ANTARCTIO BENTHOS
103
gaussi, and Dentalium (Fissidentalium) majorinum reaching their limits
about the northern shores of Magellan Strait, while Cyamiocardium and
Limopsis marionensis reach to about 40"s on the west coast.
An analysis of the bivalves and scaphopods of East Antarctica which
also occur in parts of West Antarctica and the island groups of the
Scotia Arc, gives supporting evidence for these latter to be considered
a series of stepping stones (Table VI).
9. The origins of the Antarctic Mollusca
Antarctic 1
Three faunal elements are obvious amongst the Mollusca of the
1. forms with deep-water affinities;
2. forms which show evidence of derivation from South America
through the Scotia Arc;
3. genera and species which have no obvious immediate affinity,
and which appear to be an " old " Antarctic element.
1. Genera which appear to be deep-water derivatives include the
nuculids and nuculanids, although the genus Propeleda and the subgenus Aequiyoldia seem to be local Antarctic evolutionary products.
Propeleda is very close to Nuculana (s. str) and is probably derived from
this genus. Malletia, Bathyarca, Limopsis, Dacrydium, Cyclopecten,
Limatula, Thyasira, Lyonsia, Plwladomya, Thracia, Lyonsiella,
Poromya and Cuspidaria are all bivalves well represented in deep water
elsewhere. Burne (1920) noted that Limatula hodgsoni has some less
specialized and apparently more primitive anatomical features amongst
the Limidae, but the anatomy of too few forms is known for too much
weight to be placed on this evidence. But because bivalves are placed
in this category does not mean that they are not at the same time
" old " inhabitants of Antarctica. Amongst the gastropods with fairly
obviously deep-water afinity are the turrids Aforia, Leucosyrinx,
Pleurotomella and Pontiothauma, and the limpets Puncturella and
Lepeta.
2. Apart from forms which have not as yet penetrated any farther
into the Antarctic than various island groups of the Scotia Arc, the
Antarctic Peninsula or the other areas of West Antarctica, there is an
element of the widespread Antarctic fauna which appears to have been
derived through this migration route a t an earlier period. Genera concerned would include Nuttalochiton, Philobrya, Astarte and Cyclocardia.
3. Soot-Ryen (1961) discussed an " old " Antarctic fauna as, " the
remains of an earlier Antarctic fauna with ancestors from a time of more
genial climatic conditions ". Such genera and species as follows seem
103
gaussi, and Dentalium (Fissidentalium) majorinum reaching their limits
about the northern shores of Magellan Strait, while Cyamiocardium and
Limopsis marionensis reach to about 40"s on the west coast.
An analysis of the bivalves and scaphopods of East Antarctica which
also occur in parts of West Antarctica and the island groups of the
Scotia Arc, gives supporting evidence for these latter to be considered
a series of stepping stones (Table VI).
9. The origins of the Antarctic Mollusca
Antarctic 1
Three faunal elements are obvious amongst the Mollusca of the
1. forms with deep-water affinities;
2. forms which show evidence of derivation from South America
through the Scotia Arc;
3. genera and species which have no obvious immediate affinity,
and which appear to be an " old " Antarctic element.
1. Genera which appear to be deep-water derivatives include the
nuculids and nuculanids, although the genus Propeleda and the subgenus Aequiyoldia seem to be local Antarctic evolutionary products.
Propeleda is very close to Nuculana (s. str) and is probably derived from
this genus. Malletia, Bathyarca, Limopsis, Dacrydium, Cyclopecten,
Limatula, Thyasira, Lyonsia, Plwladomya, Thracia, Lyonsiella,
Poromya and Cuspidaria are all bivalves well represented in deep water
elsewhere. Burne (1920) noted that Limatula hodgsoni has some less
specialized and apparently more primitive anatomical features amongst
the Limidae, but the anatomy of too few forms is known for too much
weight to be placed on this evidence. But because bivalves are placed
in this category does not mean that they are not at the same time
" old " inhabitants of Antarctica. Amongst the gastropods with fairly
obviously deep-water afinity are the turrids Aforia, Leucosyrinx,
Pleurotomella and Pontiothauma, and the limpets Puncturella and
Lepeta.
2. Apart from forms which have not as yet penetrated any farther
into the Antarctic than various island groups of the Scotia Arc, the
Antarctic Peninsula or the other areas of West Antarctica, there is an
element of the widespread Antarctic fauna which appears to have been
derived through this migration route a t an earlier period. Genera concerned would include Nuttalochiton, Philobrya, Astarte and Cyclocardia.
3. Soot-Ryen (1961) discussed an " old " Antarctic fauna as, " the
remains of an earlier Antarctic fauna with ancestors from a time of more
genial climatic conditions ". Such genera and species as follows seem