68
R. H. MILLAR
1. northern cold water species (north of Hokkaido and Korea);
2. cosmopolitan species ;
3. north-temperate species (all four main islands) ;
4. warm-water species (southern part of Honsyu Island).
Some 74% of the total occur in southern Japanese waters, although
only about 18% are strictly warm-water species belonging to the warm
Indo-West-Pacific faunistic region and not extending north of the
middle of Honsyu Island. These results confirm and amplify the earlier
work of Oka (1935), who distinguished between the northern and
southern elements in the endemic ascidians of Japan. The faunistic
boundary passing through Honsyu Island corresponds closely to an
abrupt change in the temperature regime brought about by the opposition of cold south-flowing and warm north-flowing currents, and
emphasises the importance of temperature in determining distribution.
The occurrence of 16 species in both southern Japanese and West
Indian waters (Tokioka, 1963) is a remarkable example of the wide
distribution of tropical ascidians.
Indo-Malaya
The sub-region extending from the Indian sub-continent to the
southern coasts of China, and including the Malay archipelago, is known
to be one of the richest in species of any part of the seas. Unfortunately
the collecting effort has been very uneven, relatively little being known
of the ascidians of Indian waters, whereas those of the Malay archipelago
and neighbouring waters have been well studied, principally by Herdman (1881, 1882, 1886), Sluiter (1885, 1904, 1905, 1909), Van Name
(1918) and Tokioka (1950, 1955, 1967). As always, it is difficult to
arrive at the total of good species in the area, but I estimate that there
are about 178 already described. Allowing that less intensive collecting
has been done there than in southern Japanese waters, the islands of
Indonesia must be regarded as comparable in richness. Nevertheless
there may be marked local differences in numbers of species and individuals as Van Name (1918) found in the Philippine Islands. Only
statistical analysis of the results of planned collecting would show
whether such differences result from inadequate sampling or are real
and relate to local variations in habitat.
Western Indian Ocean
Many fewer species are recorded for the western part of the IndoWest-Pacific, which includes the eastern African coast and the islands
of the western Indian Ocean. The area has been but poorly investigated,
R. H. MILLAR
1. northern cold water species (north of Hokkaido and Korea);
2. cosmopolitan species ;
3. north-temperate species (all four main islands) ;
4. warm-water species (southern part of Honsyu Island).
Some 74% of the total occur in southern Japanese waters, although
only about 18% are strictly warm-water species belonging to the warm
Indo-West-Pacific faunistic region and not extending north of the
middle of Honsyu Island. These results confirm and amplify the earlier
work of Oka (1935), who distinguished between the northern and
southern elements in the endemic ascidians of Japan. The faunistic
boundary passing through Honsyu Island corresponds closely to an
abrupt change in the temperature regime brought about by the opposition of cold south-flowing and warm north-flowing currents, and
emphasises the importance of temperature in determining distribution.
The occurrence of 16 species in both southern Japanese and West
Indian waters (Tokioka, 1963) is a remarkable example of the wide
distribution of tropical ascidians.
Indo-Malaya
The sub-region extending from the Indian sub-continent to the
southern coasts of China, and including the Malay archipelago, is known
to be one of the richest in species of any part of the seas. Unfortunately
the collecting effort has been very uneven, relatively little being known
of the ascidians of Indian waters, whereas those of the Malay archipelago
and neighbouring waters have been well studied, principally by Herdman (1881, 1882, 1886), Sluiter (1885, 1904, 1905, 1909), Van Name
(1918) and Tokioka (1950, 1955, 1967). As always, it is difficult to
arrive at the total of good species in the area, but I estimate that there
are about 178 already described. Allowing that less intensive collecting
has been done there than in southern Japanese waters, the islands of
Indonesia must be regarded as comparable in richness. Nevertheless
there may be marked local differences in numbers of species and individuals as Van Name (1918) found in the Philippine Islands. Only
statistical analysis of the results of planned collecting would show
whether such differences result from inadequate sampling or are real
and relate to local variations in habitat.
Western Indian Ocean
Many fewer species are recorded for the western part of the IndoWest-Pacific, which includes the eastern African coast and the islands
of the western Indian Ocean. The area has been but poorly investigated,