THE BIOLOQY OF ASCIDIANS
59
and the papers by Michaelsen (1918, 1919a, 1920a) remain the chief
source of information, but it may well be true of ascidians, as of other
groups, that the western part of the Indo-West-Pacific region is significantly poorer in species than Indo-Malaya.
Red Sea
About 53 species of ascidian are known from the Red Sea and the
results of Michaelsen (1919b, 1920b) and Kott (1957b) demonstrate
only a small endemic element. The occurrence of the majority of species
also in other parts of the Indo-West-Pacific, as far eastwards as Indonesia and northern Australia, emphasizes the essential unity of the
ascidian fauna of this large region. The modest number of species in the
Red Sea may be partly a result of rather uniform and extreme environmental conditions.
North-west, north and north-east Australia
The northern coastal waters of Australia, from about 29'5 in the
west to about 33"s in the east, support a warm-water and tropical
fauna. The Torres Strait divides this coast into an eastern (Solanderian)
and a western (Dampierian) province, each with perhaps about 50
species. Despite the evidence from echinoderms that these provinces
have distinct faun= (Clark, 1946), there is some doubt whether
ascidian distribution supports the clear separation. Analysis of Kott's
(1957a, 1962, 1963) results shows that 20% of the species examined
occur in both provinces, but this low figure may be due to the scarcity
of records, since more complete collections from the northern coast
(Kott, 1966) indicate that 76% of the species occur in both provinces.
Kott (1966) found a strong relationship between the ascidian faunas of
northern Australia and those of Indonesia, the Philippines and Japan.
Only the Didemnidae provided species with a range extending across
the Indian Ocean to the east African coast ; it may be significant that
this is, systematically, the most difficult of all ascidian families and
therefore the one in which there may be the greatest temptation to
place specimens in species known to occur in other parts of the region.
The fauna of the southern coasts from about Perth to Sydney is
distinct and shows some a0inity with that of New Zealand and even
with cooler more southerly areas according to Kott (1963), who also
found evidence of subdivision of the south coast ascidian fauna.
Tropical and subtropical West Africa
The strictly tropical fauna of West Africa appears to extend from
about 15"N to 15'5, and a related subtropical Mauretanean fauna from
59
and the papers by Michaelsen (1918, 1919a, 1920a) remain the chief
source of information, but it may well be true of ascidians, as of other
groups, that the western part of the Indo-West-Pacific region is significantly poorer in species than Indo-Malaya.
Red Sea
About 53 species of ascidian are known from the Red Sea and the
results of Michaelsen (1919b, 1920b) and Kott (1957b) demonstrate
only a small endemic element. The occurrence of the majority of species
also in other parts of the Indo-West-Pacific, as far eastwards as Indonesia and northern Australia, emphasizes the essential unity of the
ascidian fauna of this large region. The modest number of species in the
Red Sea may be partly a result of rather uniform and extreme environmental conditions.
North-west, north and north-east Australia
The northern coastal waters of Australia, from about 29'5 in the
west to about 33"s in the east, support a warm-water and tropical
fauna. The Torres Strait divides this coast into an eastern (Solanderian)
and a western (Dampierian) province, each with perhaps about 50
species. Despite the evidence from echinoderms that these provinces
have distinct faun= (Clark, 1946), there is some doubt whether
ascidian distribution supports the clear separation. Analysis of Kott's
(1957a, 1962, 1963) results shows that 20% of the species examined
occur in both provinces, but this low figure may be due to the scarcity
of records, since more complete collections from the northern coast
(Kott, 1966) indicate that 76% of the species occur in both provinces.
Kott (1966) found a strong relationship between the ascidian faunas of
northern Australia and those of Indonesia, the Philippines and Japan.
Only the Didemnidae provided species with a range extending across
the Indian Ocean to the east African coast ; it may be significant that
this is, systematically, the most difficult of all ascidian families and
therefore the one in which there may be the greatest temptation to
place specimens in species known to occur in other parts of the region.
The fauna of the southern coasts from about Perth to Sydney is
distinct and shows some a0inity with that of New Zealand and even
with cooler more southerly areas according to Kott (1963), who also
found evidence of subdivision of the south coast ascidian fauna.
Tropical and subtropical West Africa
The strictly tropical fauna of West Africa appears to extend from
about 15"N to 15'5, and a related subtropical Mauretanean fauna from