ANTAROTIC BENTHOS
101
It would be expected that the Antarctic fauna should contain a
high percentage of cold-water stenothermal species. The best marked
of these on the present data are as follows (known temperature ranges
in parentheses) :
Cadulus (P.) dalli antarcticus (-0.66-2.08"C);
Propeleda longicauduta (-0.66-2.08OC);
Silicula rouchi (-0m-0.40"C);
Limopsis lilliei (-0-66-2.08"C);
Philobrya sublaeuis ( -1.90-2.08"C);
Adacnarm nitens ( -1.90-1.42°C);
Lissarca notorcadensis ( -1.66-2.08"C);
Limatula hodgsoni (-1-66-2.08"C);
Pseudokellya cardifomis ( -0.66-1.37°C);
Cyclomrdia aatartoides (- 1.90-2.08°C);
Cuspidaria tenella ( -0.42-0*76"C);
Cuspidaria infelix (-0.66-2.08"C).
The ranges for a number of forms which do not reach the Antarctic
Continent may be considered for comparison. Limopsis scotiana Dell,
apparently confined to South Georgia, the South Orkneys and the
South Shetlands, has a very restricted range from -0.48 to 1~32°C.
There thus seems no reason why it could not invade Antarctic waters
from temperature considerations alone. Limopsis Airtella Rochebrune
and Mabille, found in southern South America and the Falklands, has a
range largely confined to water from 4.32 to 8.18"C while Astarte longirostri8, from the Subantarctic and South Georgia, ranges from about
4.91 to 8.30"C.
8. The Scotia Arc as a migration route
The only shallow water migration route between any other shallowwater area and the Antarctic continental shelf is through the scattered
island groups and associated shelves of the Scotia Arc. The arc is bent
right back on itself, the island groups comprising it are relatively
widely spaced, and the major hydrological phenomenon of the Southern
Ocean, the Antarctic Convergence, cuts across it. This is not to be
considered a broad highway through which whole faunas can automatically migrate. It presents a series of gaps which by combinations
of barriers of various kinds filter out families, genera and speaies selectively preventing some from reaching Antarctica, and in turn preventing some Antarctic forms from reaching South America.
Consideration of the extent to which some molluscan families
penetrate the Scotia Arc shows this selective action. A large number
A.X.B.-lO
b
101
It would be expected that the Antarctic fauna should contain a
high percentage of cold-water stenothermal species. The best marked
of these on the present data are as follows (known temperature ranges
in parentheses) :
Cadulus (P.) dalli antarcticus (-0.66-2.08"C);
Propeleda longicauduta (-0.66-2.08OC);
Silicula rouchi (-0m-0.40"C);
Limopsis lilliei (-0-66-2.08"C);
Philobrya sublaeuis ( -1.90-2.08"C);
Adacnarm nitens ( -1.90-1.42°C);
Lissarca notorcadensis ( -1.66-2.08"C);
Limatula hodgsoni (-1-66-2.08"C);
Pseudokellya cardifomis ( -0.66-1.37°C);
Cyclomrdia aatartoides (- 1.90-2.08°C);
Cuspidaria tenella ( -0.42-0*76"C);
Cuspidaria infelix (-0.66-2.08"C).
The ranges for a number of forms which do not reach the Antarctic
Continent may be considered for comparison. Limopsis scotiana Dell,
apparently confined to South Georgia, the South Orkneys and the
South Shetlands, has a very restricted range from -0.48 to 1~32°C.
There thus seems no reason why it could not invade Antarctic waters
from temperature considerations alone. Limopsis Airtella Rochebrune
and Mabille, found in southern South America and the Falklands, has a
range largely confined to water from 4.32 to 8.18"C while Astarte longirostri8, from the Subantarctic and South Georgia, ranges from about
4.91 to 8.30"C.
8. The Scotia Arc as a migration route
The only shallow water migration route between any other shallowwater area and the Antarctic continental shelf is through the scattered
island groups and associated shelves of the Scotia Arc. The arc is bent
right back on itself, the island groups comprising it are relatively
widely spaced, and the major hydrological phenomenon of the Southern
Ocean, the Antarctic Convergence, cuts across it. This is not to be
considered a broad highway through which whole faunas can automatically migrate. It presents a series of gaps which by combinations
of barriers of various kinds filter out families, genera and speaies selectively preventing some from reaching Antarctica, and in turn preventing some Antarctic forms from reaching South America.
Consideration of the extent to which some molluscan families
penetrate the Scotia Arc shows this selective action. A large number
A.X.B.-lO
b