THE BIOLOGY OF ASCIDIANS
63
somewhere near Cape Cod. The ascidian fauna of the region is an impoverished one and includes only about 46 species. A number of these
are common to both sides of the Atlantic, and Huus (1927) noted that
24 of the 28 European boreo-arctic species but only 4 out of 46 European boreal and south boreal species occur also on the American coast.
Temperate north-euatern Pacijic
The Pacific coast of North America, from lower California to the
Alaskan peninsula, forms one faunistic unit, with more or less distinct
subdivisions, and Van Name (1945) distinguishes an element centred
on the coast of northern California and another on the coast of British
Columbia. Water along most of the coast is rather uniform in temperature.
The ascidian fauna is not rich, with only about 43 species (Tokioka,
1963), several of which occur over a large north-to-south range.
Tokioka contrasts this with the richer fauna of the north temperate
waters of the western Pacific, and notes in particular the scarcity of
species of Pyura and the absence of Polymrpa, Microcosmus and the
subfamily Diazoninae on the American side.
Temperate north-western Pacijic
The coastal area from about the middle of Honsyu Island, Japan
northwards to the eastern coast of the Kamchatka Peninsula constitutes one faunistic region, occupied by temperate and cool-water
species. Within this area some 73 cool-water species, and 152 north
temperate-water species of ascidian are recorded (Tokioka, 1963),
representing a very rich fauna. A number of these occur also on the
Pacific coast of North America.
Arctic
The whole of the Arctic is a fairly homogeneous zoogeographical
unit, with only partial longitudinal division into areas having distinct
faunas. Hartmeyer (1904) noted this with regard to ascidians, and confirmation is found in subsequent work by Hartmeyer (1923, 1924),
h b a c k (1922, 1923, 1928, 1934) and Van Name (1945). The distributional maps in Hartmeyer’s account of the Ingolf Expedition show
how commonly Arctic species, especially those of the high Arctic, have
a circumpolar distribution. There appear to be about 80 species of
Arctic ascidians, and the fauna is not only quite rich in species but
locally very rich in individuals. MacGinitie (1955) and Abbott (1966)
found them to be one of the dominant groups of marine invertebrates
at Cape Thompson, Alaska. In any given area the ascidian fauna itself
63
somewhere near Cape Cod. The ascidian fauna of the region is an impoverished one and includes only about 46 species. A number of these
are common to both sides of the Atlantic, and Huus (1927) noted that
24 of the 28 European boreo-arctic species but only 4 out of 46 European boreal and south boreal species occur also on the American coast.
Temperate north-euatern Pacijic
The Pacific coast of North America, from lower California to the
Alaskan peninsula, forms one faunistic unit, with more or less distinct
subdivisions, and Van Name (1945) distinguishes an element centred
on the coast of northern California and another on the coast of British
Columbia. Water along most of the coast is rather uniform in temperature.
The ascidian fauna is not rich, with only about 43 species (Tokioka,
1963), several of which occur over a large north-to-south range.
Tokioka contrasts this with the richer fauna of the north temperate
waters of the western Pacific, and notes in particular the scarcity of
species of Pyura and the absence of Polymrpa, Microcosmus and the
subfamily Diazoninae on the American side.
Temperate north-western Pacijic
The coastal area from about the middle of Honsyu Island, Japan
northwards to the eastern coast of the Kamchatka Peninsula constitutes one faunistic region, occupied by temperate and cool-water
species. Within this area some 73 cool-water species, and 152 north
temperate-water species of ascidian are recorded (Tokioka, 1963),
representing a very rich fauna. A number of these occur also on the
Pacific coast of North America.
Arctic
The whole of the Arctic is a fairly homogeneous zoogeographical
unit, with only partial longitudinal division into areas having distinct
faunas. Hartmeyer (1904) noted this with regard to ascidians, and confirmation is found in subsequent work by Hartmeyer (1923, 1924),
h b a c k (1922, 1923, 1928, 1934) and Van Name (1945). The distributional maps in Hartmeyer’s account of the Ingolf Expedition show
how commonly Arctic species, especially those of the high Arctic, have
a circumpolar distribution. There appear to be about 80 species of
Arctic ascidians, and the fauna is not only quite rich in species but
locally very rich in individuals. MacGinitie (1955) and Abbott (1966)
found them to be one of the dominant groups of marine invertebrates
at Cape Thompson, Alaska. In any given area the ascidian fauna itself