2. STEROLS: STRUCTURE AND DISTRIBUTION
147
Representatives of its most typical families have been the subject of
some preliminary studies. These have shown convincingly that the
crinoid sterols are also of the levorotatory, A
5 -type (II). Beyond this,
however, very little is known except for an indication that crinoids may
contain one or more sterols not previously encountered in nature (89).
Although the holothurians, or sea cucumbers, are the fleshiest and
least inorganic of the echinoderms, they also contain the relatively lowest amount of fat. Its average unsaponifiable fraction is also below the
usual value for echinoderm fats. Since in addition the sterol content
rarely exceeds 10% of the unsaponifiable fraction, relatively large quantities of holothurians are needed for meaningful studies. This is one of
the major reasons why the sea cucumbers have not yet been as adequately covered as other classes of echinoderms. Only two of the five
orders are represented in Table IX. It is hoped that data on species
from the order of the interesting deep-sea holothurians, Elasipoda, and
from Molpadonia and Apoda will become available in the near future.
All species which have so far been investigated have afforded A
7 -sterols
reminiscent of the starfish sterols, in their low rotations and their color
reactions. Their separation into identifiable compounds has not yet
been accomplished.
Although the echinoids, or sea urchins, include species such as
Arbacia and Echinus, which have been studied intensely by generations
of biologists, our knowledge of their sterols is surprisingly fragmentary.
It may be safely stated, however, that the echinoid sterols are of the
Ä
5 -type (II), and that cholesterol is often if not always a major component. In Arbacia the sterol mixture contains at least 70% of cholesterol
(89). In other sterol mixtures the presence of significant quantities of
additional sterols is indicated by the relatively high melting point of
the crude steryl acetate mixture. Identification of these sterols and the
correlation of their occurrence with the classification and phylogeny of
the echinoids remains an interesting problem.
The species of echinoids listed in Table IX have been arranged on
the basis of the classification given in Hyman's monograph (182). They
do not include representatives from the more primitive order of Cidaroidea, the slate-pencil urchins, nor from the interesting and almost
extinct order of Cassiduloida.
Over forty years ago Mathews (183) called attention to "an important chemical difference between the eggs of the sea urchin and
those of the starfish." From color tests he deduced that sea urchin eggs
contain cholesterol and that starfish eggs do not. Today we know that
this difference does indeed exist, that it is typical also for the entire
animals, and that it even divides the entire phylum. If we were to
147
Representatives of its most typical families have been the subject of
some preliminary studies. These have shown convincingly that the
crinoid sterols are also of the levorotatory, A
5 -type (II). Beyond this,
however, very little is known except for an indication that crinoids may
contain one or more sterols not previously encountered in nature (89).
Although the holothurians, or sea cucumbers, are the fleshiest and
least inorganic of the echinoderms, they also contain the relatively lowest amount of fat. Its average unsaponifiable fraction is also below the
usual value for echinoderm fats. Since in addition the sterol content
rarely exceeds 10% of the unsaponifiable fraction, relatively large quantities of holothurians are needed for meaningful studies. This is one of
the major reasons why the sea cucumbers have not yet been as adequately covered as other classes of echinoderms. Only two of the five
orders are represented in Table IX. It is hoped that data on species
from the order of the interesting deep-sea holothurians, Elasipoda, and
from Molpadonia and Apoda will become available in the near future.
All species which have so far been investigated have afforded A
7 -sterols
reminiscent of the starfish sterols, in their low rotations and their color
reactions. Their separation into identifiable compounds has not yet
been accomplished.
Although the echinoids, or sea urchins, include species such as
Arbacia and Echinus, which have been studied intensely by generations
of biologists, our knowledge of their sterols is surprisingly fragmentary.
It may be safely stated, however, that the echinoid sterols are of the
Ä
5 -type (II), and that cholesterol is often if not always a major component. In Arbacia the sterol mixture contains at least 70% of cholesterol
(89). In other sterol mixtures the presence of significant quantities of
additional sterols is indicated by the relatively high melting point of
the crude steryl acetate mixture. Identification of these sterols and the
correlation of their occurrence with the classification and phylogeny of
the echinoids remains an interesting problem.
The species of echinoids listed in Table IX have been arranged on
the basis of the classification given in Hyman's monograph (182). They
do not include representatives from the more primitive order of Cidaroidea, the slate-pencil urchins, nor from the interesting and almost
extinct order of Cassiduloida.
Over forty years ago Mathews (183) called attention to "an important chemical difference between the eggs of the sea urchin and
those of the starfish." From color tests he deduced that sea urchin eggs
contain cholesterol and that starfish eggs do not. Today we know that
this difference does indeed exist, that it is typical also for the entire
animals, and that it even divides the entire phylum. If we were to