. The very high evaporation rates of the shallow pools is compensated by refilling with water from
the surrounding rocks. These pools, then, despite their
small volume, do not dry up easily and have a relatively
long duration. This aspect is very important since the
developmental rate of Me talimnadia is slower than that
of the potentially neotenic Eulimnadia magdalenensis
and of E. colombiensis with which Metalimnadia cannot compete at lower temperatures.
Acknowledgments
The studies on conchostracans were funded by grants
from the Colombian Institute for Development of
Science and Technology 'Francisco Jose de Caldas'
(COLCIENCIAS) and the Los Andes University. I
am especially indebted to the staff of the Colombian Hydrometeorological Institute (HIMAT) for their
cooperation during several national exhibitions. I thank
Dr Denton Belk for the critical and stimulating revision of the manuscript and Trudy Sassaman for typing
and copy editing the final draft.
References
Baird, W, 1859. Description of some recent Entomostraca from
Nagpur collected by Rev. S. Hislopi. Proc. Zoo!. Soc. London
63: 231-234.