148
WERNER BERGMANN
classify the various species of echinoderms on the basis of their sterol
content, they would fall within two major groups. The one containing
the unusual A
7 -sterols (III) would include the asteroids and holothurians. The other, bearing the A
5 -sterols (II) would embrace the ophiuroids, the echinoids, and the crinoids (8). These differences are so
characteristic as to merit special consideration.
It does not appear probable that such structural differences are
connected with the feeding habits of the animals, and that the sterols
are essentially exogenous and reflect the structures of the food sterols.
The asteroids, which contain A
7 -sterols, feed on all kinds of sessile or
slow-moving animals and also cadavers, all of which contain mainly
A
5 -sterols. In contrast the other A
7 -sterol-containing echinoderms, the
holothurians, are either plankton feeders like the dendrochirotes or extractors of organic matter from surrounding substrates like the aspidochirotes and species belonging to other orders. Similar feeding habits
are also encountered among the A
5 -sterol-containing echinoderms. The
ophiuroids combine ingestion of bottom material with carnivorous feeding. The echinoids are on the whole omnivorous with some, like Echinus,
leaning toward a carnivorous diet, and others like
Strongyhcentrotus,
apparently preferring plant matter, and with certain deep-sea species
acting as general scavengers. Planktonic plants and animals are the
principal food of the crinoids. If exogenous sterols should play a role
in the steroid metabolism of the echinoderms one would have to assume
that where necessary the location of the cyclic double bond will be so
modified as to appear as Δ
7 in some and as Δ
5 in others. The side
chains of these sterols, about which there is so little known at present,
might possibly reflect the structure of the exogenous sterols in the degree
of their unsaturation and their substitution at C-24.
It also does not appear likely, although not impossible, that the
structural differences among the sterols are somehow connected with
the mineral metabolism of the echinoderms. The A
5 -sterol-containing
species all appear substantially more calcareous than those containing
the A
7 -sterols. To judge from the very few reliable values now available
the organic content of the echinoids (12-20%, average 16%) and crinoids
(8-19%, average 15%) are about the same. It is significantly lower than
that of asteroids, which ranges from 12% for Astropecten articulatus to 64%
for the very fleshy Henricea sanguinolenta, or that of the holothurians
which is in excess of 70%. The A
5 -sterol-containing ophiuroids, however,
are not as calcareous as they appear superficially. Their content of
organic matter (19-37%, average 30%) overlaps that of the A
7 -sterolcontaining asteroids.
The author has for some time regarded it more likely that the differ-
WERNER BERGMANN
classify the various species of echinoderms on the basis of their sterol
content, they would fall within two major groups. The one containing
the unusual A
7 -sterols (III) would include the asteroids and holothurians. The other, bearing the A
5 -sterols (II) would embrace the ophiuroids, the echinoids, and the crinoids (8). These differences are so
characteristic as to merit special consideration.
It does not appear probable that such structural differences are
connected with the feeding habits of the animals, and that the sterols
are essentially exogenous and reflect the structures of the food sterols.
The asteroids, which contain A
7 -sterols, feed on all kinds of sessile or
slow-moving animals and also cadavers, all of which contain mainly
A
5 -sterols. In contrast the other A
7 -sterol-containing echinoderms, the
holothurians, are either plankton feeders like the dendrochirotes or extractors of organic matter from surrounding substrates like the aspidochirotes and species belonging to other orders. Similar feeding habits
are also encountered among the A
5 -sterol-containing echinoderms. The
ophiuroids combine ingestion of bottom material with carnivorous feeding. The echinoids are on the whole omnivorous with some, like Echinus,
leaning toward a carnivorous diet, and others like
Strongyhcentrotus,
apparently preferring plant matter, and with certain deep-sea species
acting as general scavengers. Planktonic plants and animals are the
principal food of the crinoids. If exogenous sterols should play a role
in the steroid metabolism of the echinoderms one would have to assume
that where necessary the location of the cyclic double bond will be so
modified as to appear as Δ
7 in some and as Δ
5 in others. The side
chains of these sterols, about which there is so little known at present,
might possibly reflect the structure of the exogenous sterols in the degree
of their unsaturation and their substitution at C-24.
It also does not appear likely, although not impossible, that the
structural differences among the sterols are somehow connected with
the mineral metabolism of the echinoderms. The A
5 -sterol-containing
species all appear substantially more calcareous than those containing
the A
7 -sterols. To judge from the very few reliable values now available
the organic content of the echinoids (12-20%, average 16%) and crinoids
(8-19%, average 15%) are about the same. It is significantly lower than
that of asteroids, which ranges from 12% for Astropecten articulatus to 64%
for the very fleshy Henricea sanguinolenta, or that of the holothurians
which is in excess of 70%. The A
5 -sterol-containing ophiuroids, however,
are not as calcareous as they appear superficially. Their content of
organic matter (19-37%, average 30%) overlaps that of the A
7 -sterolcontaining asteroids.
The author has for some time regarded it more likely that the differ-