112
R. K. DELL
neither of these factors is the regulating one. Pearse supposes that the
period of phytoplankton production (the onset of which is fairly sudden
and uniform throughout) may be the controlling factor.
Eggs and sperm at spawning time are shed into the sea water where
fertilization occurs. Early development of the fertilized embryo follows
the usual pattern for starfish with indirect development through a
blastula, a gastrula and then to the typical bipinnaria. Development has
not been traced beyond this stage. Up to the bipinnaria development is
remarkably slow but this results in the main feeding stage occurring
when diatom food is available. All the evidence points to the fact that,
unlike most other seastar larvae known, the developing stages of
Odontaster swim close to the bottom. No larval stages have been collected from the plankton. Such a habit with the larval stages keeping
near the bottom represents in Pearse’s opinion a aompromise allowing
efficient dispersal without exposing the larvae to the hazardous conditions in the plankton.
Growth appears to be very slow throughout its life. Pearse shows
that growth may take place a t a rate of only a few grammes a year,
that they do not begin t o spawn until they are between three and six
years old, and that large specimens of about 100 g weight may well be
between 60 and 100 years old and perhaps even older.
Pearse found 0. validus to be remarkably free of predators and
commensals and believes this species to be near a top trophic level in
this environment, with population regulation coming in part through
the effect of available food supply and production of gametes.
A. M. Clark (1962) has given keys to orders, families, genera and
species of Southern Ocean seastars.
3. Ophiuroidea
Knowledge of the Antarctic brittle stars has been derived mainly
from the work of Koehler (in a series of papers 1901-23), Hertz (1926),
Mortensen (1937), Fell (1961) and Madsen (1967). McKnight (1967)
and Sen0 and Irimura (1968) have recently described a new species
each from the Ross Sea, while Arnaud (1964) has given much information on the occurrence of the group in relatively shallow water off
Adelie Land.
Ophiuroids are one of the commonest groups represented in the
Antarctic benthic fauna. I n places in the Ross Sea they may form onethird the total biomass (Fell, 1961). Calculations based upon bottom
photographs between 75 and 350 m, show that in local concentrations
ophiuroids may be aa plentiful as 10000000/km2. Ophiacizntha
R. K. DELL
neither of these factors is the regulating one. Pearse supposes that the
period of phytoplankton production (the onset of which is fairly sudden
and uniform throughout) may be the controlling factor.
Eggs and sperm at spawning time are shed into the sea water where
fertilization occurs. Early development of the fertilized embryo follows
the usual pattern for starfish with indirect development through a
blastula, a gastrula and then to the typical bipinnaria. Development has
not been traced beyond this stage. Up to the bipinnaria development is
remarkably slow but this results in the main feeding stage occurring
when diatom food is available. All the evidence points to the fact that,
unlike most other seastar larvae known, the developing stages of
Odontaster swim close to the bottom. No larval stages have been collected from the plankton. Such a habit with the larval stages keeping
near the bottom represents in Pearse’s opinion a aompromise allowing
efficient dispersal without exposing the larvae to the hazardous conditions in the plankton.
Growth appears to be very slow throughout its life. Pearse shows
that growth may take place a t a rate of only a few grammes a year,
that they do not begin t o spawn until they are between three and six
years old, and that large specimens of about 100 g weight may well be
between 60 and 100 years old and perhaps even older.
Pearse found 0. validus to be remarkably free of predators and
commensals and believes this species to be near a top trophic level in
this environment, with population regulation coming in part through
the effect of available food supply and production of gametes.
A. M. Clark (1962) has given keys to orders, families, genera and
species of Southern Ocean seastars.
3. Ophiuroidea
Knowledge of the Antarctic brittle stars has been derived mainly
from the work of Koehler (in a series of papers 1901-23), Hertz (1926),
Mortensen (1937), Fell (1961) and Madsen (1967). McKnight (1967)
and Sen0 and Irimura (1968) have recently described a new species
each from the Ross Sea, while Arnaud (1964) has given much information on the occurrence of the group in relatively shallow water off
Adelie Land.
Ophiuroids are one of the commonest groups represented in the
Antarctic benthic fauna. I n places in the Ross Sea they may form onethird the total biomass (Fell, 1961). Calculations based upon bottom
photographs between 75 and 350 m, show that in local concentrations
ophiuroids may be aa plentiful as 10000000/km2. Ophiacizntha