THE BIOLOGY OE ASCIDIANS
67
Antiboreal (Subanlarctic) islands
A number of islands in the Southern Ocean are of particular interest
since they are subject to approximately the same water temperatures
but are separated by great distances and sometimes by very deep water.
Kott ( 1969) recognizes a Kerguelen province encompassing Kerguelen, Heard and Macquarie Islands. Although a number of species are
apparently endemic to Kerguelen Island, others occur also at Macquarie
Island some 90' of longitude to the east. She concludes that, despite its
relative nearness to Campbell and Auckland Islands, Macquarie has
more affinity to Kerguelen than to these islands, and only one ascidian
species, Molgula sluiteri (Michaelsen), extends from the South Island
of New Zealand and Chatham Island to Macquarie Island.
The ascidians of Campbell and Auckland Islands are known mainly
from the studies of Bovien (1921)) Michaelsen (1922, 1924) and Brewin
(1950~~). Of the few species recorded, Didemnum studeri Hartmcyer,
Corella eumyota Traustedt and Polyzoa reticulata (Herdman) are
characteristically Subantarctic, and the islands appear to have been
populated from that region rather than from nearby New Zealand,
despite the contrary conclusion by Kott (1969). If this is true, the ascidians conform to the faunistic pattern of the molluscs (Hedley, 1916)
rather than of the sponges and echinoderms (Ekman, 1953).
The Chatham Islands and the relatively shallow Chatham Rise connecting them to the South Island of New Zealand have an ascidian
fauna described by Sluiter (1900), Michaelsen (1922, 1924) and Brewin
(1956b). Brewin showed it to have a close alliance with the ascidian
fauna of New Zealand, 21 of the 33 Chatham species being known from
there. No distinctly southern element is present, in contrast to the
situation in the Campbell and Auckland Islands. The Chatham Islands
lie farther north and, unlike the Campbell and Auckland Islands are
subject to warm northern water in addition to cool southern water.
The Tristan da Cunha group, like the Chatham Islands, lies near thc
Antiboreal Convergence. Occupying a very isolated position between
South Africa and South America, these islands appear to have an
ascidian fauna, so far as can be judged from the very scanty records,
which has some affinity with that of southern South America but none
with the South African fauna (Millar, 1967).
N e w Zealand
Knox (19GO) recognized the Aupourian, Cookian and Forsterian
provinces, and my estimates of respectively about 81, 35 and 58
ascidian species are based for the most part on a series of papers by
67
Antiboreal (Subanlarctic) islands
A number of islands in the Southern Ocean are of particular interest
since they are subject to approximately the same water temperatures
but are separated by great distances and sometimes by very deep water.
Kott ( 1969) recognizes a Kerguelen province encompassing Kerguelen, Heard and Macquarie Islands. Although a number of species are
apparently endemic to Kerguelen Island, others occur also at Macquarie
Island some 90' of longitude to the east. She concludes that, despite its
relative nearness to Campbell and Auckland Islands, Macquarie has
more affinity to Kerguelen than to these islands, and only one ascidian
species, Molgula sluiteri (Michaelsen), extends from the South Island
of New Zealand and Chatham Island to Macquarie Island.
The ascidians of Campbell and Auckland Islands are known mainly
from the studies of Bovien (1921)) Michaelsen (1922, 1924) and Brewin
(1950~~). Of the few species recorded, Didemnum studeri Hartmcyer,
Corella eumyota Traustedt and Polyzoa reticulata (Herdman) are
characteristically Subantarctic, and the islands appear to have been
populated from that region rather than from nearby New Zealand,
despite the contrary conclusion by Kott (1969). If this is true, the ascidians conform to the faunistic pattern of the molluscs (Hedley, 1916)
rather than of the sponges and echinoderms (Ekman, 1953).
The Chatham Islands and the relatively shallow Chatham Rise connecting them to the South Island of New Zealand have an ascidian
fauna described by Sluiter (1900), Michaelsen (1922, 1924) and Brewin
(1956b). Brewin showed it to have a close alliance with the ascidian
fauna of New Zealand, 21 of the 33 Chatham species being known from
there. No distinctly southern element is present, in contrast to the
situation in the Campbell and Auckland Islands. The Chatham Islands
lie farther north and, unlike the Campbell and Auckland Islands are
subject to warm northern water in addition to cool southern water.
The Tristan da Cunha group, like the Chatham Islands, lies near thc
Antiboreal Convergence. Occupying a very isolated position between
South Africa and South America, these islands appear to have an
ascidian fauna, so far as can be judged from the very scanty records,
which has some affinity with that of southern South America but none
with the South African fauna (Millar, 1967).
N e w Zealand
Knox (19GO) recognized the Aupourian, Cookian and Forsterian
provinces, and my estimates of respectively about 81, 35 and 58
ascidian species are based for the most part on a series of papers by