from the zooxanthellae to be “ surprisingly low, especially if the possibility that the zooxanthellae supply the coral host with food materials
is considered.” Indeed, the level of radio-activity wits much lower than
that found by MusccLtinc ilnd 1 L i d , indicnt~ing t h i l t cont1ition.s in
Actiniaria iiiity not bc a soiintl critcrion for thosc in thc Sclcmctinia.
Goreau and Ooreau conclude that at best thc amount of transferred
material could be of little significance as food. However, apart from
their effect on calcium metabolism considered below, they reiterate an
earlier conclusion (Goreau, 1959a), “ that the zooxanthellae may have a
general stimulating action on the coral host’s metabolism, possibly
mediated through vitamin or hormone-like trace factors which are
secreted in small amounts by the algae but which by themselves do not
contribute significantly t o the nutrition of the coral ”. Muscatine (1961)
has shown that green Chlorohydra viridissima withstand starvation or
reduced feeding better than do albino individuals. He considers that
the zoochlorellae may represent a source of coenzymes or coenzyme
precursors to the animal and that this may also be true of the zooxanthellae in hermatypic corals.
The obviously very different conditions existing in many of the
tropical Alcyonacea, especially the Xeniidae, demand mention here.
Species of the Xeniidae are common on Indo-Pacific reefs, being easily
distinguishable owing to the soft velvety appearance of the large
polyps. These show characteristic rhythmical pulsationR recently
studied by Horridge (1‘3.56). The presence of zooxanthellae and the
reduction in the ventral (digestive) mesentcrial filaments have long
been known. Although they possess the typical eight pinnate tentacles,
armed with nematocysts, Gohar (194O), working in the Rcd Sea, found
no reaction to food of any kind. Later (1048) he found similar conditionR
in Cluvularia hamra where also zooxanthellae are abundant and the
mesenterial filaments poorly developed with no gland cells. “ The
endodermic lining of the coelenteric cavities ”, he states, “ is composed
of small cells distended with zooxanthellae, and cofitain nothing else
that may be considered as food.”
I n a series of experiments Gohar (1940) kept colonies of various
species of the Xeniidae in circulating filtered and unfiltered sea water,
similar sets in the light and in the dark. The unfiltered water contained
zooplankton. , 411 colonies kept in the dark gradually ceased t o pulsate,
showed symptoms of starvation and at the end of 2 weeks were beginning to disintegrate and were dying. When returned to the light,
colonies already showing signs of starvation rapidly regained health
and began to pulsate normally. Meanwhile, both Hets of colonies, fed
and starved, kept in the light, remained equally healthy.
is considered.” Indeed, the level of radio-activity wits much lower than
that found by MusccLtinc ilnd 1 L i d , indicnt~ing t h i l t cont1ition.s in
Actiniaria iiiity not bc a soiintl critcrion for thosc in thc Sclcmctinia.
Goreau and Ooreau conclude that at best thc amount of transferred
material could be of little significance as food. However, apart from
their effect on calcium metabolism considered below, they reiterate an
earlier conclusion (Goreau, 1959a), “ that the zooxanthellae may have a
general stimulating action on the coral host’s metabolism, possibly
mediated through vitamin or hormone-like trace factors which are
secreted in small amounts by the algae but which by themselves do not
contribute significantly t o the nutrition of the coral ”. Muscatine (1961)
has shown that green Chlorohydra viridissima withstand starvation or
reduced feeding better than do albino individuals. He considers that
the zoochlorellae may represent a source of coenzymes or coenzyme
precursors to the animal and that this may also be true of the zooxanthellae in hermatypic corals.
The obviously very different conditions existing in many of the
tropical Alcyonacea, especially the Xeniidae, demand mention here.
Species of the Xeniidae are common on Indo-Pacific reefs, being easily
distinguishable owing to the soft velvety appearance of the large
polyps. These show characteristic rhythmical pulsationR recently
studied by Horridge (1‘3.56). The presence of zooxanthellae and the
reduction in the ventral (digestive) mesentcrial filaments have long
been known. Although they possess the typical eight pinnate tentacles,
armed with nematocysts, Gohar (194O), working in the Rcd Sea, found
no reaction to food of any kind. Later (1048) he found similar conditionR
in Cluvularia hamra where also zooxanthellae are abundant and the
mesenterial filaments poorly developed with no gland cells. “ The
endodermic lining of the coelenteric cavities ”, he states, “ is composed
of small cells distended with zooxanthellae, and cofitain nothing else
that may be considered as food.”
I n a series of experiments Gohar (1940) kept colonies of various
species of the Xeniidae in circulating filtered and unfiltered sea water,
similar sets in the light and in the dark. The unfiltered water contained
zooplankton. , 411 colonies kept in the dark gradually ceased t o pulsate,
showed symptoms of starvation and at the end of 2 weeks were beginning to disintegrate and were dying. When returned to the light,
colonies already showing signs of starvation rapidly regained health
and began to pulsate normally. Meanwhile, both Hets of colonies, fed
and starved, kept in the light, remained equally healthy.