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R. K. DELL
shelf of the continent, A . lorioli Koehler possibly being circum-Antarctic, but all the other species, A . bisdus Mortensen, A . brevisternulis
(Koehler), A. marsupialis (Koehler), A . rostratus (Koehler) and A.
tumescens (Koehler) are on the present evidence known only from East
Antarctica. Species of the genus are known from 0 to 645 m, but most
live deeper than 100 m.
Tripylus has two species represented off the Antarctic Peninsula,
T. cordatus (Koehler) and T. reductus Koehler. This latter species together with a third, T . excavatus Philippi, also occurs in southern South
America.
Tripplaster is represented by T . philippi (Gray) which is distributed
off both coasts of southern South America and also reaches South
Georgia.
Two other families of spatangid echinoids are known from
Antarctio waters, the Urechinidae and the Pourtalesiidae. Both
are essentially deep-sea forms with wide distribution in the ocean
basins.
The family Urechinidae has three genera in the Antarctio Urechinus,
Pilematechinus and Plexechinus. Urechinus drygalskii Mortensen was
described from 3 423 m near the Antarctic Continent. Pilematechinm
veeica (Agassiz) has a very thin test which collapses when the animal
is removed from water (Mortensen, 1950a). It has been collected from
off Chile and from 6.5'42'5 79'49'E in Antarctic waters. The genus is
characteristic of depths from about 2 000 to 4 000 m, P . vesica being
recorded from 3 060 to 4 030 m (Mortensen, 1950). Plexechinus nordenskjoldia Mortensen is known from off South Georgia and the Antarctic
Continent in d e p t h from 110 to 300 m. This is the shallowest record
for any representative of the family. The other unusual feature is that
it is the only member of the family which is apparently brood protecting
(Mortensen, 1950).
The family Pourtalesiidae comprises another group of deep-sea,
forms, none of which is known to be brood protecting. Three species
are recorded from Antarctic waters, Pourtalesia hispida Agassiz from
1 690 to 3 610 m, P . aurorae Koehler from about 440 to 1 690 m and
P. debilis Koehler from 455 m at 64'44'S 97'28'E.
Pifteen genera of echinoids are recorded from south of the Antarctic
Convergence, four restricted to the area, with another six endemic to
the Antarctic-Subantarctic region. Thus 25% of the echinoid genera
are endemic, though 66% of the genera are endemic to the AntarcticSubantarctic. Some 44 species are known from the Antarctic shelf, of
which 77% are endemic (34 species). Of these species the major part
(28 species) are classified in five genera.
R. K. DELL
shelf of the continent, A . lorioli Koehler possibly being circum-Antarctic, but all the other species, A . bisdus Mortensen, A . brevisternulis
(Koehler), A. marsupialis (Koehler), A . rostratus (Koehler) and A.
tumescens (Koehler) are on the present evidence known only from East
Antarctica. Species of the genus are known from 0 to 645 m, but most
live deeper than 100 m.
Tripylus has two species represented off the Antarctic Peninsula,
T. cordatus (Koehler) and T. reductus Koehler. This latter species together with a third, T . excavatus Philippi, also occurs in southern South
America.
Tripplaster is represented by T . philippi (Gray) which is distributed
off both coasts of southern South America and also reaches South
Georgia.
Two other families of spatangid echinoids are known from
Antarctio waters, the Urechinidae and the Pourtalesiidae. Both
are essentially deep-sea forms with wide distribution in the ocean
basins.
The family Urechinidae has three genera in the Antarctio Urechinus,
Pilematechinus and Plexechinus. Urechinus drygalskii Mortensen was
described from 3 423 m near the Antarctic Continent. Pilematechinm
veeica (Agassiz) has a very thin test which collapses when the animal
is removed from water (Mortensen, 1950a). It has been collected from
off Chile and from 6.5'42'5 79'49'E in Antarctic waters. The genus is
characteristic of depths from about 2 000 to 4 000 m, P . vesica being
recorded from 3 060 to 4 030 m (Mortensen, 1950). Plexechinus nordenskjoldia Mortensen is known from off South Georgia and the Antarctic
Continent in d e p t h from 110 to 300 m. This is the shallowest record
for any representative of the family. The other unusual feature is that
it is the only member of the family which is apparently brood protecting
(Mortensen, 1950).
The family Pourtalesiidae comprises another group of deep-sea,
forms, none of which is known to be brood protecting. Three species
are recorded from Antarctic waters, Pourtalesia hispida Agassiz from
1 690 to 3 610 m, P . aurorae Koehler from about 440 to 1 690 m and
P. debilis Koehler from 455 m at 64'44'S 97'28'E.
Pifteen genera of echinoids are recorded from south of the Antarctic
Convergence, four restricted to the area, with another six endemic to
the Antarctic-Subantarctic region. Thus 25% of the echinoid genera
are endemic, though 66% of the genera are endemic to the AntarcticSubantarctic. Some 44 species are known from the Antarctic shelf, of
which 77% are endemic (34 species). Of these species the major part
(28 species) are classified in five genera.