uptake of DOC, suspension feeding, grazing, deposit feeding, predation, symbiosis
and parasitism (Goldstein 2003). Suspension feeding is common mainly in pelagic
forms, but it is worth noting that they do not have mechanism for creating water
currents as ostracods do, thus, Foraminifera are probably less efficient as ‘passive’
suspension feeders. The pseudopodia of carnivorous species are adapted for capturing prey. Many Foraminifera are not strictly carnivorous, but utilise some other
feeding strategies. Several species lead a parasitic mode of life, for example on
bivalve molluscs, sponges, stone corals, or even other foraminiferans as a host.
Symbiotic relationships in the Foraminifera include algal endosymbiosis, chloroplast husbandry (kleptoplastidy) and bacterial endosymbiosis. In general, the
symbiont supplies the foraminifer with organic nutrition, and the host, in return,
provides the symbiont with a fairly stable microenvironment and with other compounds (dissolved nitrogen, phosphorus, etc.) (Goldstein 2003). Possessing endosymbionts is a beneficial adaptation in colonisation of new habitat. Foraminifera
in a symbiotic relationship have independent source of organic carbon, although the
majority of symbionts are light dependent.
Eukaryotic protozoans acquire food by way of endocytic uptake and subsequent
intracellular digestion within a discontinuous system of vacuoles. Bowser et al.
(1985) in their experiment on Allogromia species observed that the cytoplasm
contains only discrete vacuoles, and there is no evidence for a presence of ‘primitive gut’ or lacunary system. During their experiments some of observed vesicles
broke, which Bowser et al. (1985) inferred was due to hypo-osmotic shock. It
appears that similar looking vacuoles may be involved in diverse physiological
processes.
The best feeding strategy for the colonisation of a new habitat would appear to be
generalist omnivory and detritivory, so that organisms will find food in every aquatic
habitat. Indeed, the survival of first ostracod freshwater invaders may have been
dictated by their feeding strategy. In the Pennsylvanian Coal Measures of northern
England Carbonita, thought to be a deposit feeder, was interpreted as better adapted
and more successful in its freshwater invasions than Geisina (filter feeder) (Bless and
Pollard 1973; Bennett 2008). Both groups, Foraminifera and Ostracoda, include
omnivorous and detritivorous species. Feeding strategy was unlikely to be a barrier
for the efficient colonisation of fresh water in either of these taxa.
3.2 Osmoregulation
The majority of marine ostracods appear to be isotonic with ambient sea water, but
all freshwater forms must be osmoregulators. In inland waters organisms are
hyperosmotic regulators, while dwellers of hyperhaline environments must be hypoosmotic regulators (Lockwood 1962).
The freshwater medium is hypotonic to body fluids, so ostracods need to take up
salt from their food and/or absorb salts in their antennal glands. Embryos utilise
special cells located in the non-calcified zone of the inner valve layer for salt
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A. Iglikowska and J. Pawłowska
and parasitism (Goldstein 2003). Suspension feeding is common mainly in pelagic
forms, but it is worth noting that they do not have mechanism for creating water
currents as ostracods do, thus, Foraminifera are probably less efficient as ‘passive’
suspension feeders. The pseudopodia of carnivorous species are adapted for capturing prey. Many Foraminifera are not strictly carnivorous, but utilise some other
feeding strategies. Several species lead a parasitic mode of life, for example on
bivalve molluscs, sponges, stone corals, or even other foraminiferans as a host.
Symbiotic relationships in the Foraminifera include algal endosymbiosis, chloroplast husbandry (kleptoplastidy) and bacterial endosymbiosis. In general, the
symbiont supplies the foraminifer with organic nutrition, and the host, in return,
provides the symbiont with a fairly stable microenvironment and with other compounds (dissolved nitrogen, phosphorus, etc.) (Goldstein 2003). Possessing endosymbionts is a beneficial adaptation in colonisation of new habitat. Foraminifera
in a symbiotic relationship have independent source of organic carbon, although the
majority of symbionts are light dependent.
Eukaryotic protozoans acquire food by way of endocytic uptake and subsequent
intracellular digestion within a discontinuous system of vacuoles. Bowser et al.
(1985) in their experiment on Allogromia species observed that the cytoplasm
contains only discrete vacuoles, and there is no evidence for a presence of ‘primitive gut’ or lacunary system. During their experiments some of observed vesicles
broke, which Bowser et al. (1985) inferred was due to hypo-osmotic shock. It
appears that similar looking vacuoles may be involved in diverse physiological
processes.
The best feeding strategy for the colonisation of a new habitat would appear to be
generalist omnivory and detritivory, so that organisms will find food in every aquatic
habitat. Indeed, the survival of first ostracod freshwater invaders may have been
dictated by their feeding strategy. In the Pennsylvanian Coal Measures of northern
England Carbonita, thought to be a deposit feeder, was interpreted as better adapted
and more successful in its freshwater invasions than Geisina (filter feeder) (Bless and
Pollard 1973; Bennett 2008). Both groups, Foraminifera and Ostracoda, include
omnivorous and detritivorous species. Feeding strategy was unlikely to be a barrier
for the efficient colonisation of fresh water in either of these taxa.
3.2 Osmoregulation
The majority of marine ostracods appear to be isotonic with ambient sea water, but
all freshwater forms must be osmoregulators. In inland waters organisms are
hyperosmotic regulators, while dwellers of hyperhaline environments must be hypoosmotic regulators (Lockwood 1962).
The freshwater medium is hypotonic to body fluids, so ostracods need to take up
salt from their food and/or absorb salts in their antennal glands. Embryos utilise
special cells located in the non-calcified zone of the inner valve layer for salt
98
A. Iglikowska and J. Pawłowska