ANTARCTIO BENTHOS
149
lacunifera (actiniarians) together with Clavularia franklinianu Roule
(stoloniferan) and Tubularia hdgsoni Hickson and Gravely and Lampra
parwula Hickson and Gravely (hydrozoans). In most areas the large
ascidian Cnemidiocarpa verrucosa is present.
The alcyonarian and the hydroids and sponges feed on suspended
particles but the actinarians Isotealia and Urticinopsis are active predators. Both will feed on large medusae which come within range, but
Urticinopsis preys predominantly on the urchin Xterechinus which
makes up about 77% of the diet of this sea anemone. Dayton, Robilliard
and Paine (1970) illustrate the predation of Sterechinus by Urticinopsis
in a series of beautifully clear underwater photographs. As in Zone I
the most obvious motile animals are Odontaster, Sterechinus, Lineus
and the fishes Trematmus bemutcchii and T . centronotus. In addition
three pycnogonids Thaumastopygnon striata (Mbbius), Colossendeis
robusta Hoek and C. melalonyx Hoek are also common. A whole series
of predator-prey relationships from this zone were noted in this paper.
Zone I I I . Although this zone begins sharply at 33 m, its lower limits
have not been observed or measured. The 33 m level seems to be the
definite lower limit of anchor ice formation. Here the bottom is covered
by a thick mat of sponge spicules and dead bivalve shells, almost always
over 1 m thick. The surface supports an almost complete cover of
living sponges. The sponges support actiniarians, hydroids, polychaetes,
bryozoans and many molluscs, including large numbers of the bivalve
Limatula hodgsoni. The sponge spicule matrix contains a very rich
fauna indeed. Dearborn (1968) has recorded thousands of small gastropods of the genera Margarella and Subonoba per square metre.
The most conspicuous motile animals in this zone are the asteroids
Acodontaster hodgsoni (Bell), A. conspicua (Koehler), Perknuster fuscus
antarcticus and Odontaster meridionalis (all feeding on sponges), Odontaster validus still largely a detritus feeder, Diplasterias brucei attacking
bivalves especially Limatula, and occasional specimens of Macroptychaster accrescens (Koehler) feeding on other echinoderms. A large
nudibranch, Austrodoris mcmurdoensis Odhner was often observed eating sponges. The main predatory univalve seemed to be Trophon
Zongstafi, which drilled through the shells of bivalves, especially
Limatula.
It is obvious that this Zone I11 is one in which most inshore collecting has been done by visiting expeditions in the past. It is certainly the
" McMurdo Sound Glass Sponge Assemblage " of Bullivant (1967, p. 62)
but deserves somewhat more importance than the minor assemblage
status Bullivant gives it.
149
lacunifera (actiniarians) together with Clavularia franklinianu Roule
(stoloniferan) and Tubularia hdgsoni Hickson and Gravely and Lampra
parwula Hickson and Gravely (hydrozoans). In most areas the large
ascidian Cnemidiocarpa verrucosa is present.
The alcyonarian and the hydroids and sponges feed on suspended
particles but the actinarians Isotealia and Urticinopsis are active predators. Both will feed on large medusae which come within range, but
Urticinopsis preys predominantly on the urchin Xterechinus which
makes up about 77% of the diet of this sea anemone. Dayton, Robilliard
and Paine (1970) illustrate the predation of Sterechinus by Urticinopsis
in a series of beautifully clear underwater photographs. As in Zone I
the most obvious motile animals are Odontaster, Sterechinus, Lineus
and the fishes Trematmus bemutcchii and T . centronotus. In addition
three pycnogonids Thaumastopygnon striata (Mbbius), Colossendeis
robusta Hoek and C. melalonyx Hoek are also common. A whole series
of predator-prey relationships from this zone were noted in this paper.
Zone I I I . Although this zone begins sharply at 33 m, its lower limits
have not been observed or measured. The 33 m level seems to be the
definite lower limit of anchor ice formation. Here the bottom is covered
by a thick mat of sponge spicules and dead bivalve shells, almost always
over 1 m thick. The surface supports an almost complete cover of
living sponges. The sponges support actiniarians, hydroids, polychaetes,
bryozoans and many molluscs, including large numbers of the bivalve
Limatula hodgsoni. The sponge spicule matrix contains a very rich
fauna indeed. Dearborn (1968) has recorded thousands of small gastropods of the genera Margarella and Subonoba per square metre.
The most conspicuous motile animals in this zone are the asteroids
Acodontaster hodgsoni (Bell), A. conspicua (Koehler), Perknuster fuscus
antarcticus and Odontaster meridionalis (all feeding on sponges), Odontaster validus still largely a detritus feeder, Diplasterias brucei attacking
bivalves especially Limatula, and occasional specimens of Macroptychaster accrescens (Koehler) feeding on other echinoderms. A large
nudibranch, Austrodoris mcmurdoensis Odhner was often observed eating sponges. The main predatory univalve seemed to be Trophon
Zongstafi, which drilled through the shells of bivalves, especially
Limatula.
It is obvious that this Zone I11 is one in which most inshore collecting has been done by visiting expeditions in the past. It is certainly the
" McMurdo Sound Glass Sponge Assemblage " of Bullivant (1967, p. 62)
but deserves somewhat more importance than the minor assemblage
status Bullivant gives it.