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P. 9. MEADOWS AND J. I. UAM2BELL
all were alive after three days, but Orconectea propinqum were not
able to burrow and half of them died within the three days. Viability
experiments showed similar effects; C. fodiens survived longer on
desiccation and at increased temperatures than did 0. propinquus.
The two species were also differentiated by their current responsesC. fodiens is able to maintain its position more successfully in fast
currents, and by their substrate preferences-C. fodiens prefers mud
while 0. propinquw prefers gravel. Even this excellent study, however,
is not complete. We hope that Bovbjerg will eventually study the two
species' temperature and humidity preferences and their responses to
calcium ions.
It is clear from this survey that animals living in fresh waters use
information from many physical and chemical variables when choosing
their habitats. Responses to contact with solid objects (thigmotaxis),
to current speed, to the nature of the bottom, and to light, are known
for a number of species, but more comparative studies are needed. On
the other hand very little is known of pressure responses, temperature
preferences, reaction to anaerobic conditions and their relation to pH,
humidity and salinity preferences, and for burrowing animals,
preferences for certain depths of sediment. Finally, we would stress
the lack of knowledge of the role of inorganic and organic ions in
solution and of the porosity and thixotropic properties of sandy sediments, and point out the need for investigations into the way
variables interact with each other to determine the most suitable
habitat of a given species.
D. Interstitial animals
The peculiar nature of the habit and habitat of animals that live
between sand grains in marine and freshwater sands has only recently
received anything but passing comment. It is a rich new world for the
taxonomist as well as for the experimental ecologist. Swedmark (1964)
considers that the space between the sand grains is the most important
factor determining the types and numbers of animals present. Almost
as important, he feels, are the granulometric characteristics of the sands,
and the continuous rearrangement that the surface layers of intertidal
and inshore sands must receive from wind, wave and currents.
Temperature, salinity and oxygen availability since they vary significantly from place to place will also be important (Swedmark, 1964;
Enckell, 1968), as will solid/liquid interfacesb ecause animals often
meet them (Faur6-Fremiet, 1950). The animals in this environment are
an odd assortment representing most invertebrate phyla; they share
the common Characteristics of small size, bizarre form and ability to
P. 9. MEADOWS AND J. I. UAM2BELL
all were alive after three days, but Orconectea propinqum were not
able to burrow and half of them died within the three days. Viability
experiments showed similar effects; C. fodiens survived longer on
desiccation and at increased temperatures than did 0. propinquus.
The two species were also differentiated by their current responsesC. fodiens is able to maintain its position more successfully in fast
currents, and by their substrate preferences-C. fodiens prefers mud
while 0. propinquw prefers gravel. Even this excellent study, however,
is not complete. We hope that Bovbjerg will eventually study the two
species' temperature and humidity preferences and their responses to
calcium ions.
It is clear from this survey that animals living in fresh waters use
information from many physical and chemical variables when choosing
their habitats. Responses to contact with solid objects (thigmotaxis),
to current speed, to the nature of the bottom, and to light, are known
for a number of species, but more comparative studies are needed. On
the other hand very little is known of pressure responses, temperature
preferences, reaction to anaerobic conditions and their relation to pH,
humidity and salinity preferences, and for burrowing animals,
preferences for certain depths of sediment. Finally, we would stress
the lack of knowledge of the role of inorganic and organic ions in
solution and of the porosity and thixotropic properties of sandy sediments, and point out the need for investigations into the way
variables interact with each other to determine the most suitable
habitat of a given species.
D. Interstitial animals
The peculiar nature of the habit and habitat of animals that live
between sand grains in marine and freshwater sands has only recently
received anything but passing comment. It is a rich new world for the
taxonomist as well as for the experimental ecologist. Swedmark (1964)
considers that the space between the sand grains is the most important
factor determining the types and numbers of animals present. Almost
as important, he feels, are the granulometric characteristics of the sands,
and the continuous rearrangement that the surface layers of intertidal
and inshore sands must receive from wind, wave and currents.
Temperature, salinity and oxygen availability since they vary significantly from place to place will also be important (Swedmark, 1964;
Enckell, 1968), as will solid/liquid interfacesb ecause animals often
meet them (Faur6-Fremiet, 1950). The animals in this environment are
an odd assortment representing most invertebrate phyla; they share
the common Characteristics of small size, bizarre form and ability to