104
R. K. DELL
to belong in this group: Adamwsium colbecki, Adacnarca, Laternula,
Ptycbcardia, Cyamiocurdium, Pseudokellya, Dentalium (Pissidentalium) majorinum, Cadulus dalli antarcticus, and possibly Limatula
bdgsoni, Thracia meridionalis, Limopsis marionensis and Cyclocardia
aetartoides. Amongst the gastropods this group probably includes Submargarita, Antimurgarita, Falsimargarita, Cerithiqsilla, Chlanidota,
Neobuccinum and Prosipb as well as the series of trichotropid genera
Antitrichotropis, Trichoconcha, Neoconcha and Discotrichoconcha. This
latter group, obviously representing another example of explosive
adaptation as does the plethora of Antarctic genera of buccinacean
origin, must surely have had an earlier derivation. The genus Laternula,
represented by the widely distributed L. elliptica, in the Antarctic and
Subantarctic, a large thin-shelled bivalve genus, is otherwise found
only in the tropical Indo-Pacific with one species in southern Australia
and Tasmania, but lacking any other representation in South Africa or
New Zealand or in South America (Soot-Ryen, 1951; Powell, 1965).
10. South Ueorgia
The Mollusca of South Georgia mirror the faunal mixture seen in so
many other groups. Some 164 species of benthic Mollusca have been
recorded from South Georgia, of which 98 species are found nowhere
else. This high endemic element may be more apparent than real when
careful comparisons can be made between the total South Georgian
molluscan fauna and that of the other islands of the Scotia Arc. Many
of the shallow-water South Georgian forms described by Martens
and Pfeffer (1886) must be assessed in the light of modern systematic
practice, and with adequate new collections. However, even if the
percentage of apparent endemism is lowered, to some extent, there
will still be a strong unique element. The presence of a number of
endemic genera of gastropods adds to this distinctive character, e.g.
Promargarita, Pfefferia, Chlanidotella and Cauineptunea. At the same
time for Mollusca as for most other groups South Georgia acts as a
staging area on the migration route from South America through the
Scotia Arc to Antarctica, and similarly in the reverse direction.
Q. Echinodermata
1. Echinoidea
Apart from some general papers on echinoderms our main knowledge of the Antarctic echinoids has come from papers by Koehler
1926), Bernasconi (1953) and particularly by Mortensen (1909, 1910,
1928, 1950a, 1961). Pawson (1969b) has given a review and illustrations of distribution patterns.
R. K. DELL
to belong in this group: Adamwsium colbecki, Adacnarca, Laternula,
Ptycbcardia, Cyamiocurdium, Pseudokellya, Dentalium (Pissidentalium) majorinum, Cadulus dalli antarcticus, and possibly Limatula
bdgsoni, Thracia meridionalis, Limopsis marionensis and Cyclocardia
aetartoides. Amongst the gastropods this group probably includes Submargarita, Antimurgarita, Falsimargarita, Cerithiqsilla, Chlanidota,
Neobuccinum and Prosipb as well as the series of trichotropid genera
Antitrichotropis, Trichoconcha, Neoconcha and Discotrichoconcha. This
latter group, obviously representing another example of explosive
adaptation as does the plethora of Antarctic genera of buccinacean
origin, must surely have had an earlier derivation. The genus Laternula,
represented by the widely distributed L. elliptica, in the Antarctic and
Subantarctic, a large thin-shelled bivalve genus, is otherwise found
only in the tropical Indo-Pacific with one species in southern Australia
and Tasmania, but lacking any other representation in South Africa or
New Zealand or in South America (Soot-Ryen, 1951; Powell, 1965).
10. South Ueorgia
The Mollusca of South Georgia mirror the faunal mixture seen in so
many other groups. Some 164 species of benthic Mollusca have been
recorded from South Georgia, of which 98 species are found nowhere
else. This high endemic element may be more apparent than real when
careful comparisons can be made between the total South Georgian
molluscan fauna and that of the other islands of the Scotia Arc. Many
of the shallow-water South Georgian forms described by Martens
and Pfeffer (1886) must be assessed in the light of modern systematic
practice, and with adequate new collections. However, even if the
percentage of apparent endemism is lowered, to some extent, there
will still be a strong unique element. The presence of a number of
endemic genera of gastropods adds to this distinctive character, e.g.
Promargarita, Pfefferia, Chlanidotella and Cauineptunea. At the same
time for Mollusca as for most other groups South Georgia acts as a
staging area on the migration route from South America through the
Scotia Arc to Antarctica, and similarly in the reverse direction.
Q. Echinodermata
1. Echinoidea
Apart from some general papers on echinoderms our main knowledge of the Antarctic echinoids has come from papers by Koehler
1926), Bernasconi (1953) and particularly by Mortensen (1909, 1910,
1928, 1950a, 1961). Pawson (1969b) has given a review and illustrations of distribution patterns.